Adafruit SAMD User Manual

How to Program SAMD Bootloaders

Created by Brent Rubell

Last updated on 2020-10-22 05:04:48 PM EDT

Overview

Do you have a bricked Adafruit SAMD board that won't boot into CircuitPython, or show up as a boot volume? Are you building your own SAMD board and want to flash our UF2-SAMD bootloader onto it?

This guide will cover wiring a J-Link to a SAMD board, flashing the bootloader, and (optionally) installing the latest

CircuitPython build.

This process does require extra hardware and some software installation time. It is unfortunate when a

microcontroller's firmware is corrupted - it does not happen often. But, rather than buy a new board and have one

sitting, this process will get your original board back to 100%.

About the SAMD UF2 Bootloader

You will need to program the Adafruit UF2-SAMD Bootloader (https://adafru.it/Dj0) onto the affected board. 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

If you have a functioning bootloader on your board, you do not need to use the techniques described in this

Guide to update the bootloader. Instead, refer to the Guide for your board about how to update.

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UF2 file onto a removable drive

.

Parts

To flash the bootloader, you'll need a JTAG/SWD debugger. We suggest the J-Link EDU Mini. This version is smaller (the size of a USB drive) and less expensive than the full-sized J-Link EDU, BUT it is for non-commerical use only.

What does that mean?

Basically, if you're making money (or plan to make money) off your project, you'll need to order the full commercial

version, or find a different debugger that suits your needs and budget better. But if you're working on personal, non-

commercial projects, such as publishing some open source designs you're not selling yourself, you're good. You don't

need to be a student, and you can even be a paid engineer during the week, using this on the weekend for personal

non-commercial projects. As long are your intentions are non-commercial, the J-Link EDU is an excellent choice!

We also carry the full-sized J-Link EDU (https://adafru.it/e9G)and the J-Link base (https://adafru.it/e5q) (this model is for

commercial use).

If you're a commercial user (not educational/home hobby) - you must use the commercial J-Link Base

The process for using the J-LINK models is identical, only differing in the software you will install for the specific unit on

the next page.

You'll also want to get a JTAG to SWD converter board and SWD cable (not needed for the JLink mini), and a SWD

breadboard breakout

SEGGER J-Link EDU Mini - JTAG/SWD Debugger

$19.95

IN STOCK

Add To Cart

SEGGER J-Link BASE - JTAG/SWD Debugger

$399.95

IN STOCK

Add To Cart

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

$4.95

IN STOCK

Add To Cart

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

$2.95

IN STOCK

Add To Cart

SWD (2x5 1.27mm) Cable Breakout Board

$1.95

IN STOCK

Add To Cart

Setup

Installing J-Link

Navigate to the Seger downloads page (https://adafru.it/vaI) and install the version of the

J-Link Software and

Documentation Pack

for your operating system:

Grab a Bootloader

You'll also want to download a compiled bootloader binary (.bin file) for the board you're recovering. These can be

found on the Adafruit/uf2-samdx1 repository (https://adafru.it/D3C):

https://adafru.it/D3C

(Optional) Grab the Latest CircuitPython UF2

If you want to install CircuitPython onto the UF2 bootloader, you'll need a board-specific .uf2 file. Click here to find the

latest build:

https://adafru.it/tBa

Click the file corresponding to the CircuitPython board you're recovering. Check the two letter code for your language: english, espagnol, french, filipino (tagalog) - we'll be using the english build but instructions are the same for

other languages.

When the UF2 finishes downloading, move the file to your Desktop.

We'll leave this file alone and come back to it when we're ready to load CircuitPython onto our board's boot drive.

Metro M0/M4 Wiring

The Adafruit Metro M0 and M4 have a socket for connecting to a SWD cable built-in - you can connect (and

disconnect) a SWD cable quickly.

Remove the small plastic cap cap from the SWD socket

on the Metro.

Then, connect the SWD cable from the J-Link to the

Metro.

Once the Metro is wired up, plug the J-Link into a USB

port on your computer and wait for the status indicator

LED to turn green.

Then, plug a USB cable into the Metro, this is required!

ItsyBitsy M0/M4 Wiring

The ItsyBitsy has pins SWDIO and SWCLK broken out on the back edge of the board. You'll need a SWD cable

breakout to connect the J-Link to an ItsyBitsy:

ItsyBitsy Wiring

Make the following connections between the ItsyBitsy M0/M4 and the SWD Cable Breakout:

ItsyBitsy GND to Breakout GND ItsyBitsy 3V to Breakout VRef ItsyBitsy SWCLK to Breakout CLK ItsyBitsy SWDIO to Breakout SWIO

SWD (2x5 1.27mm) Cable Breakout Board

$1.95

IN STOCK

Add To Cart

You must also plug in a USB cable to the ItsyBitsy to power it during progamming

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Adafruit SAMD User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual