Adafruit METRO M0 Express User Manual

Download

Adafruit Metro M0 Express

Created by lady ada

https://learn.adafruit.com/adafruit-metro-m0-express

Last updated on 2022-01-01 02:33:36 PM EST

©Adafruit Industries Page 1 of 238

Overview

Pinouts

• Power Connections

• Logic pins

• SPI Flash and NeoPixel

• Other Pins!

• Debug Interface

UF2 Bootloader Details

• Entering Bootloader Mode

• Using the Mass Storage Bootloader

• Using the BOSSA Bootloader

• Running bossac on the command line

• Updating the bootloader

• Getting Rid of Windows Pop-ups

• Making your own UF2

• Installing the bootloader on a fresh/bricked board

Arduino IDE Setup

Using with Arduino IDE

• Install SAMD Support

• Install Adafruit SAMD

• Install Drivers (Windows 7 & 8 Only)

• Blink

• Successful Upload

• Compilation Issues

• Manually bootloading

• Ubuntu& Linux Issue Fix

13 15 17 18 19

24 25 28 30

38 40

41 42 43 43

Adapting Sketches to M0 & M4

• Analog References

• Pin Outputs & Pullups

• Serial vs SerialUSB

• AnalogWrite / PWM on Feather/Metro M0

• analogWrite() PWM range

• analogWrite() DAC on A0

• Missing header files

• Bootloader Launching

• Aligned Memory Access

• Floating Point Conversion

• How Much RAM Available?

• Storing data in FLASH

• Pretty-Printing out registers

• M4 Performance Options

• CPU Speed (overclocking)

• Optimize

• Cache

• Max SPI and Max QSPI

• Enabling the Buck Converter on some M4 Boards

44 44 44 45

47 47 47 48 48 48

49 49 50 50

©Adafruit Industries Page 2 of 238

Using SPI Flash

• Read & Write CircuitPython Files

• Format Flash Memory

• Datalogging Example

• Reading and Printing Files

• Full Usage Example

• Accessing SPI Flash

58 58 59

Metro M0 HELP!

What is CircuitPython?

• CircuitPython is based on Python

• Why would I use CircuitPython?

CircuitPython

• Set up CircuitPython Quick Start!

• Further Information

Installing the Mu Editor

• Download and Install Mu

• Starting Up Mu

• Using Mu

Creating and Editing Code

• Creating Code

• Editing Code

• Back to Editing Code...

• Naming Your Program File

Connecting to the Serial Console

• Are you using Mu?

• Serial Console Issues or Delays on Linux

• Setting Permissions on Linux

• Using Something Else?

68 69 69

71 73 74 75

76 77 77 78

Interacting with the Serial Console

The REPL

• Entering the REPL

• Interacting with the REPL

• Returning to the Serial Console

CircuitPython Libraries

• The Adafruit CircuitPython Library Bundle

• Downloading the Adafruit CircuitPython Library Bundle

• The CircuitPython Community Library Bundle

• Downloading the CircuitPython Community Library Bundle

• Understanding the Bundle

• Example Files

• Copying Libraries to Your Board

• Understanding Which Libraries to Install

• Example: ImportError Due to Missing Library

• Library Install on Non-Express Boards

• Updating CircuitPython Libraries and Examples

©Adafruit Industries Page 3 of 238

87 87

88 88 89 90 90 90

94 95

Frequently Asked Questions

Troubleshooting

• Always Run the Latest Version of CircuitPython and Libraries

• I have to continue using CircuitPython 5.x or earlier. Where can I find compatible libraries?

• Bootloader (boardnameBOOT) Drive Not Present

• Windows Explorer Locks Up When Accessing boardnameBOOT Drive

• Copying UF2 to boardnameBOOT Drive Hangs at 0% Copied

• CIRCUITPY Drive Does Not Appear

• Device Errors or Problems on Windows

• Serial Console in Mu Not Displaying Anything

• code.py Restarts Constantly

• CircuitPython RGB Status Light

• CircuitPython 7.0.0 and Later

• CircuitPython 6.3.0 and earlier

• Serial console showing ValueError: Incompatible .mpy file

• CIRCUITPY Drive Issues

• Safe Mode

• To erase CIRCUITPY: storage.erase_filesystem()

• Erase CIRCUITPY Without Access to the REPL

• For the specific boards listed below:

• For SAMD21 non-Express boards that have a UF2 bootloader:

• For SAMD21 non-Express boards that do not have a UF2 bootloader:

• Running Out of File Space on SAMD21 Non-Express Boards

• Delete something!

• Use tabs

• On MacOS?

• Prevent & Remove MacOS Hidden Files

• Copy Files on MacOS Without Creating Hidden Files

• Other MacOS Space-Saving Tips

• Device Locked Up or Boot Looping

99 99

100

101

101 102 102

103 104 104 104

105

107 107 107

109

110

112

113

114

115

116

Welcome to the Community!

• Adafruit Discord

• CircuitPython.org

• Adafruit GitHub

• Adafruit Forums

• Read the Docs

Advanced Serial Console on Windows

• Windows 7 and 8.1

• What's the COM?

• Install Putty

Advanced Serial Console on Mac

• What's the Port?

• Connect with screen

"Uninstalling" CircuitPython

• Backup Your Code

• Moving Circuit Playground Express to MakeCode

• Moving to Arduino

CircuitPython Essentials

117

118

119

123 125 126

126

126 127 128

130

131

132

133 133 134

135

©Adafruit Industries Page 4 of 238

CircuitPython Pins and Modules

• CircuitPython Pins

• import board

• I2C, SPI, and UART

• What Are All the Available Names?

• Microcontroller Pin Names

• CircuitPython Built-In Modules

136

137

137 138 139 140

141

CircuitPython Built-Ins

• Thing That Are Built In and Work

• Flow Control

• Math

• Tuples, Lists, Arrays, and Dictionaries

• Classes, Objects and Functions

• Lambdas

• Random Numbers

CircuitPython Digital In & Out

• Find the pins!

• Read the Docs

CircuitPython Analog In

• Creating the analog input

• get_voltage Helper

• Main Loop

• Changing It Up

• Wire it up

• Reading Analog Pin Values

CircuitPython Analog Out

• Creating an analog output

• Setting the analog output

• Main Loop

• Find the pin

142

142 142 142 142 142 143 143

143

145 148

148

148 149 149 149

150

153

154

154 154 155 155

CircuitPython PWM

• PWM with Fixed Frequency

• Create a PWM Output

• Main Loop

• PWM Output with Variable Frequency

• Wire it up

• Where's My PWM?

CircuitPython Servo

• Servo Wiring

• Standard Servo Code

• Continuous Servo Code

CircuitPython Cap Touch

• Create the Touch Input

• Main Loop

• Find the Pin(s)

CircuitPython Internal RGB LED

• Create the LED

158

159

160 160 160

162 167

168

168 170

171

172

173

174

177

178

©Adafruit Industries Page 5 of 238

• Brightness

• Main Loop

• Making Rainbows (Because Who Doesn't Love 'Em!)

• Circuit Playground Express Rainbow

178 179 180

181

CircuitPython NeoPixel

• Wiring It Up

• The Code

• Create the LED

• NeoPixel Helpers

• Main Loop

• NeoPixel RGBW

• Read the Docs

CircuitPython DotStar

• Wire It Up

• The Code

• Create the LED

• DotStar Helpers

• Main Loop

• Is it SPI?

• Read the Docs

CircuitPython UART Serial

• The Code

• Wire It Up

• Where's my UART?

• Trinket M0: Create UART before I2C

182

182 183 184 185 185 186 187

187

188 189

191 192 192 193 193

194

195 196 199

200

CircuitPython I2C

• Wire It Up

• Find Your Sensor

• I2C Sensor Data

• Where's my I2C?

CircuitPython HID Keyboard and Mouse

• CircuitPython Keyboard Emulator

• Create the Objects and Variables

• The Main Loop

• Non-US Keyboard Layouts

• CircuitPython Mouse Emulator

• Create the Objects and Variables

• CircuitPython HID Mouse Helpers

• Main Loop

CircuitPython CPU Temp

CircuitPython Storage

• Logging the Temperature

CircuitPython Expectations

• Always Run the Latest Version of CircuitPython and Libraries

• I have to continue using CircuitPython 3.x or 2.x, where can I find compatible libraries?

• Switching Between CircuitPython and Arduino

• The Difference Between Express And Non-Express Boards

201

201 204 205 207

208

210

211

211 213 213 214

214

215

218

220

220 220

221 221

©Adafruit Industries Page 6 of 238

• Non-Express Boards: Gemma, Trinket, and QT Py

• Differences Between CircuitPython and MicroPython

• Differences Between CircuitPython and Python

222 222 222

MakeCode

What is MakeCode Maker?

Custom Extensions

• Account setup

• Commit and push

• Conflicts

• Testing your package

Editing Blocks

• Blinky!

Editing JavaScript

• Blocks to JavaScript

Downloading and Flashing

• Step 1: Connect your board via USB

• Step 2: Test your code in the simulator

• Step 3: Download and flash your code

Saving and Sharing

• Extracting your code from the board

• Sharing

224

227

227 228 230 230

231

232

233

234 234 235

236

236 236

Downloads

• Files

• Schematic & Fabrication Print

237

237 237

©Adafruit Industries Page 7 of 238

©Adafruit Industries Page 8 of 238

Overview

Metro is our series of microcontroller boards for use with the Arduino IDE. This new Metro board looks a whole lot like our original Metro 328(https://adafru.it/

METROXMETR), but with a huge upgrade. Instead of the ATmega328, this Metro

features a ATSAMD21G18 chip, an ARM Cortex M0+. It's our first Metro that is designed for use with CircuitPython! CircuitPython is our beginner-oriented flavor of MicroPython - and as the name hints at, its a small but full-featured version of the popular Python programming language specifically for use with circuitry and electronics.

Not only can you use CircuitPython, but the Metro M0 is also usable in the Arduino IDE. You can also use MakeCode(https://adafru.it/C9N)'s block-based GUI coding environment on this board.

©Adafruit Industries Page 9 of 238

The Metro M0's SAMD21 is a very minimal chip for CircuitPython, at the time it was the first board we designed that could use it but chips have gotten better since then. To really have a good experience we recommend a Metro M4

At the Metro M0's heart is an ATSAMD21G18 ARM Cortex M0 processor, clocked at 48 MHz and at 3.3V logic, the same one used in the newArduino Zero(http://adafru.it/

2843). This chip has a whopping 256K of FLASH (8x more than the Atmega328) and

32K of RAM (16x as much)! This chip comes with built in USB so it has USB-to-Serial program & debug capability built in with no need for an FTDI-like chip.

Power the METRO with 7-9V polarity protected DC or the micro USB connector

• to any 5V USB source. The 2.1mm DC jack has an on/off switch next to it so you can turn off your setup easily. The METRO will automagically switch between USB and DC. METRO has 25 GPIO pins, 12 of which are analog in, and one of which is a true

• analog out. There's a hardware SPI port, hardware I2C port and hardware UART. Logic level is 3.3V Native USB, there's no need for a hardware USB to Serial converter as the Metro

• M0 has built in USB support. When used to act like a serial device, the USB interface can be used by any computer to listen/send data to the METRO, and can also be used to launch and update code via the bootloader. It can also act like a keyboard, mouse or MIDI device as well. Four indicator LEDs and one NeoPixel, on the front edge of the PCB, for easy

• debugging. One green power LED, two RX/TX LEDs for data being sent over

©Adafruit Industries Page 10 of 238

USB, and a red LED connected. Next to the reset button there is an RGB NeoPixel that can be used for any purpose. 2 MB SPI Flash storage chip is included on board. You can use the SPI Flash

• storage like a very tiny hard drive. When used in Circuit Python, the 2 MB flash acts as storage for all your scripts, libraries and files. When used in Arduino, you can read/write files to it, like a little datalogger or SD card, and then with our helper program, access the files over USB. Easy reprogramming, comes pre-loaded with the UF2 bootloader(https://

•

adafru.it/wbC), which looks like a USB key. Simply drag firmware on to program,

no special tools or drivers needed! It can be used by MakeCode or Arduino IDE (in bossa compatibility)

Here's some handy specs!

Measures 2.8" x 2.1" x 0.28"

• ATSAMD21G18 @ 48MHz with 3.3V logic/power

• 256KB of FLASH + 32KB of RAM

• 4 MB SPI Flash chip

• No EEPROM

•

32.768 KHz crystal for clock generation & RTC

•

3.3V regulator with 500mA peak current output

• USB native support, comes with USB bootloader and serial port debugging

• You also get tons of pins - 25 GPIO pins, 5 more than the Metro 328

• Hardware Serial, hardware I2C, hardware SPI support

• PWM outputs on almost all pins

• 6 x 12-bit analog inputs

•

©Adafruit Industries Page 11 of 238

1 x 10-bit analog output (DAC)

• Built in NeoPixel on pin #40

• Pin #13 red LED for general purpose blinking

• Power on/off switch

• 4 mounting holes

• We also include 4 rubber bumpers to keep it from slipping off your desk

• Reset button

•

Please note, CircuitPython is still in beta and we're working hard to make it awesome! Please pick up one of these Metro M0 Expresses if you want to try it out - maybe even help us find bugs and make improvements!

©Adafruit Industries Page 12 of 238

Pinouts

The Metro M0 is chock-full of microcontroller goodness. There's also a lot of pins and ports. We'll take you a tour of them now!

Power Connections

©Adafruit Industries Page 13 of 238

There's a lot of ways to power the Metro M0 Express, and a lot of ways to get power out as well.

There are two primary ways to power the Metro:

Through the Micro USB port up at the top left

• Through the DC jack at the bottom left

•

The MicroUSB jack provides 5V at 500mA or so, there is a fuse that will shut off temporarily when more than 1000mA is drawn, this is to protect a computer USB port. You can plug this into any computer or USB charger with a USB cable. You can draw up to 500mA between the Vin, 5V and 3.3V supplies (combined).

The DC Jack is a 5.5mm/2.1mm center-positive DC connector, which is the most common available. Provide about 6V-12V here to power the Metro. There is no fuse on this connection so you can draw more current, up to 800mA between the 5V and

3.3V supplies, and 2A from Vin.

Onboard regulators take the USB or DC power and linearly convert it to 3.3V and 5V:

3V - this is the output from the 3.3V regulator, it can supply 500mA peak

• 5V - this is the output from the 5V regulator (when DC jack is used), or from

• USB. It can supply ~500mA peak from USB and ~800mA peak from DC GND - this is the common ground for all power and logic

• Vin - this is the higher of the DC jack or USB voltage. So if the DC jack is

• plugged in and 9V, Vin is 9V. If only USB connected, this will be 5V.

There is also an on/off switch. This switch is only for the DC jack and does not affect powering via USB

©Adafruit Industries Page 14 of 238

Logic pins

This is the general purpose I/O pin set for the microcontroller. All logic is 3.3V Most pins can do PWM output All pins except D4 can be interrupt inputs

Top Row

#0 / RX - GPIO #0, also receive (input) pin for Serial1 (hardware UART)

• #1 / TX - GPIO #1, also transmit (output) pin for Serial1

• #2 through #12 - These are general purpose GPIO. If there's a dot next to the

• pad it can act as a PWM output. #13 - GPIO #13 and is connected to the red LED marked L next to the USB jack

• SDA- the I2C (Wire) data pin. There's no pull up on this pin by default so when

• using with I2C, you may need a 2.2K-10K pullup. SCL - the I2C (Wire) clock pin. There's no pull up on this pin by default so when

• using with I2C, you may need a 2.2K-10K pullup.

©Adafruit Industries Page 15 of 238

Bottom Row

A0 - This pin is analog input A0 but is also an analog output due to having a

• DAC (digital-to-analog converter). You can set the raw voltage to anything from 0 to 3.3V, unlike PWM outputs this is a true analog output A1 thru A5 - These are each analog input as well as digital I/O pins.

•

Right side

SCK/MOSI/MISO - These are the

• hardware SPI pins, are are connected to the 2x3 header on the right hand side. you can use them as everyday GPIO pins (but recommend keeping them free as they are best used for hardware SPI connections for high speed.)



Additional analog inputs

In addition to the A0-A5 pins, there are extra analog inputs available

Digital #0 is also A6

• Digital #1 is also A7

• Digital #4 is also A8

• Digital #5 is also A9

• Digital #8 is also A10

• Digital #9 is also A11

•

These pins are available in CircuitPython under the board module. Names that start with # are prefixed with D and other names are as is. So #0 / RX above is available as

board.D0 and board.RX for example.

©Adafruit Industries Page 16 of 238

SPI Flash and NeoPixel

As part of the 'Express' series of boards, the Metro M0 Express is designed for use with CircuitPython. To make that easy, we have added two extra parts to this Metro M0: a mini NeoPixel (RGB LED) and a 2 MB SPI Flash chip

The NeoPixel is connected to pin #40 in Arduino, so just use our NeoPixel library(htt

ps://adafru.it/dhw) and set it up as a single-LED strand on pin 40. In CircuitPython, the

NeoPixel is board.NEOPIXEL and the library for it is here(https://adafru.it/wby) and in the bundle(https://adafru.it/uap). The NeoPixel is powered by the 3.3V power supply but that hasn't shown to make a big difference in brightness or color. The NeoPixel is also used by the bootloader to let you know if the device has enumerated correctly (green) or USB failure (red). In CircuitPython, the LED is used to indicate the runtime status.

The SPI Flash is connected to 4 pins that are not brought out on the GPIO pads. This way you don't have to worry about the SPI flash colliding with other devices on the main SPI connection. Under Arduino, the FLASH SCK pin is #38, MISO is #36, MOSI is #37, and CS is #39. If you use Metro M0 Express as your board type, you'll be able to access the Flash SPI port under SPI1 - this is a fully new hardware SPI device separate from the GPIO pins on the outside edge of the Feather. In CircuitPython, the SPI flash is used natively by the interpretter and is read-only to user code, instead the Flash just shows up as the writeable disk drive!

©Adafruit Industries Page 17 of 238

Other Pins!

RST - this is the Reset pin, tie to ground to manually reset the ATSAMD21, as

• well as launch the bootloader manually ARef - the analog reference pin. Normally the reference voltage is the same as

• the chip logic voltage (3.3V) but if you need an alternative analog reference, connect it to this pin and select the external AREF in your firmware. Can't go higher than 3.3V! IORef - the digital reference voltage pin. This reference voltage is the same as

• the chip logic voltage (3.3V) and cannot be changed.

©Adafruit Industries Page 18 of 238

Debug Interface

If you'd like to do more advanced development, trace-debugging, or not use the bootloader, we have the SWD interface exposed.

You can use any 2x5 0.05" pitch SWD interface to connect. We suggest a J-Link. Since the SWCLK pin is shared between the NeoPixel, and the bootloader takes control of the pin, you need to reset the board right before beginning debug. OpenOCD and some other debug interfaces may not be able to do this. That's why we really really suggest a JLink!

SEGGER J-Link EDU - JTAG/SWD Debugger

The SEGGER J-Link EDU is identical to the more expensive J-Link BASE model except for the terms of use.If...

https://www.adafruit.com/product/1369

©Adafruit Industries Page 19 of 238

SEGGER J-Link BASE - JTAG/SWD Debugger

The SEGGER J-Link BASE is identical to the cheaperJ-Link EDUmodel except for the terms of...

https://www.adafruit.com/product/2209

You'll need an adapter and cable to convert the 2x10 JTAG cable to SWD

JTAG (2x10 2.54mm) to SWD (2x5 1.27mm) Cable Adapter Board

This adapter board is designed for adapting a 'classic' 2x10 (0.1"/2.54mm pitch) JTAG cable to a slimmer 2x5 (0.05"/

1.27mm pitch) SWD Cable. It's helpful...

https://www.adafruit.com/product/2094

10-pin 2x5 Socket-Socket 1.27mm IDC (SWD) Cable - 150mm long

These little cables are handy when programming or debugging a tiny board that uses 10-pin 1.27mm (0.05") pitch SWD programming connectors. We see these connectors often on ARM...

https://www.adafruit.com/product/1675

UF2 Bootloader Details

This is an information page for advanced users who are curious how we get code from your computer into your Express board!

©Adafruit Industries Page 20 of 238

Adafruit SAMD21 (M0) and SAMD51 (M4) boards feature an improved bootloader that makes it easier than ever to flash different code onto the microcontroller. This bootloader makes it easy to switch between Microsoft MakeCode, CircuitPython and Arduino.

Instead of needing drivers or a separate program for flashing (say, bossac , jlink or avrdude ), one can simply drag a file onto a removable drive.

The format of the file is a little special. Due to 'operating system woes' you cannot just drag a binary or hex file (trust us, we tried it, it isn't cross-platform compatible). Instead, the format of the file has extra information to help the bootloader know where the data goes. The format is calledUF2 (USB Flashing Format). Microsoft MakeCode generates UF2s for flashing and CircuitPython releases are also available as UF2. You can also create your own UF2s from binary files using uf2tool, available

here.(https://adafru.it/vPE)

The bootloader is also BOSSA compatible, so it can be used with the Arduino IDE which expects a BOSSA bootloader on ATSAMD-based boards

For more information about UF2, you can read a bunch more at the MakeCode blog(h

ttps://adafru.it/w5A), then check out the UF2 file format specification.(https:// adafru.it/vPE)

Visit Adafruit's fork of the Microsoft UF2-samd bootloader GitHub repository(https://

adafru.it/Beu) for source code andreleases of pre-built bootloaders on CircuitPython.

org(https://adafru.it/Em8).

The bootloader is not needed when changing your CircuitPython code. Its only needed when upgrading the CircuitPython core or changing between CircuitPython, Arduino and Microsoft MakeCode.

©Adafruit Industries Page 21 of 238

Entering Bootloader Mode

The first step to loading new code onto your board is triggering the bootloader. It is easily done by double tapping the reset button. Once the bootloader is active you will see the small red LED fade in and out and a new drive will appear on your computer with a name ending in BOOT. For example, feathers show up as FEATHERBOOT, while the new CircuitPlayground shows up as CPLAYBOOT, Trinket M0 will show up as TRINKETBOOT, and Gemma M0 will show up as GEMMABOOT

Furthermore, when the bootloader is active, it will change the color of one or more onboard neopixels to indicate the connection status, red for disconnected and green for connected. If the board is plugged in but still showing that its disconnected, try a different USB cable. Some cables only provide power with no communication.

For example, here is a Feather M0 Express running a colorful Neopixel swirl. When the reset button is double clicked (about half second between each click) the NeoPixel will stay green to let you know the bootloader is active. When the reset button is clicked once, the 'user program' (NeoPixel color swirl) restarts.

©Adafruit Industries Page 22 of 238

If the bootloader couldn't start, you will get a red NeoPixel LED.

That could mean that your USB cable is no good, it isn't connected to a computer, or maybe the drivers could not enumerate. Try a new USB cable first. Then try another port on your computer!

Once the bootloader is running, check your computer. You should see a USB Disk drive...

©Adafruit Industries Page 23 of 238

Once the bootloader is successfully connected you can open the drive and browse the virtual filesystem. This isn't the same filesystem as you use with CircuitPython or Arduino. It should have three files:

CURRENT.UF2 - The current contents of the microcontroller flash.

• INDEX.HTM - Links to Microsoft MakeCode.

• INFO_UF2.TXT - Includes bootloader version info. Please include it on bug

• reports.

Using the Mass Storage Bootloader

To flash something new, simply drag any UF2 onto the drive. After the file is finished copying, the bootloader will automatically restart. This usually causes a warning about an unsafe eject of the drive. However, its not a problem. The bootloader knows when everything is copied successfully.

©Adafruit Industries Page 24 of 238

You may get an alert from the OS that the file is being copied without it's properties. You can just click Yes

You may also get get a complaint that the drive was ejected without warning. Don't worry about this. The drive only ejects once the bootloader has verified and completed the process of writing the new code

Using the BOSSA Bootloader

As mentioned before, the bootloader is also compatible with BOSSA, which is the standard method of updating boards when in the Arduino IDE. It is a command-line tool that can be used in any operating system. We won't cover the full use of the bos sac tool, suffice to say it can do quite a bit! More information is available at ShumaTec

h(https://adafru.it/vQa).

©Adafruit Industries Page 25 of 238

Windows 7 Drivers

If you are running Windows 7 (or, goodness, something earlier?) You will need a Serial Port driver file. Windows 10 users do not need this so skip this step.

You can download our full driver package here:

Download Latest Adafruit Driver

Installer

https://adafru.it/AB0

Download and run the installer. We recommend just selecting all the serial port drivers available (no harm to do so) and installing them.

Verifying Serial Port in Device Manager

If you're running Windows, its a good idea to verify the device showed up. Open your Device Manager from the control panel and look under Ports (COM & LPT) for a device called Feather M0 or Circuit Playground or whatever!

©Adafruit Industries Page 26 of 238

If you see something like this, it means you did not install the drivers. Go back and try again, then remove and re-plug the USB cable for your board

©Adafruit Industries Page 27 of 238

Running bossac on the command line

If you are using the Arduino IDE, this step is not required. But sometimes you want to read/write custom binary files, say for loading CircuitPython or your own code. We recommend using bossac v 1.7.0 (or greater), which has been tested. The Arduino

branch is most recommended(https://adafru.it/vQb).

You can download the latest builds here.(https://adafru.it/s1B) The mingw32 version

is for Windows, apple-darwin for Mac OSX and various linux options for Linux. Once downloaded, extract the files from the zip and open the command line to the directory with bossac .

With bossac versions 1.9 or later, you must use the --offset parameter on the command line, and it must have the correct value for your board.

With bossac version 1.9 or later, you must give an --offset parameter on the command line to specify where to start writing the firmware in flash memory.This

©Adafruit Industries Page 28 of 238

parameter was added in bossac 1.8.0 with a default of 0x2000 , but starting in 1.9, the default offset was changed to 0x0000 , which is not what you want in most cases. If you omit the argument for bossac 1.9 or later, you will probably see a "Verify Failed" error from bossac. Remember to change the option for -p or --port to match the port on your Mac.

Replace the filename below with the name of your downloaded .bin :it will vary based on your board!

Using bossac Versions 1.7.0, 1.8

There is no --offset parameter available. Use a command line like this:

bossac -p=/dev/cu.usbmodem14301 -e -w -v -R adafruit-circuitpython-bo

ardname-version.bin

For example,

bossac -p=/dev/cu.usbmodem14301 -e -w -v -R adafruit-circuitpython-

feather_m0_express-3.0.0.bin

Using bossac Versions 1.9 or Later

For M0 boards, which have an 8kB bootloader, you must specify -offset=0x2000 , for example:

bossac -p=/dev/cu.usbmodem14301 -e -w -v -R --offset=0x2000 adafruit-

circuitpython-feather_m0_express-3.0.0.bin

For M4 boards, which have a 16kB bootloader, you must specify -offset=0x4000 , for example:

bossac -p=/dev/cu.usbmodem14301 -e -w -v -R --offset=0x4000 adafruit-

circuitpython-feather_m4_express-3.0.0.bin

This will e rase the chip, w rite the given file, v erify the write and R eset the board. On Linux or MacOS you may need to run this command with sudo ./bossac ... , or add yourself to thedialoutgroup first.

©Adafruit Industries Page 29 of 238

Updating the bootloader

The UF2 bootloader is relatively new and while we've done a ton of testing, it may contain bugs. Usually these bugs effect reliability rather than fully preventing the bootloader from working. If the bootloader is flaky then you can try updating the bootloader itself to potentially improve reliability.

If you're using MakeCode on a Mac, you need to make sure to upload the bootloader to avoid a serious problem with newer versions of MacOS. See instructions and more details here(https://adafru.it/ECU).

In general, you shouldn't have to update the bootloader! If you do think you're having bootloader related issues, please post in the forums or discord.

Updating the bootloader is as easy as flashing CircuitPython, Arduino or MakeCode. Simply enter the bootloader as above and then drag the update bootloader uf2 file below. This uf2 contains a program which will unlock the bootloader section, update the bootloader, and re-lock it. It will overwrite your existing code such as CircuitPython or Arduino so make sure everything is backed up!

After the file is copied over, the bootloader will be updated and appear again. The IN FO_UF2.TXT file should show the newer version number inside.

For example:

UF2 Bootloader v2.0.0-adafruit.5 SFHWRO Model: Metro M0 Board-ID: SAMD21G18A-Metro-v0

Lastly, reload your code from Arduino or MakeCode or flash the latest CircuitPython

core(https://adafru.it/Em8).

©Adafruit Industries Page 30 of 238

Below are the latest updaters for various boards. The latest versions can always be found here(https://adafru.it/Bmg). Look for the update-bootloader... files, not the bootloader... files.

Circuit Playground Express V3.7.0

update-bootloader.uf2

https://adafru.it/JcN

Feather M0 Express v3.7.0 update-

bootloader.uf2

https://adafru.it/JcO

Metro M0 Express v3.7.0 update-

bootloader.uf2

https://adafru.it/JcR

Gemma M0 v3.7.0 update-

bootloader.uf2

https://adafru.it/JcU

Trinket M0 v3.7.0 update-

bootloader.uf2

https://adafru.it/JcX

Itsy Bitsy M0 v3.7.0 update-

bootloader.uf2

https://adafru.it/Jc-

Grand Central M4 v3.7.0 update-

bootloader.uf2

https://adafru.it/Jd2

Latest version of update-

bootloader.uf2 for other boards.

Make sure you pick the right one.

https://adafru.it/Bmg

©Adafruit Industries Page 31 of 238

Getting Rid of Windows Pop-ups

If you do a lot of development on Windows with the UF2 bootloader, you may get annoyed by the constant "Hey you inserted a drive what do you want to do" pop-ups.

Go to the Control Panel. Click on the Hardware and Sound header

Click on the Autoplay header

Uncheck the box at the top, labeled Use Autoplay for all devices

©Adafruit Industries Page 32 of 238

Making your own UF2

Making your own UF2 is easy! All you need is a .bin file of a program you wish to flash and the Python conversion script(https://adafru.it/vZb). Make sure that your program was compiled to start at 0x2000 (8k) for M0 boards or 0x4000 (16kB) for M4 boards. The bootloader takes up the first 8kB (M0) or 16kB (M4). CircuitPython's linker script(h

ttps://adafru.it/CXh) is an example on how to do that.

Once you have a .bin file, you simply need to run the Python conversion script over it. Here is an example from the directory with uf2conv.py. This command will produce a f irmware.uf2 file in the same directory as the source firmware.bin. The uf2 can then be flashed in the same way as above.

# For programs with 0x2000 offset (default) uf2conv.py -c -o build-circuitplayground_express/firmware.uf2 buildcircuitplayground_express/firmware.bin

# For programs needing 0x4000 offset (M4 boards) uf2conv.py -c -b 0x4000 -o build-metro_m4_express/firmware.uf2 buildmetro_M4_express/firmware.bin

Installing the bootloader on a fresh/bricked board

If you somehow damaged your bootloader or maybe you have a new board, you can use a JLink to re-install it.

Here's a Learn Guide explaining how to fix the bootloader on a variety of boards using Atmel Studio(https://adafru.it/F5f)

Here's a short writeup by turbinenreiter on how to do it for the Feather M4 (but adaptable to other boards)(https://adafru.it/ven)

Arduino IDE Setup

The first thing you will need to do is to download the latest release of the Arduino IDE. You will need tobe using version 1.8 or higher for this guide

Arduino IDE Download

https://adafru.it/f1P

©Adafruit Industries Page 33 of 238

After you have downloaded and installed the latest version of Arduino IDE, you will need to start the IDEand navigate tothe Preferences menu. You can access it from the File menu in Windows or Linux, or the Arduino menu on OS X.

A dialog will pop up just like the one shown below.

We will be adding a URL to the new Additional Boards Manager URLs option. The list of URLs is comma separated, and you will only have to add eachURL once.New Adafruit boards and updates to existing boardswill automatically be picked upby the

©Adafruit Industries Page 34 of 238

Board Manager each timeit is opened. The URLs point to index files that the Board Manager uses to build the list of available & installed boards.

To find the most up to date list of URLs you canadd, you can visit the list of third party

board URLs on the Arduino IDE wiki(https://adafru.it/f7U). We will only need to add

one URL to the IDE in this example, but you can add multiple URLS by separating them with commas. Copy and paste the link below into theAdditional Boards Manager URLs option in the Arduino IDE preferences.

https://adafruit.github.io/arduino-board-index/ package_adafruit_index.json

Here's a short description of each of the Adafruit supplied packages that will be available in the Board Manager when you add the URL:

Adafruit AVR Boards - Includes support for Flora, Gemma, Feather 32u4,

• ItsyBitsy 32u4, Trinket, & Trinket Pro. Adafruit SAMD Boards - Includes support for Feather M0 and M4, Metro M0 and

• M4, ItsyBitsy M0 and M4, Circuit Playground Express, Gemma M0 and Trinket M0 Arduino Leonardo & Micro MIDI-USB - This adds MIDI over USB support for the

• Flora, Feather 32u4, Micro and Leonardo using the arcore project(https://

adafru.it/eSI).

If you have multiple boards you want to support, say ESP8266 and Adafruit, have both URLs in the text box separated by a comma (,)

©Adafruit Industries Page 35 of 238

Once done click OK to save the new preference settings. Next we will look at installing boards with the Board Manager.

Now continue to the next step to actually install the board support package!

Using with Arduino IDE

The Feather/Metro/Gemma/QTPy/Trinket M0 and M4 use an ATSAMD21 or ATSAMD51 chip, and you can pretty easily get it working with the Arduino IDE. Most libraries (including the popular ones like NeoPixels and display) will work with the M0 and M4, especially devices & sensors that use I2C or SPI.

Now that you have added the appropriate URLs to the Arduino IDE preferences in the previous page, you can open the Boards Manager by navigating to the Tools->Board menu.

Once the Board Manager opens, click on the category drop down menu on the top left hand side of the window and select All. You will then be able to select and install the boards suppliedby the URLs added to the preferences.

Remember you need SETUP the Arduino IDE to support our board packages see the previous page on how to add adafruit's URL to the preferences

Install SAMD Support

First up, install the latest Arduino SAMD Boards (version 1.6.11or later)

You can type Arduino SAMD in the top search bar, then when you see the entry, click I nstall

©Adafruit Industries Page 36 of 238

Install Adafruit SAMD

Next you can install the Adafruit SAMD package to add the board file definitions

Make sure you have Type All selected to the left of the Filter your search... box

You can type Adafruit SAMD in the top search bar, then when you see the entry, click I nstall

Even though in theory you don't need to - I recommend rebooting the IDE

Quit and reopenthe Arduino IDE to ensure that all of the boards are properly installed. You should now be able to select and upload to the new boards listed in the Tools->Board menu.

©Adafruit Industries Page 37 of 238

Select the matching board, the current options are:

Feather M0 (for use with any Feather M0 other than the Express)

• Feather M0 Express

• Metro M0 Express

• Circuit Playground Express

• Gemma M0

• Trinket M0

• QT Py M0

• ItsyBitsy M0

• Hallowing M0

• Crickit M0 (this is for direct programming of the Crickit, which is probably not

• what you want! For advanced hacking only) Metro M4 Express

• Grand Central M4 Express

• ItsyBitsy M4 Express

• Feather M4 Express

• Trellis M4 Express

• PyPortal M4

• PyPortal M4 Titano

• PyBadge M4 Express

• Metro M4 Airlift Lite

• PyGamer M4 Express

• MONSTER M4SK

• Hallowing M4

• MatrixPortal M4

• BLM Badge

•

Install Drivers (Windows 7 & 8 Only)

When you plug in the board, you'll need to possibly install a driver

©Adafruit Industries Page 38 of 238

Click below to download our Driver Installer

Download Latest Adafruit Drivers

package

https://adafru.it/mb8

Download and run the installer

Run the installer! Since we bundle the SiLabs and FTDI drivers as well, you'll need to click through the license

Select which drivers you want to install, the defaults will set you up with just about every Adafruit board!

©Adafruit Industries Page 39 of 238

Click Install to do the installin'

Blink

Now you can upload your first blink sketch!

Plug in the M0 or M4 board, and wait for it to be recognized by the OS (just takes a few seconds). It will create a serial/COM port, you can now select it from the dropdown, it'll even be 'indicated' as Trinket/Gemma/Metro/Feather/ItsyBitsy/Trellis!

©Adafruit Industries Page 40 of 238

Please note, the QT Py and Trellis M4 Express are two of our very few boards that does not have an onboard pin 13 LED so you can follow this section to practice uploading but you wont see an LED blink!

Now load up the Blink example

// the setup function runs once when you press reset or power the board void setup() { // initialize digital pin 13 as an output. pinMode(13, OUTPUT); }

// the loop function runs over and over again forever void loop() { digitalWrite(13, HIGH); // turn the LED on (HIGH is the voltage level) delay(1000); // wait for a second digitalWrite(13, LOW); // turn the LED off by making the voltage LOW delay(1000); // wait for a second }

And click upload! That's it, you will be able to see the LED blink rate change as you adapt the delay() calls.

If you are having issues, make sure you selected the matching Board in the menu that matches the hardware you have in your hand.

Successful Upload

If you have a successful upload, you'll get a bunch of red text that tells you that the device was found and it was programmed, verified & reset

©Adafruit Industries Page 41 of 238

After uploading, you may see a message saying "Disk NotEjectedProperly" about the ...BOOT drive. You can ignore that message: it's an artifact of how the bootloader and uploading work.

Compilation Issues

If you get an alert that looks like

Cannot run program "{runtime.tools.arm-none-eabi-gcc.path}\bin\arm-non-eabi-g++"

Make sure you have installed the Arduino SAMD boards package, you need both Ard uino & Adafruit SAMD board packages

©Adafruit Industries Page 42 of 238

Manually bootloading

If you ever get in a 'weird' spot with the bootloader, or you have uploaded code that crashes and doesn't auto-reboot into the bootloader, click the RST button twice (like a double-click)to get back into the bootloader.

The red LED will pulse and/or RGB LED will be green, so you know that its in bootloader mode.

Once it is in bootloader mode, you can select the newly created COM/Serial port and re-try uploading.

You may need to go back and reselect the 'normal' USB serial port next time you want to use the normal upload.

Ubuntu& Linux Issue Fix

Follow the steps for installing Adafruit's udev rules on this page.(https://adafru.it/iOE)

Adapting Sketches to M0 & M4

The ATSAMD21 and 51 are very nice little chips, but fairly new as Arduino-compatible cores go. Most sketches & libraries will work but here’s a collection of things we noticed.

The notes below cover a range of Adafruit M0 and M4 boards, but not every rule will apply to every board (e.g. Trinket and Gemma M0 do not have ARef, so you can skip the Analog References note!).

©Adafruit Industries Page 43 of 238

Analog References

If you'd like to use the ARef pin for a non-3.3V analog reference, the code to use is

analogReference(AR_EXTERNAL) (it's AR_EXTERNAL not EXTERNAL)

Pin Outputs & Pullups

The old-style way of turning on a pin as an input with a pullup is to use

pinMode(pin, INPUT) digitalWrite(pin, HIGH)

This is because the pullup-selection register on 8-bit AVR chips is the same as the output-selection register.

For M0 & M4 boards, you can't do this anymore! Instead, use:

pinMode(pin, INPUT_PULLUP)

Code written this way still has the benefit of being backwards compatible with AVR. You don’t need separate versions for the different board types.

Serial vs SerialUSB

99.9% of your existing Arduino sketches use Serial.print to debug and give output. For the Official Arduino SAMD/M0 core, this goes to the Serial5 port, which isn't exposed on the Feather. The USB port for the Official Arduino M0 core is called SerialUSB instead.

In the Adafruit M0/M4 Core, we fixed it so that Serial goes to USB so it will automatically work just fine.

However, on the off chance you are using the official Arduino SAMD core and not the Adafruit version (which really, we recommend you use our version because it’s been tuned to our boards), and you want your Serial prints and reads to use the USB port, use SerialUSB instead of Serial in your sketch.

©Adafruit Industries Page 44 of 238

If you have existing sketches and code and you want them to work with the M0 without a huge find-replace, put

#if defined(ARDUINO_SAMD_ZERO) && defined(SERIAL_PORT_USBVIRTUAL)

 // Required for Serial on Zero based boards  #define Serial SERIAL_PORT_USBVIRTUAL #endif

right above the first function definition in your code. For example:

AnalogWrite / PWM on Feather/Metro M0

After looking through the SAMD21 datasheet, we've found that some of the options listed in the multiplexer table don't exist on the specific chip used in the Feather M0.

For all SAMD21 chips, there are two peripherals that can generate PWM signals: The Timer/Counter (TC) and Timer/Counter for Control Applications (TCC). Each SAMD21 has multiple copies of each, called 'instances'.

Each TC instance has one count register, one control register, and two output channels. Either channel can be enabled and disabled, and either channel can be inverted. The pins connected to a TC instance can output identical versions of the same PWM waveform, or complementary waveforms.

Each TCC instance has a single count register, but multiple compare registers and output channels. There are options for different kinds of waveform, interleaved switching, programmable dead time, and so on.

The biggest members of the SAMD21 family have five TC instances with two 'waveform output' (WO) channels, and three TCC instances with eight WO channels:

TC[0-4],WO[0-1]

•

©Adafruit Industries Page 45 of 238

TCC[0-2],WO[0-7]

•

And those are the onesshown in the datasheet's multiplexer tables.

The SAMD21G used in the Feather M0 only has three TC instances with two output channels, and three TCC instances with eightoutput channels:

TC[3-5],WO[0-1]

• TCC[0-2],WO[0-7]

•

Tracing the signals to the pins broken out on the Feather M0, the following pins can't do PWM at all:

Analog pin A5

•

The following pins can be configured for PWM without any signal conflicts as long as the SPI, I2C, and UART pins keep their protocol functions:

Digital pins 5, 6, 9, 10, 11, 12, and 13

• Analog pins A3 and A4

•

If only the SPI pins keep their protocol functions, you can also do PWM on the following pins:

TX and SDA (Digital pins 1 and 20)

•

analogWrite() PWM range

On AVR, if you set a pin's PWM with analogWrite(pin, 255) it will turn the pin fully HIGH. On the ARM cortex, it will set it to be 255/256 so there will be very slim but still-existing pulses-to-0V. If you need the pin to be fully on, add test code that checks if you are trying to analogWrite(pin, 255) and, instead, does a digitalWrite(p

in, HIGH)

©Adafruit Industries Page 46 of 238

analogWrite() DAC on A0

If you are trying to use analogWrite() to control the DAC output on A0, make sure you do not have a line that sets the pin to output. Remove: pinMode(A0, OUTPUT) .

Missing header files

There might be code that uses libraries that are not supported by the M0 core. For example if you have a line with

#include <util/delay.h>

you'll get an error that says

fatal error: util/delay.h: No such file or directory  #include <util/delay.h>             ^ compilation terminated. Error compiling.

In which case you can simply locate where the line is (the error will give you the file name and line number) and 'wrap it' with #ifdef's so it looks like:

#if !defined(ARDUINO_ARCH_SAM) && !defined(ARDUINO_ARCH_SAMD) && ! defined(ESP8266) && !defined(ARDUINO_ARCH_STM32F2) #include <util/delay.h> #endif

The above will also make sure that header file isn't included for other architectures

If the #include is in the arduino sketch itself, you can try just removing the line.

Bootloader Launching

For most other AVRs, clicking reset while plugged into USB will launch the bootloader manually, the bootloader will time out after a few seconds. For the M0/M4, you'll need to double click the button. You will see a pulsing red LED to let you know you're in bootloader mode. Once in that mode, it wont time out! Click reset again if you want to go back to launching code.

©Adafruit Industries Page 47 of 238

Aligned Memory Access

This is a little less likely to happen to you but it happened to me! If you're used to 8bit platforms, you can do this nice thing where you can typecast variables around. e.g.

uint8_t mybuffer[4];

float f = (float)mybuffer;

You can't be guaranteed that this will work on a 32-bit platform because mybuffer might not be aligned to a 2 or 4-byte boundary. The ARM Cortex-M0 can only directly access data on 16-bit boundaries (every 2 or 4 bytes). Trying to access an oddboundary byte (on a 1 or 3 byte location) will cause a Hard Fault and stop the MCU. Thankfully, there's an easy work around ... just use memcpy!

uint8_t mybuffer[4]; float f; memcpy(&f, mybuffer, 4)

Floating Point Conversion

Like the AVRArduinos, the M0 library does not have full support for converting floating point numbers to ASCII strings. Functions like sprintf will not convert floating point. Fortunately, the standard AVR-LIBC library includes the dtostrf function which can handle the conversion for you.

Unfortunately, the M0 run-time library does not have dtostrf. You may see some references to using #include <avr/dtostrf.h> to get dtostrf in your code. And while it will compile, it does not work.

Instead, check out this thread to find a working dtostrffunction you can include in your code:

http://forum.arduino.cc/index.php?topic=368720.0(https://adafru.it/lFS)

How Much RAM Available?

The ATSAMD21G18 has 32K of RAM, but you still might need to track it for some reason. You can do so with this handy function:

©Adafruit Industries Page 48 of 238

extern "C" char *sbrk(int i);

int FreeRam () { char stack_dummy = 0; return &stack_dummy - sbrk(0); }

Thx to http://forum.arduino.cc/index.php?topic=365830.msg2542879#msg2542879(h

ttps://adafru.it/m6D) for the tip!

Storing data in FLASH

If you're used to AVR, you've probably used PROGMEM to let the compiler know you'd like to put a variable or string in flash memory to save on RAM. On the ARM, its a little easier, simply add const before the variable name:

const char str[] = "My very long string";

That string is now in FLASH. You can manipulate the string just like RAM data, the compiler will automatically read from FLASH so you dont need special progmemknowledgeable functions.

You can verify where data is stored by printing out the address: Serial.print("Address of str $"); Serial.println((int)&str, HEX);

If the address is $2000000 or larger, its in SRAM. If the address is between $0000 and $3FFFF Then it is in FLASH

Pretty-Printing out registers

There's a lot of registers on the SAMD21, and you often are going through ASF or another framework to get to them. So having a way to see exactly what's going on is handy. This library from drewfish will help a ton!

https://github.com/drewfish/arduino-ZeroRegs(https://adafru.it/Bet)

©Adafruit Industries Page 49 of 238

M4 Performance Options

As of version 1.4.0 of the Adafruit SAMD Boards package in the Arduino Boards Manager, some options are available to wring extra performance out of M4-based devices. These are in the Tools menu.

All of these performance tweaks involve a degree of uncertainty. There’s no guarantee of improved performance in any given project, and some may even be detrimental, failing to work in part or in whole. If you encounter trouble, select the default performance settings and re-upload.

Here’s what you get and some issues you might encounter…

CPU Speed (overclocking)

This option lets you adjust the microcontroller core clock…the speed at which it processes instructions…beyond the official datasheet specifications.

Manufacturers often rate speeds conservatively because such devices are marketed for harsh industrial environments…if a system crashes, someone could lose a limb or worse. But most creative tasks are less critical and operate in more comfortable settings, and we can push things a bit if we want more speed.

There is a small but nonzero chance of code locking up or failing to run entirely. If this happens, try dialing back the speed by one notch and re-upload, see if it’s more stable.

Much more likely, some code or libraries may not play well with the nonstandard CPU speed. For example, currently the NeoPixel library assumes a 120 MHz CPU speed and won’t issue the correct data at other settings (this will be worked on). Other

©Adafruit Industries Page 50 of 238

libraries may exhibit similar problems, usually anything that strictly depends on CPU timing…you might encounter problems with audio- or servo-related code depending how it’s written. If you encounter such code or libraries, set the CPU speed to the default 120 MHz and re-upload.

Optimize

There’s usually more than one way to solve a problem, some more resource-intensive than others. Since Arduino got its start on resource-limited AVR microcontrollers, the C++ compiler has always aimed for the smallest compiled program size. The “Optimize” menu gives some choices for the compiler to take different and often faster approaches, at the expense of slightly larger program size…with the huge flash memory capacity of M4 devices, that’s rarely a problem now.

The “Small” setting will compile your code like it always has in the past, aiming for the smallest compiled program size.

The “Fast” setting invokes various speed optimizations. The resulting program should produce the same results, is slightly larger, and usually (but not always) noticably faster. It’s worth a shot!

“Here be dragons” invokes some more intensive optimizations…code will be larger still, faster still, but there’s a possibility these optimizations could cause unexpected behaviors. Some code may not work the same as before. Hence the name. Maybe you’ll discover treasure here, or maybe you’ll sail right off the edge of the world.

Most code and libraries will continue to function regardless of the optimizer settings. If you do encounter problems, dial it back one notch and re-upload.

Cache

This option allows a small collection of instructions and data to be accessed more quickly than from flash memory, boosting performance. It’s enabled by default and should work fine with all code and libraries. But if you encounter some esoteric situation, the cache can be disabled, then recompile and upload.

Max SPI and Max QSPI

These should probably be left at their defaults. They’re present mostly for our own experiments and can cause serious headaches.

©Adafruit Industries Page 51 of 238

Max SPI determines the clock source for the M4’s SPI peripherals. Under normal circumstances this allows transfers up to 24 MHz, and should usually be left at that setting. But…if you’re using write-only SPI devices (such as TFT or OLED displays), this option lets you drive them faster (we’ve successfully used 60 MHz with some TFT screens). The caveat is, if using any read/write devices (such as an SD card), this will not work at all…SPI readsabsolutely max out at the default 24 MHz setting, and anything else will fail. Write = OK. Read = FAIL. This is true even if your code is using a lower bitrate setting…just having the different clock source prevents SPI reads.

Max QSPI does similarly for the extra flash storage on M4 “Express” boards. Very few Arduino sketches access this storage at all, let alone in a bandwidth-constrained context, so this will benefit next to nobody. Additionally, due to the way clock dividers are selected, this will only provide some benefit when certain “CPU Speed” settings are active. Our PyPortal Animated GIF Display(https://adafru.it/EkO) runs marginally better with it, if using the QSPI flash.

Enabling the Buck Converter on some M4 Boards

If you want to reduce power draw, some of our boards have an inductor so you can use the 1.8V buck converter instead of the built in linear regulator. If the board does have an inductor (see the schematic) you can add the line SUPC->VREG.bit.SEL =

1; to your code to switch to it. Note it will make ADC/DAC reads a bit noisier so we

don't use it by default. You'll save ~4mA(https://adafru.it/F0H).

Using SPI Flash

One of the bestfeatures of the M0 express board is a small SPI flash memory chip built into the board. This memory can be used for almost any purpose like storingdata files, Python code, and more. Think of it like a little SD card that is always connected to the board, and in fact with Arduino you can access the memory using a library that is very similar to the Arduino SD card library(https://adafru.it/ucu). You can even read and write files that CircuitPython stores on the flash chip!

To use the flash memory with Arduino you'll need to install the Adafruit SPI Flash

Memory library(https://adafru.it/wbt) in the Arduino IDE.

Open up the Arduino library manager

©Adafruit Industries Page 52 of 238

Search for theAdafruit SPIFlashlibrary and install it

Search for the SdFat - Adafruit Forklibrary and install it

We also have a great tutorial on Arduino library installation at:

http://learn.adafruit.com/adafruit-all-about-arduino-libraries-install-use(https://

adafru.it/aYM)



Once the library is installed look for the following examples in the library:

fatfs_circuitpython

• fatfs_datalogging

• fatfs_format

• fatfs_full_usage

• fatfs_print_file

• flash_erase

•

These examples allow you to format the flash memory with a FAT filesystem (the same kind of filesystem used on SD cards) and read and write files to it just like a SD card.

©Adafruit Industries Page 53 of 238

Read & Write CircuitPython Files

The fatfs_circuitpython example shows how to read and write files on the flash chip so that they're accessible from CircuitPython. This means you can run a CircuitPython program on your board and have it store data, then run an Arduino sketch that uses this library to interact with the same data.

Note that before you use the fatfs_circuitpython example you must have loaded CircuitPython on your board. Load the latest version of CircuitPython as explained in

this guide(https://adafru.it/BeN) first to ensure a CircuitPython filesystem is initialized

and written to the flash chip. Once you've loaded CircuitPython then you can run the fatfs_circuitpython example sketch.

To run the sketch load it in the Arduino IDE and upload it to the Feather/Metro/ ItsyBitsy M0 board. Then open the serial monitor at 115200 baud. You should see the serial monitor display messages as it attempts to read files and write to a file on the flash chip. Specifically the example will look for a boot.py and main.py file (like what CircuitPython runs when it starts) and print out their contents. Then it will add a line to the end of a data.txt file on the board (creating it if it doesn't exist already). After running the sketch you canreload CircuitPython on the board and open the data.txt file to read itfrom CircuitPython!

To understand how to read & write files that are compatible with CircuitPython let's examine the sketch code. First notice an instance of the Adafruit_M0_Express_Circu itPython class is created and passed an instance of the flash chip class in the last line below:

#define FLASH_SS SS1 // Flash chip SS pin. #define FLASH_SPI_PORT SPI1 // What SPI port is Flash on?

Adafruit_SPIFlash flash(FLASH_SS, &FLASH_SPI_PORT); // Use hardware SPI

// Alternatively you can define and use non-SPI pins! //Adafruit_SPIFlash flash(SCK1, MISO1, MOSI1, FLASH_SS);

// Finally create an Adafruit_M0_Express_CircuitPython object which gives // an SD card-like interface to interacting with files stored in CircuitPython's // flash filesystem. Adafruit_M0_Express_CircuitPython pythonfs(flash);

By using this Adafruit_M0_Express_CircuitPython class you'll get a filesystem object that is compatible with reading and writing files on a CircuitPython-formatted flash chip. This is very important for interoperability between CircuitPython and Arduino as CircuitPython has specialized partitioning and flash memory layoutthat isn't compatible with simpler uses of the library (shown in the other examples).

©Adafruit Industries Page 54 of 238

Once an instance of the Adafruit_M0_Express_CircuitPython class is created (called p ythonfs in this sketch) you can go on to interact with it just like if it were the SD card

library in Arduino(https://adafru.it/wbw). You can open files for reading & writing,

create directories, delete files and directories and more. Here's how the sketch checks if a boot.py file exists and prints it out a character at a time:

// Check if a boot.py exists and print it out. if (pythonfs.exists("boot.py")) { File bootPy = pythonfs.open("boot.py", FILE_READ); Serial.println("Printing boot.py..."); while (bootPy.available()) { char c = bootPy.read(); Serial.print(c); } Serial.println(); } else { Serial.println("No boot.py found..."); }

Notice the exists function is called to check if the boot.py file is found, and then the o pen function is used to open it in read mode. Once a file is opened you'll get a reference to a File class object which you can read and write from as if it were a Serial device (again just like the SD card library, all of the same File classfunctions are

available(https://adafru.it/wbw)). In this case the available function will return the

number of bytes left to read in the file, and the read function will read a character at a time to print it to the serial monitor.

Writing a file is just as easy, here's how the sketch writes to data.txt:

// Create or append to a data.txt file and add a new line // to the end of it. CircuitPython code can later open and // see this file too! File data = pythonfs.open("data.txt", FILE_WRITE); if (data) { // Write a new line to the file: data.println("Hello CircuitPython from Arduino!"); data.close(); // See the other fatfs examples like fatfs_full_usage and fatfs_datalogging // for more examples of interacting with files. Serial.println("Wrote a new line to the end of data.txt!"); } else { Serial.println("Error, failed to open data file for writing!"); }

Again the open function is used but this time it's told to open the file for writing. In this mode the file will be opened for appending (i.e. data added to the end of it) if it exists, or it will be created if it doesn't exist. Once the file is open print functions like print and println can be used to write data to the file ( just like writing to the serial monitor). Be sure to close the file when finished writing!

©Adafruit Industries Page 55 of 238

That's all there is to basic file reading and writing. Check out the fatfs_full_usage example for examples of even more functions like creating directories, deleting files & directories, checking the size of files, and more! Remember though to interact with CircuitPython files you need to use the Adafruit_Feather_M0_CircuitPython class as shown in the fatfs_circuitpython example above!

Format Flash Memory

The fatfs_format example will format the SPI flash with a new blank filesystem. Be warned this sketch will delete all data on the flash memory, including any Python code or other data you might have stored! The format sketch is useful if you'd like to wipe everything away and start fresh, or to help get back in agood state if the memory should get corrupted for some reason.

Be aware too the fatfs_format and examples below are not compatible with a CircuitPython-formatted flash chip! If you need to share data between Arduino & CircuitPython check out the fatfs_circuitpython example above.

To run the format sketch load it in the Arduino IDE and upload it to the M0 board. Then open the serial monitor at 115200 baud. You should see the serial monitor display a message asking you to confirmformatting the flash. If you don't see this message then close the serial monitor, press the board's reset button, and open the serial monitor again.

Type OK and press enter in the serial monitor input to confirm that you'd like to format the flash memory. You need to enter OK in all capital letters! 

Once confirmed the sketch will format the flash memory. The format process takes about a minute so be patient as the data is erased and formatted. You should see a

©Adafruit Industries Page 56 of 238

message printed once the format process is complete. At this point the flash chip will beready to use with a brand new empty filesystem.

Datalogging Example

One handy use of the SPI flash is to store data, like datalogging sensor readings. The fatfs_datalogging example shows basic file writing/datalogging. Open the example in the Arduino IDE and upload it to your Feather M0 board. Then open the serial monitor at 115200 baud. You should see a message printed every minute as the sketch writes a new line of data to a file on the flash filesystem.

To understand how to write to a file look in the loop function of the sketch:

// Open the datalogging file for writing. The FILE_WRITE mode will open // the file for appending, i.e. it will add new data to the end of the file. File dataFile = fatfs.open(FILE_NAME, FILE_WRITE); // Check that the file opened successfully and write a line to it. if (dataFile) { // Take a new data reading from a sensor, etc. For this example just // make up a random number. int reading = random(0,100); // Write a line to the file. You can use all the same print functions // as if you're writing to the serial monitor. For example to write // two CSV (commas separated) values: dataFile.print("Sensor #1"); dataFile.print(","); dataFile.print(reading, DEC); dataFile.println(); // Finally close the file when done writing. This is smart to do to make // sure all the data is written to the file. dataFile.close(); Serial.println("Wrote new measurement to data file!"); }

Just like using the Arduino SD card library you create a File object by calling an open function and pointing it at the name of the file and how you'd like to open it (FILE_WR ITE mode, i.e. writing new data to the end of the file). Notice however instead of calling open on a global SD card object you're calling it on a fatfs object created earlier in the sketch (look at the top after the #define configuration values).

Once the file is opened it's simply a matter of calling print and println functions on the file object to write data inside of it. This is just like writing data to the serial monitor and you can print out text, numeric, and other types of data. Be sure to close the file when you're done writing to ensure the data is stored correctly!

©Adafruit Industries Page 57 of 238

Reading and Printing Files

The fatfs_print_file example will open a file (by default the data.csv file created by running the fatfs_datalogging example above) and print all of its contents to the serial monitor. Open the fatfs_print_file example and load it on your Feather M0 board, then open the serial monitor at 115200 baud. You should see the sketch print out the contents of data.csv (if you don't have a file called data.csv on the flash look at running the datalogging example above first).

To understand how to read data from a file look in the setupfunction of the sketch:

// Open the file for reading and check that it was successfully opened. // The FILE_READ mode will open the file for reading. File dataFile = fatfs.open(FILE_NAME, FILE_READ); if (dataFile) { // File was opened, now print out data character by character until at the // end of the file. Serial.println("Opened file, printing contents below:"); while (dataFile.available()) { // Use the read function to read the next character. // You can alternatively use other functions like readUntil, readString, etc. // See the fatfs_full_usage example for more details. char c = dataFile.read(); Serial.print(c); } }

Just like when writing data with the datalogging example you create a File object by calling the open function on a fatfs object. This time however you pass a file mode of FILE_READ which tells the filesystemyou want to read data.

After you open a file for reading you can easily check if data is available by calling the available function on the file, and then read a single character with the read function. This makes it easy to loop through all of the data in a file by checking if it's available and reading a character at a time. However there are more advanced read functions you can use too--see the fatfs_full_usage example or even the Arduino SD library

documentation(https://adafru.it/ucu) (the SPI flash library implements the same

functions).

Full Usage Example

For a more complete demonstration of reading and writing files look at the fatfs_full_ usage example. This examples uses every function in the library and demonstrates things like checking for the existence of a file, creating directories, deleting files, deleting directories,and more.

©Adafruit Industries Page 58 of 238

Remember the SPI flash library is built to have the same functions and interface as the

Arduino SD library(https://adafru.it/ucu) so if you have code or examples that store

data on a SD card they should be easy to adapt to use the SPI flash library, just create a fatfs object like in the examples above and use its open function instead of the global SD object's open function. Once you have a reference to a file all of the functions and usage should be the same between the SPI flash and SD libraries!

Accessing SPI Flash

Arduino doesn't have the ability to show up as a 'mass storage' disk drive. So instead we must use CircuitPython to do that part for us. Here's the full technique:

Start the bootloader on the Express board. Drag over the latest circuitpython uf2

• file After a moment, you should see a CIRCUITPY drive appear on your hard drive

• with boot_out.txt on it Now go to Arduino and upload the fatfs_circuitpython example sketch from the

• Adafruit SPI library. Open the serial console. It will successfully mount the filesystem and write a new line to data.txt

Back on your computer, re-start the Express board bootloader, and re-drag circu

• itpython.uf2 onto the BOOT drive to reinstall circuitpython Check the CIRCUITPY drive, you should now see data.txt which you can open to

• read!

©Adafruit Industries Page 59 of 238

Once you have your Arduino sketch working well, for datalogging, you can simplify this procedure by dragging CURRENT.UF2 off of the BOOT drive to make a backup of the current program before loading circuitpython on. Then once you've accessed the file you want, re-drag CURRENT.UF2 back onto the BOOT drive to re-install the Arduino sketch!

Metro M0 HELP!

My Metro M0 stopped working when I unplugged the USB!

A lot of our example sketches have a

while (!Serial);

line in setup(), to keep the board waiting until the USB is opened. This makes it a lot easier to debug a program because you get to see all the USB data output. If you want to run your Metro M0 without USB connectivity, delete or comment out that line

My Metro never shows up as a COM or Serial port in the Arduino IDE

A vast number of Metro 'failures' are due to charge-only USB cables

We get upwards of 5 complaints a day that turn out to be due to charge-only cables!

©Adafruit Industries Page 60 of 238

Use only a cable that you know is for data syncing

If you have any charge-only cables, cut them in half throw them out. We are serious! They tend to be low quality in general, and will only confuse you and others later, just get a good data+charge USB cable

Ack! I "did something" and now when I plug in the Metro, it doesn't show up as a device anymore so I cant upload to it or fix it...

No problem! You can 'repair' a bad code upload easily. Note that this can happen if you set a watchdog timer or sleep mode that stops USB, or any sketch that 'crashes' your Metro

Turn on verbose upload in the Arduino IDE preferences

1. Plug in Metro M0, it won't show up as a COM/serial port that's ok

2. Open up the Blink example (Examples->Basics->Blink)

3. Select the correct board in the Tools menu, e.g. Metro M0 (check your board

4. to make sure you have the right one selected!) Compile it (make sure that works)

5. Click Upload to attempt to upload the code

6. The IDE will print out a bunch of COM Ports as it tries to upload. During this

7. time, double-click the reset button, you'll see the red pulsing LED and the NeoPixel will be green that tells you its now in bootloading mode The Metro will show up as the Bootloader COM/Serial port

8. The IDE should see the bootloader COM/Serial port and upload properly

I can't get the Metro USB device to show up - I get "USB Device Malfunctioning" errors!

This seems to happen when people select the wrong board from the Arduino Boards menu.

If you have a Metro M0 (look on the board to read what it is you have) Make sure you select Metro M0 - do not use Feather M0 or Arduino Zero

I'm having problems with COM ports and my Metro M0

Theres two COM ports you can have with the M0, one is the user port and one is the bootloader port. They are not the same COM port number!

©Adafruit Industries Page 61 of 238

When you upload a new user program it will come up with a user com port, particularly if you use Serial in your user program.

If you crash your user program, or have a program that halts or otherwise fails, the user com port can disappear.

When the user COM port disappears, Arduino will not be able to automatically start the bootloader and upload new software.

So you will need to help it by performing the click-during upload procedure to restart the bootloader, and upload something that is known working like "Blink"

I don't understand why the COM port disappears, this does not happen on my Arduino UNO!

UNO-type Arduinos have a seperate serial port chip (aka "FTDI chip" or "Prolific PL2303" etc etc) which handles all serial port capability seperately than the main chip. This way if the main chip fails, you can always use the COM port.

M0 and 32u4-based Arduinos do not have a seperate chip, instead the main processor performs this task for you. It allows for a lower cost, higher power setup...but requires a little more effort since you will need to 'kick' into the bootloader manually once in a while

I'm trying to upload to my 32u4, getting "avrdude: butterfly_recv(): programmer is not responding" errors

This is likely because the bootloader is not kicking in and you are accidentally trying to upload to the wrong COM port

The best solution is what is detailed above: manually upload Blink or a similar working sketch by hand by manually launching the bootloader

I'm trying to upload to my Metro M0, and I get this error "Connecting to programmer: .avrdude: butterfly_recv(): programmer is not responding"

You probably don't have Metro M0 selected in the boards drop-down. Make sure you selected Metro M0.

©Adafruit Industries Page 62 of 238

I'm trying to upload to my Metro and i get this error "avrdude: ser_recv(): programmer is not responding"

You probably don't have Metro M0 selected in the boards drop-down. Make sure you selected Metro M0

What is CircuitPython?

CircuitPython is a programming language designed to simplify experimenting and learning to program on low-cost microcontroller boards. It makes getting started easier than ever with no upfront desktop downloads needed. Once you get your board set up, open any text editor, and get started editing code. It's that simple.

CircuitPython is based on Python

Python is the fastest growing programming language. It's taught in schools and universities. It's a high-level programming language which means it's designed to be easier to read, write and maintain. It supports modules and packages which means it's easy to reuse your code for other projects. It has a built in interpreter which means there are no extra steps, like compiling, to get your code to work. And of course, Python is Open Source Software which means it's free for anyone to use, modify or improve upon.

CircuitPython adds hardware support to all of these amazing features. If you already have Python knowledge, you can easily apply that to using CircuitPython. If you have no previous experience, it's really simple to get started!

©Adafruit Industries Page 63 of 238

Why would I use CircuitPython?

CircuitPython is designed to run on microcontroller boards. A microcontroller board is a board with a microcontroller chip that's essentially an itty-bitty all-in-one computer. The board you're holding is a microcontroller board! CircuitPython is easy to use because all you need is that little board, a USB cable, and a computer with a USB connection. But that's only the beginning.

Other reasons to use CircuitPython include:

You want to get up and running quickly. Create a file, edit your code, save the

• file, and it runs immediately. There is no compiling, no downloading and no uploading needed. You're new to programming. CircuitPython is designed with education in mind.

• It's easy to start learning how to program and you get immediate feedback from the board. Easily update your code. Since your code lives on the disk drive, you can edit it

• whenever you like, you can also keep multiple files around for easy experimentation. The serial console and REPL. These allow for live feedback from your code and

• interactive programming. File storage. The internal storage for CircuitPython makes it great for data-

• logging, playing audio clips, and otherwise interacting with files. Strong hardware support. There are many libraries and drivers for sensors,

• breakout boards and other external components. It's Python! Python is the fastest-growing programming language. It's taught in

• schools and universities. CircuitPython is almost-completely compatible with Python. It simply adds hardware support.

©Adafruit Industries Page 64 of 238

This is just the beginning. CircuitPython continues to evolve, and is constantly being updated. Adafruit welcomes and encourages feedback from the community, and incorporate it into the development of CircuitPython. That's the core of the open source concept. This makes CircuitPython better for you and everyone who uses it!

CircuitPython

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. If you are running an older version of CircuitPython, you need to update. Click the button below to download the latest!

CircuitPython(https://adafru.it/tB7) is a derivative of MicroPython(https://adafru.it/BeZ)

designed to simplify experimentation and education on low-cost microcontrollers. It makes it easier than ever to get prototyping by requiring no upfront desktop software downloads. Simply copy and edit files on the CIRCUITPY drive to iterate.

Your Metro M0 Express might already come with CircuitPython but maybe there's a new version, or you loaded your Metro M0 Express with Arduino code! In that case, see the below for how to reinstall or update CircuitPython. Otherwise you can skip this and go straight to the next page.

If you've already plugged your board into your computer, you should see a drive called CIRCUITPY. The drive will contain a few files.

If you have already plugged in your board, start by ejecting or "safely remove" the CIRCUITPY drive. This is a good practice to get into. Always eject before unplugging or resetting your board!

Set up CircuitPython Quick Start!

Follow this quick step-by-step for super-fast Python power :)

Download the latest version of

CircuitPython for this board via

CircuitPython.org

https://adafru.it/Emd

Click the link above and download the latest UF2 file.

Download and save it to your desktop (or wherever is handy).

Plug your Metro M0 into your computer using a known-good USB cable.

A lot of people end up using charge-only USB cables and it is very frustrating! So make sure you have a USB cable you know is good for data sync.

Double-click the Reset button next to the USB connector on your board, and you will see the NeoPixel RGB LED turn green. If it turns red, check the USB cable, try another USB port, etc.

If double-clicking doesn't work the first time, try again. Sometimes it can take a few tries to get the rhythm right!

You will see a new disk drive appear called METROBOOT.



Drag the adafruit_circuitpython_etc.uf2 file to METROBOOT.

The LED will flash. Then, the METROBOOT drive will disappear and a new disk drive called CIRCUITPY will appear.

That's it, you're done! :)

Further Information

For more detailed info on installing CircuitPython, check out Installing CircuitPython(h

ttps://adafru.it/Amd).

Installing the Mu Editor

Mu is a simple code editor that works with the Adafruit CircuitPython boards. It's written in Python and works on Windows, MacOS, Linux and Raspberry Pi. The serial console is built right in so you get immediate feedback from your board's serial output!

Mu is our recommended editor - please use it (unless you are an experienced coder with a favorite editor already!).

Download and Install Mu

Download Mu fromhttps://

codewith.mu(https://adafru.it/Be6).

Click theDownload link for downloads and installation instructions.

Click Start Hereto find a wealth of other information, including extensive tutorials and and how-to's.



Windows users: due to the nature of MSI installers, please remove old versions of Mu before installing the latest version.

Starting Up Mu

The first time you start Mu, you will be prompted to select your 'mode' - you can always change your mind later. For now please select CircuitPython!

The current mode is displayed in the lower right corner of the window, next to the "gear" icon. If the mode says "Microbit" or something else, click the Mode button in the upper left, and then choose "CircuitPython" in the dialog box that appears.

Mu attempts to auto-detect your board on startup, so if you do not have a CircuitPython board plugged in with a CIRCUITPY drive available, Mu will inform you where it will store any code you save until you plug in a board.

To avoid this warning, plug in a board and ensure that the CIRCUITPY drive is mounted before starting Mu.

Using Mu

You can now explore Mu! The three main sections of the window are labeled below; the button bar, the text editor, and the serial console / REPL.

Now you're ready to code! Let's keep going...

Creating and Editing Code

One of the best things about CircuitPython is how simple it is to get code up and running. This section covers how to create and edit your first CircuitPython program.

To create and edit code, all you'll need is an editor. There are many options. Adafruit strongly recommends using Mu! It's designed for CircuitPython, and it's really simple and easy to use, with a built in serial console!

If you don't or can't use Mu, there are a number of other editors that work quite well. The Recommended Editors page(https://adafru.it/Vue) has more details. Otherwise, make sure you do "Eject" or "Safe Remove" on Windows or "sync" on Linux after writing a file if you aren't using Mu. (This is not a problem on MacOS.)

Creating Code

Installing CircuitPython generates a code.py file on your CIRCUITPY drive. To begin your own program, open your editor, and load the code.py file from the CIRCUITPY drive.

If you are using Mu, click the Load button in the button bar, navigate to the CIRCUITPY drive, and choose code.py.

Copy and paste the following code into your editor:

import board import digitalio import time

led = digitalio.DigitalInOut(board.LED) led.direction = digitalio.Direction.OUTPUT

while True:

led.value = True time.sleep(0.5) led.value = False time.sleep(0.5)

The KB2040, QT Py and the Trinkeys do not have a built-in little red LED! There is an addressable RGB NeoPixel LED. The above example will NOT work on the KB2040, QT Py or the Trinkeys!

If you're using a KB2040, QT Py or a Trinkey, please download the NeoPixel blink

example(https://adafru.it/UDU).

The NeoPixel blink example uses the onboard NeoPixel, but the time code is the same. You can use the linked NeoPixel Blink example to follow along with this guide page.

It will look like this. Note that under the

while True: line, the next four lines

begin with four spaces to indent them, and they're indented exactly the same amount. All the lines before that have no spaces before the text.

Save the code.py file on your CIRCUITPY drive.

The little LED should now be blinking. Once per half-second.

Congratulations, you've just run your first CircuitPython program!

On most boards you'll find a tiny red LED.

On the ItsyBitsy nRF52840, you'll find a tiny blue LED.

On QT Py M0, QT Py RP2040, and the Trinkey series, you will find only an RGB NeoPixel LED.

Editing Code

To edit code, open thecode.pyfile on your CIRCUITPY drive into your editor.



Make the desired changes to your code. Save the file. That's it!

Your code changes are run as soon as the file is done saving.

There's one warning before you continue...

Don't click reset or unplug your board!

The CircuitPython code on your board detects when the files are changed or written and will automatically re-start your code. This makes coding very fast because you save, and it re-runs. If you unplug or reset the board before your computer finishes writing the file to your board, you can corrupt the drive. If this happens, you may lose the code you've written, so it's important to backup your code to your computer regularly.

There are a couple of ways to avoid filesystem corruption.

1. Use an editor that writes out the file completely when you save it.

Check out the Recommended Editors page(https://adafru.it/Vue) for details on different editing options.

If you are dragging a file from your host computer onto the CIRCUITPY drive, you still need to do step 2. Eject or Sync (below) to make sure the file is completely written.

2. Eject or Sync the Drive After Writing

If you are using one of our not-recommended-editors, not all is lost! You can still make it work.

On Windows, you can Eject or Safe Remove the CIRCUITPY drive. It won't actually eject, but it will force the operating system to save your file to disk. On Linux, use the sync command in a terminal to force the write to disk.

You also need to do this if you use Windows Explorer or a Linux graphical file manager to drag a file onto CIRCUITPY.

Oh No I Did Something Wrong and Now The CIRCUITPY Drive Doesn't Show Up!!!

Don't worry! Corrupting the drive isn't the end of the world (or your board!). If this happens, follow the steps found on the Troubleshooting(https://adafru.it/Den) page of every board guide to get your board up and running again.

Back to Editing Code...

Now! Let's try editing the program you added to your board. Open your code.py file into your editor. You'll make a simple change. Change the first 0.5 to 0.1 . The code should look like this:

import board import digitalio import time

led = digitalio.DigitalInOut(board.LED) led.direction = digitalio.Direction.OUTPUT

while True:

led.value = True time.sleep(0.1) led.value = False time.sleep(0.5)

Leave the rest of the code as-is. Save your file. See what happens to the LED on your board? Something changed! Do you know why?

You don't have to stop there! Let's keep going. Change the second 0.5 to 0.1 so it looks like this:

while True: led.value = True time.sleep(0.1) led.value = False time.sleep(0.1)

Now it blinks really fast! You decreased the both time that the code leaves the LED on and off!

Now try increasing both of the 0.1 to 1 . Your LED will blink much more slowly because you've increased the amount of time that the LED is turned on and off.

Well done! You're doing great! You're ready to start into new examples and edit them to see what happens! These were simple changes, but major changes are done using the same process. Make your desired change, save it, and get the results. That's really all there is to it!

Naming Your Program File

CircuitPython looks for a code file on the board to run. There are four options: code.t xt, code.py, main.txt and main.py. CircuitPython looks for those files, in that order, and then runs the first one it finds. While code.py is the recommended name for your code file, it is important to know that the other options exist. If your program doesn't seem to be updating as you work, make sure you haven't created another code file that's being read instead of the one you're working on.

Connecting to the Serial Console

One of the staples of CircuitPython (and programming in general!) is something called a "print statement". This is a line you include in your code that causes your code to output text. A print statement in CircuitPython (and Python) looks like this:

print("Hello, world!")

This line in your code.py would result in:

Hello, world!

However, these print statements need somewhere to display. That's where the serial console comes in!

The serial console receives output from your CircuitPython board sent over USB and displays it so you can see it. This is necessary when you've included a print statement in your code and you'd like to see what you printed. It is also helpful for troubleshooting errors, because your board will send errors and the serial console will display those too.

The serial console requires an editor that has a built in terminal, or a separate terminal program. A terminal is a program that gives you a text-based interface to perform various tasks.

Are you using Mu?

If so, good news! The serial consoleis built into Mu and willautodetect your board making using the serial console really really easy.

First, make sure your CircuitPython board is plugged in.

If you open Mu without a board plugged in, you may encounter the error seen here, letting you know no CircuitPython board was found and indicating where your code will be stored until you plug in a board.

If you are using Windows 7, make sure you installed the drivers(https://adafru.it/

VuB).

Once you've opened Mu with your board plugged in, look for the Serial button in the button bar and click it.

The Mu window will split in two, horizontally, and display the serial console at the bottom.

If nothing appears in the serial console, it may mean your code is done running or has no print statements in it. Click into the serial console part of Mu, and press CTRL+D to reload.

Serial Console Issues or Delays on Linux

If you're on Linux, and are seeing multi-second delays connecting to the serial console, or are seeing "AT" and other gibberish when you connect, then the modemma

nager service might be interfering. Just remove it; it doesn't have much use unless

you're still using dial-up modems.

To remove modemmanager , type the following command at a shell:

sudo apt purge modemmanager

Setting Permissions on Linux

On Linux, if you see an error box something like the one below when you press the S erial button, you need to add yourself to a user group to have permission to connect to the serial console.

On Ubuntu and Debian, add yourself to the dialout group by doing:

sudo adduser $USER dialout

After running the command above, reboot your machine to gain access to the group. On other Linux distributions, the group you need may be different. See the Advanced

Serial Console on Linux(https://adafru.it/VAO)for details on how to add yourself to

the right group.

Using Something Else?

If you're not using Mu to edit, are using or if for some reason you are not a fan of its built in serial console, you can run the serial console from a separate program.

Windows requires you to download a terminal program. Check out the Advanced

Serial Console on Windows page for more details.(https://adafru.it/AAH)

MacOS has Terminal built in, though there are other options available for download. C

heck the Advanced Serial Console on Mac page for more details.(https://adafru.it/

AAI)

Linux has a terminal program built in, though other options are available for download. Check the Advanced Serial Console on Linux page for more details.(https:

//adafru.it/VAO)

Once connected, you'll see something like the following.

Interacting with the Serial Console

Once you've successfully connected to the serial console, it's time to start using it.

The code you wrote earlier has no output to the serial console. So, you're going to edit it to create some output.

Open your code.py file into your editor, and include a print statement. You can print anything you like! Just include your phrase between the quotation marks inside the parentheses. For example:

import board import digitalio import time

led = digitalio.DigitalInOut(board.LED) led.direction = digitalio.Direction.OUTPUT

while True:

print("Hello, CircuitPython!") led.value = True time.sleep(1) led.value = False time.sleep(1)

Save your file.

Now, let's go take a look at the window with our connection to the serial console.

Excellent! Our print statement is showing up in our console! Try changing the printed text to something else.

import board import digitalio import time

led = digitalio.DigitalInOut(board.LED) led.direction = digitalio.Direction.OUTPUT

while True:

print("Hello back to you!") led.value = True time.sleep(1) led.value = False time.sleep(1)

Keep your serial console window where you can see it. Save your file. You'll see what the serial console displays when the board reboots. Then you'll see your new change!

The Traceback (most recent call last): is telling you the last thing your board was doing before you saved your file. This is normal behavior and will happen every time the board resets. This is really handy for troubleshooting. Let's introduce an error so you can see how it is used.

Delete the e at the end of True from the line led.value = True so that it says le

d.value = Tru

import board import digitalio import time

led = digitalio.DigitalInOut(board.LED) led.direction = digitalio.Direction.OUTPUT

while True:

print("Hello back to you!") led.value = Tru time.sleep(1) led.value = False time.sleep(1)

Save your file. You will notice that your red LED will stop blinking, and you may have a colored status LED blinking at you. This is because the code is no longer correct and can no longer run properly. You need to fix it!

Usually when you run into errors, it's not because you introduced them on purpose. You may have 200 lines of code, and have no idea where your error could be hiding. This is where the serial console can help. Let's take a look!

The Traceback (most recent call last): is telling you that the last thing it was able to run was line 10 in your code. The next line is your error: NameError: name

'Tru' is not defined . This error might not mean a lot to you, but combined with

knowing the issue is on line 10, it gives you a great place to start!

Go back to your code, and take a look at line 10. Obviously, you know what the problem is already. But if you didn't, you'd want to look at line 10 and see if you could figure it out. If you're still unsure, try googling the error to get some help. In this case, you know what to look for. You spelled True wrong. Fix the typo and save your file.

Nice job fixing the error! Your serial console is streaming and your red LED Is blinking again.

The serial console will display any output generated by your code. Some sensors, such as a humidity sensor or a thermistor, receive data and you can use print statements to display that information. You can also use print statements for troubleshooting, which is called "print debugging". Essentially, if your code isn't working, and you want to know where it's failing, you can put print statements in various places to see where it stops printing.

The serial console has many uses, and is an amazing tool overall for learning and programming!

The REPL

The other feature of the serial connection is the Read-Evaluate-Print-Loop, or REPL. The REPL allows you to enter individual lines of code and have them run immediately. It's really handy if you're running into trouble with a particular program and can't figure out why. It's interactive so it's great for testing new ideas.

Entering the REPL

To use the REPL, you first need to be connected to the serial console. Once that connection has been established, you'll want to press CTRL+C.

If there is code running, in this case code measuring distance, it will stop and you'll see Press any key to enter the REPL. Use CTRL-D to reload. Follow those instructions, and press any key on your keyboard.

The Traceback (most recent call last): is telling you the last thing your board was doing before you pressed Ctrl + C and interrupted it. The KeyboardInterrupt is you pressing CTRL+C. This information can be handy when troubleshooting, but for now, don't worry about it. Just note that it is expected behavior.

If your code.py file is empty or does not contain a loop, it will show an empty output and Code done running. . There is no information about what your board was doing before you interrupted it because there is no code running.

If you have no code.py on your CIRCUITPY drive, you will enter the REPL immediately after pressing CTRL+C. Again, there is no information about what your board was doing before you interrupted it because there is no code running.

Regardless, once you press a key you'll see a >>> prompt welcoming you to the REPL!

If you have trouble getting to the >>> prompt, try pressing Ctrl + C a few more times.

The first thing you get from the REPL is information about your board.

This line tells you the version of CircuitPython you're using and when it was released. Next, it gives you the type of board you're using and the type of microcontroller the board uses. Each part of this may be different for your board depending on the versions you're working with.

This is followed by the CircuitPython prompt.

Interacting with the REPL

From this prompt you can run all sorts of commands and code. The first thing you'll do is run help() . This will tell you where to start exploring the REPL. To run code in the REPL, type it in next to the REPL prompt.

Type help() next to the prompt in the REPL.

Then press enter. You should then see a message.

First part of the message is another reference to the version of CircuitPython you're using. Second, a URL for the CircuitPython related project guides. Then... wait. What's this? To list built-in modules type `help("modules")`. Remember the modules you learned about while going through creating code? That's exactly what this is talking about! This is a perfect place to start. Let's take a look!

Type help("modules") into the REPL next to the prompt, and press enter.

This is a list of all the core modules built into CircuitPython, including board . Remember, board contains all of the pins on the board that you can use in your code. From the REPL, you are able to see that list!

Type import board into the REPL and press enter. It'll go to a new prompt. It might look like nothing happened, but that's not the case! If you recall, the import statement simply tells the code to expect to do something with that module. In this case, it's telling the REPL that you plan to do something with that module.

Next, type dir(board) into the REPL and press enter.

This is a list of all of the pins on your board that are available for you to use in your code. Each board's list will differ slightly depending on the number of pins available. Do you see LED ? That's the pin you used to blink the red LED!

The REPL can also be used to run code. Be aware that any code you enter into the REPL isn't saved anywhere. If you're testing something new that you'd like to keep, make sure you have it saved somewhere on your computer as well!

Every programmer in every programming language starts with a piece of code that says, "Hello, World." You're going to say hello to something else. Type into the REPL:

print("Hello, CircuitPython!")

Then press enter.

That's all there is to running code in the REPL! Nice job!

You can write single lines of code that run stand-alone. You can also write entire programs into the REPL to test them. Remember that nothing typed into the REPL is saved.

There's a lot the REPL can do for you. It's great for testing new ideas if you want to see if a few new lines of code will work. It's fantastic for troubleshooting code by entering it one line at a time and finding out where it fails. It lets you see what modules are available and explore those modules.

Try typing more into the REPL to see what happens!

Everything typed into the REPL is ephemeral. Once you reload the REPL or return to the serial console, nothing you typed will be retained in any memory space. So be sure to save any desired code you wrote somewhere else, or you'll lose it when you leave the current REPL instance!

Returning to the Serial Console

When you're ready to leave the REPL and return to the serial console, simply press CT RL+D. This will reload your board and reenter the serial console. You will restart the program you had running before entering the REPL. In the console window, you'll see any output from the program you had running. And if your program was affecting anything visual on the board, you'll see that start up again as well.

You can return to the REPL at any time!

CircuitPython Libraries

As CircuitPython development continues and there are new releases, Adafruit will stop supporting older releases. Visit https://circuitpython.org/downloads to download the latest version of CircuitPython for your board. You must download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then visit https://circuitpython.org/libraries to download the latest Library Bundle.

Each CircuitPython program you run needs to have a lot of information to work. The reason CircuitPython is so simple to use is that most of that information is stored in other files and works in the background. These files are called libraries. Some of them are built into CircuitPython. Others are stored on your CIRCUITPY drive in a folder called lib. Part of what makes CircuitPython so great is its ability to store code separately from the firmware itself. Storing code separately from the firmware makes it easier to update both the code you write and the libraries you depend.

Your board may ship with a lib folder already, it's in the base directory of the drive. If not, simply create the folder yourself. When you first install CircuitPython, an empty lib directory will be created for you.

CircuitPython libraries work in the same way as regular Python modules so the Python

docs(https://adafru.it/rar) are an excellent reference for how it all should work. In

Python terms, you can place our library files in the lib directory because it's part of the Python path by default.

One downside of this approach of separate libraries is that they are not built in. To use them, one needs to copy them to the CIRCUITPY drive before they can be used. Fortunately, there is a library bundle.

The bundle and the library releases on GitHub also feature optimized versions of the libraries with the .mpy file extension. These files take less space on the drive and have a smaller memory footprint as they are loaded.

Due to the regular updates and space constraints, Adafruit does not ship boards with the entire bundle. Therefore, you will need to load the libraries you need when you begin working with your board. You can find example code in the guides for your board that depends on external libraries.

Either way, as you start to explore CircuitPython, you'll want to know how to get libraries on board.

The Adafruit CircuitPython Library Bundle

Adafruit provides CircuitPython libraries for much of the hardware they provide, including sensors, breakouts and more. To eliminate the need for searching for each library individually, the libraries are available together in the Adafruit CircuitPython Library Bundle. The bundle contains all the files needed to use each library.

Downloading the Adafruit CircuitPython Library Bundle

You can download the latest Adafruit CircuitPython Library Bundle release by clicking the button below. The libraries are being constantly updated and improved, so you'll always want to download the latest bundle.

Match up the bundle version with the version of CircuitPython you are running. For example, you would download the 6.x library bundle if you're running any version of CircuitPython 6, or the 7.x library bundle if you're running any version of CircuitPython 7, etc. If you mix libraries with major CircuitPython versions, you will get incompatible mpy errors due to changes in library interfaces possible during major version changes.

Click to visit circuitpython.org for the

latest Adafruit CircuitPython Library

Bundle

https://adafru.it/ENC

Download the bundle version that matches your CircuitPython firmware version. If you don't know the version, check the version info in boot_out.txt file on the CIRCUITPY drive, or the initial prompt in the CircuitPython REPL. For example, if you're running v7.0.0, download the 7.x library bundle.

There's also a py bundle which contains the uncompressed python files, you probably don't want that unless you are doing advanced work on libraries.

The CircuitPython Community Library Bundle

The CircuitPython Community Library Bundle is made up of libraries written and provided by members of the CircuitPython community. These libraries are often written when community members encountered hardware not supported in the Adafruit Bundle, or to support a personal project. The authors all chose to submit these libraries to the Community Bundle make them available to the community.

These libraries are maintained by their authors and are not supported by Adafruit. As you would with any library, if you run into problems, feel free to file an issue on the GitHub repo for the library. Bear in mind, though, that most of these libraries are supported by a single person and you should be patient about receiving a response. Remember, these folks are not paid by Adafruit, and are volunteering their personal time when possible to provide support.

Downloading the CircuitPython Community Library Bundle

You can download the latest CircuitPython Community Library Bundle release by clicking the button below. The libraries are being constantly updated and improved, so you'll always want to download the latest bundle.

Click for the latest CircuitPython

Community Library Bundle release

https://adafru.it/VCn

The link takes you to the latest release of the CircuitPython Community Library Bundle on GitHub. There are multiple versions of the bundle available. Download the

bundle version that matches your CircuitPython firmware version. If you don't know the version, check the version info in boot_out.txt file on the CIRCUITPY drive, or the initial prompt in the CircuitPython REPL. For example, if you're running v7.0.0, download the 7.x library bundle.

Understanding the Bundle

After downloading the zip, extract its contents. This is usually done by double clicking on the zip. On Mac OSX, it places the file in the same directory as the zip.

Open the bundle folder. Inside you'll find two information files, and two folders. One folder is the lib bundle, and the other folder is the examples bundle.

Now open the lib folder. When you open the folder, you'll see a large number of .mpy files, and folders.

Example Files

All example files from each library are now included in the bundles in an examples directory (as seen above), as well as an examples-only bundle. These are included for two main reasons:

Allow for quick testing of devices.

• Provide an example base of code, that is easily built upon for individualized

• purposes.

Copying Libraries to Your Board

First open the lib folder on your CIRCUITPY drive. Then, open the lib folder you extracted from the downloaded zip. Inside you'll find a number of folders and .mpy files. Find the library you'd like to use, and copy it to the lib folder on CIRCUITPY.

If the library is a directory with multiple .mpy files in it, be sure to copy the entire folder to CIRCUITPY/lib.

This also applies to example files. Open the examples folder you extracted from the downloaded zip, and copy the applicable file to your CIRCUITPY drive. Then, rename it to code.py to run it.

If a library has multiple .mpy files contained in a folder, be sure to copy the entire folder to CIRCUITPY/lib.

Understanding Which Libraries to Install

You now know how to load libraries on to your CircuitPython-compatible microcontroller board. You may now be wondering, how do you know which libraries you need to install? Unfortunately, it's not always straightforward. Fortunately, there is

an obvious place to start, and a relatively simple way to figure out the rest. First up: the best place to start.

When you look at most CircuitPython examples, you'll see they begin with one or more import statements. These typically look like the following:

import library_or_module

•

However, import statements can also sometimes look like the following:

from library_or_module import name

•

from library_or_module.subpackage import name

•

from library_or_module import name as local_name

•

They can also have more complicated formats, such as including a try / except block, etc.

The important thing to know is that an import statement will always include the name of the module or library that you're importing.

Therefore, the best place to start is by reading through the import statements.

Here is an example import list for you to work with in this section. There is no setup or other code shown here, as the purpose of this section involves only the import list.

import time import board import neopixel import adafruit_lis3dh import usb_hid from adafruit_hid.consumer_control import ConsumerControl from adafruit_hid.consumer_control_code import ConsumerControlCode

Keep in mind, not all imported items are libraries. Some of them are almost always built-in CircuitPython modules. How do you know the difference? Time to visit the REPL.

In the Interacting with the REPL section(https://adafru.it/Awz) on The REPL page(http

s://adafru.it/Awz) in this guide, the help("modules") command is discussed. This

command provides a list of all of the built-in modules available in CircuitPython for your board. So, if you connect to the serial console on your board, and enter the REPL, you can run help("modules") to see what modules are available for your board. Then, as you read through the import statements, you can, for the purposes of figuring out which libraries to load, ignore the statement that import modules.

The following is the list of modules built into CircuitPython for the Feather RP2040. Your list may look similar or be anything down to a significant subset of this list for smaller boards.

Now that you know what you're looking for, it's time to read through the import statements. The first two, time and board , are on the modules list above, so they're built-in.

The next one, neopixel , is not on the module list. That means it's your first library! So, you would head over to the bundle zip you downloaded, and search for neopixel. There is a neopixel.mpy file in the bundle zip. Copy it over to the lib folder on your CI RCUITPY drive. The following one, adafruit_lis3dh , is also not on the module list. Follow the same process for adafruit_lis3dh, where you'll find adafruit_lis3dh.mpy, and copy that over.

The fifth one is usb_hid , and it is in the modules list, so it is built in. Often all of the built-in modules come first in the import list, but sometimes they don't! Don't assume that everything after the first library is also a library, and verify each import with the modules list to be sure. Otherwise, you'll search the bundle and come up empty!

The final two imports are not as clear. Remember, when import statements are formatted like this, the first thing after the from is the library name. In this case, the library name is adafruit_hid . A search of the bundle will find an adafruit_hid folder.

When a library is a folder, you must copy the entire folder and its contentsas it is in the bundle to the lib folder on your CIRCUITPY drive. In this case, you would copy the entire adafruit_hid folder to your CIRCUITPY/lib folder.

Notice that there are two imports that begin with adafruit_hid . Sometimes you will need to import more than one thing from the same library. Regardless of how many times you import the same library, you only need to load the library by copying over the adafruit_hid folder once.

That is how you can use your example code to figure out what libraries to load on your CircuitPython-compatible board!

There are cases, however, where libraries require other libraries internally. The internally required library is called a dependency. In the event of library dependencies, the easiest way to figure out what other libraries are required is to connect to the serial console and follow along with the ImportError printed there. The following is a very simple example of an ImportError , but the concept is the same for any missing library.

Example: ImportError Due to Missing Library

If you choose to load libraries as you need them, or you're starting fresh with an existing example, you may end up with code that tries to use a library you haven't yet loaded. This section will demonstrate what happens when you try to utilise a library that you don't have loaded on your board, and cover the steps required to resolve the issue.

This demonstration will only return an error if you do not have the required library loaded into the lib folder on your CIRCUITPY drive.

Let's use a modified version of the Blink example.

import board import time import simpleio

led = simpleio.DigitalOut(board.LED)

while True: led.value = True time.sleep(0.5) led.value = False time.sleep(0.5)

Save this file. Nothing happens to your board. Let's check the serial console to see what's going on.

You have an ImportError . It says there is no module named 'simpleio' . That's the one you just included in your code!

Click the link above to download the correct bundle. Extract the lib folder from the downloaded bundle file. Scroll down to find simpleio.mpy. This is the library file you're looking for! Follow the steps above to load an individual library file.

The LED starts blinking again! Let's check the serial console.

No errors! Excellent. You've successfully resolved an ImportError !

If you run into this error in the future, follow along with the steps above and choose the library that matches the one you're missing.

Library Install on Non-Express Boards

If you have an M0 non-Express board such as Trinket M0, Gemma M0, QT Py M0, or one of the M0 Trinkeys, you'll want to follow the same steps in the example above to install libraries as you need them. Remember, you don't need to wait for an ImportE

rror if you know what library you added to your code. Open the library bundle you

downloaded, find the library you need, and drag it to the lib folder on your CIRCUITPY drive.

You can still end up running out of space on your M0 non-Express board even if you only load libraries as you need them. There are a number of steps you can use to try

to resolve this issue. You'll find suggestions on the Troubleshooting page(https://

adafru.it/Den).

Updating CircuitPython Libraries and Examples

Libraries and examples are updated from time to time, and it's important to update the files you have on your CIRCUITPY drive.

To update a single library or example, follow the same steps above. When you drag the library file to your lib folder, it will ask if you want to replace it. Say yes. That's it!

A new library bundle is released every time there's an update to a library. Updates include things like bug fixes and new features. It's important to check in every so often to see if the libraries you're using have been updated.

Frequently Asked Questions

These are some of the common questions regarding CircuitPython and CircuitPython microcontrollers.

I have to continue using CircuitPython 6.x or earlier. Where can I find compatible libraries?

We are no longer building or supporting the CircuitPython 6.x or earlier library bundles. We highly encourage you to update CircuitPython to the latest

version(https://adafru.it/Em8) and use the current version of the libraries(https://

adafru.it/ENC). However, if for some reason you cannot update, here are the last

available library bundles for older versions:

2.x bundle(https://adafru.it/FJA)

•

3.x bundle(https://adafru.it/FJB)

•

4.x bundle(https://adafru.it/QDL)

•

5.x bundle(https://adafru.it/QDJ)

•

6.x bundle(https://adafru.it/Xmf)

•

Is ESP8266 or ESP32 supported in CircuitPython? Why not?

We dropped ESP8266 support as of 4.x - For more information please read about it

here(https://adafru.it/CiG)!

We do not support ESP32 because it does not have native USB.

We do support ESP32-S2, which has native USB.

How do I connect to the Internet with CircuitPython?

If you'd like to include WiFi in your project, check out this guide(https://adafru.it/

F5X) on using AirLift with CircuitPython. For further project examples, and guides

about using AirLift with specific hardware, check out the Adafruit Learn

System(https://adafru.it/VBr).

Is there asyncio support in CircuitPython?

There is preliminary support for asyncio starting with CircuitPython 7.1.0. Read about using it in the Cooperative Multitasking in CircuitPython(https://adafru.it/

XnA) Guide.

My RGB NeoPixel/DotStar LED is blinking funny colors what does it mean?

The status LED can tell you what's going on with your CircuitPython board. Read

more here for what the colors mean!(https://adafru.it/Den)

What is a MemoryError?

Memory allocation errors happen when you're trying to store too much on the board. The CircuitPython microcontroller boards have a limited amount of memory available. You can have about 250 lines of code on the M0 Express boards. If you try to import too many libraries, a combination of large libraries, or run a program with too many lines of code, your code will fail to run and you will receive a

MemoryError in the serial console.

What do I do when I encounter a MemoryError?

Try resetting your board. Each time you reset the board, it reallocates the memory. While this is unlikely to resolve your issue, it's a simple step and is worth trying.

Make sure you are using .mpy versions of libraries. All of the CircuitPython libraries are available in the bundle in a .mpy format which takes up less memory than .py format. Be sure that you're using the latest library bundle(https://adafru.it/uap) for your version of CircuitPython.

If that does not resolve your issue, try shortening your code. Shorten comments, remove extraneous or unneeded code, or any other clean up you can do to shorten your code. If you're using a lot of functions, you could try moving those into a separate library, creating a .mpy of that library, and importing it into your code.

You can turn your entire file into a .mpy and import that into code.py. This means you will be unable to edit your code live on the board, but it can save you space.

Can the order of my import statements affect memory?

It can because the memory gets fragmented differently depending on allocation order and the size of objects. Loading .mpy files uses less memory so its recommended to do that for files you aren't editing.

How can I create my own .mpy files?

You can make your own .mpy versions of files with mpy-cross .

You can download mpy-cross for your operating system from here(https://

adafru.it/QDK). Builds are available for Windows, macOS, x64 Linux, and Raspberry

Pi Linux. Choose the latest mpy-cross whose version matches the version of CircuitPython you are using.

To make a .mpy file, run ./mpy-cross path/to/yourfile.py to create a yourfile.mpy in the same directory as the original file.

How do I check how much memory I have free?

Run the following to see the number of bytes available for use:

import gc gc.mem_free()

Does CircuitPython support interrupts?

No. CircuitPython does not currently support interrupts. We do not have an estimated time for when they will be included

Does Feather M0 support WINC1500?

No, WINC1500 will not fit into the M0 flash space.

Can AVRs such as ATmega328 or ATmega2560 run CircuitPython?

No.

Commonly Used Acronyms

CP or CPy = CircuitPython(https://adafru.it/KJD) CPC = Circuit Playground Classic(https://adafru.it/ncE) CPX = Circuit Playground Express(https://adafru.it/wpF) CPB = Circuit Playground Bluefruit(https://adafru.it/Gpe)

Troubleshooting

From time to time, you will run into issues when working with CircuitPython. Here are a few things you may encounter and how to resolve them.

Always Run the Latest Version of CircuitPython and Libraries

As CircuitPython development continues and there are new releases, Adafruit will stop supporting older releases. You need to update to the latest CircuitPython.(https:

//adafru.it/Em8).

You need to download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then download the latest bundle(http

s://adafru.it/ENC).

As new versions of CircuitPython are released, Adafruit will stop providing the previous bundles as automatically created downloads on the Adafruit CircuitPython Library Bundle repo. If you must continue to use an earlier version, you can still download the appropriate version of mpy-cross from the particular release of CircuitPython on the CircuitPython repo and create your own compatible .mpy library files. However, it is best to update to the latest for both CircuitPython and the library bundle.

I have to continue using CircuitPython 5.x or earlier. Where can I find compatible libraries?

Adafruit is no longer building or supporting the CircuitPython 5.x or earlier library bundles. You are highly encourged to update CircuitPython to the latest version(http

s://adafru.it/Em8) and use the current version of the libraries(https://adafru.it/ENC).

However, if for some reason you cannot update, links to the previous bundles are available in the FAQ(https://adafru.it/FwY).

Bootloader (boardnameBOOT) Drive Not Present

You may have a different board.

Only Adafruit Express boards and the SAMD21 non-Express boards ship with the UF2

bootloader (https://adafru.it/zbX)installed. The Feather M0 Basic, Feather M0

Adalogger, and similar boards use a regular Arduino-compatible bootloader, which does not show a boardnameBOOT drive.

MakeCode

If you are running a MakeCode(https://adafru.it/zbY) program on Circuit Playground Express, press the reset button just onceto get the CPLAYBOOT drive to show up. Pressing it twice will not work.

MacOS

DriveDx and its accompanything SAT SMART Driver can interfere with seeing the BOOT drive. See this forum post(https://adafru.it/sTc) for how to fix the problem.

Windows 10

Did you install the Adafruit Windows Drivers package by mistake, or did you upgrade to Windows 10 with the driver package installed? You don't need to install this package on Windows 10 for most Adafruit boards. The old version (v1.5) can interfere with recognizing your device. Go to Settings -> Apps and uninstall all the "Adafruit" driver programs.

Windows 7 or 8.1

To use a CircuitPython-compatible board with Windows 7 or 8.1, you must install a driver. Installation instructions are available here(https://adafru.it/VuB).

It is recommended(https://adafru.it/Amd) that you upgrade to Windows 10 if possible; an upgrade is probably still free for you. Check here(https://adafru.it/Amd).

Adafruit METRO M0 Express User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual