AN4065
Application note
STM32F0xx in-application programming using the USART
Introduction
An important requirement for most Flash-memory-based systems is the ability to update
firmware when installed in the end product. This ability is referred to as in-application
programming (IAP). The purpose of this application note is to provide general guidelines for
creating an IAP application.
The STM32F0xx microcontroller can run user-specific firmware to perform IAP of the
microcontroller-embedded Flash memory. This feature allows the use of any type of
communication protocol for the reprogramming process. The USART is the example used in
this application note.
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Contents AN4065
Contents
1 IAP overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 IAP driver description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Running the IAP driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1 HyperTerminal configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Executing the IAP driver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 IAP driver menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Download image to the internal Flash memory . . . . . . . . . . . . . . . . . . . . . 7
3.2 Upload image from the internal Flash memory . . . . . . . . . . . . . . . . . . . . . 8
3.3 Execute the new program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4 Disable the write protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4 STM32F0xx IAP implementation summary . . . . . . . . . . . . . . . . . . . . . . 10
5 User program conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
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AN4065 IAP overview
1 IAP overview
STM32F0xx devices are implemented in the STMicroelectronics STM320518-EVAL
evaluation board.
1.1 Principle
Program the IAP driver to the Flash memory base address via the serial wire debug (SWD)
interface using the development toolchain of your choice or the factory-embedded
bootloader in the system memory area.
The IAP driver uses the USART to:
● Download a binary file from the HyperTerminal to the STM32F0xx's internal Flash
memory.
● Upload the STM32F0xx's internal Flash memory content (starting from the defined
user application address) into a binary file.
● Execute the user program.
1.2 IAP driver description
The IAP driver contains the following set of source files:
● main.c: where the USART initialization and RCC configuration are set. A main menu is
then executed from the menu.c file.
● menu.c: contains the main menu routine. The main menu gives the options of
downloading a new binary file, uploading the internal Flash memory, executing the
binary file already loaded, and disabling the write protection of the pages where the
user loads his binary file (if they are write protected).
● flash_if.c contains write, erase and disable write protection of the internal Flash
memory.
● common.c: contains functions related to read/write from/to the USART peripheral
● ymodem.c: is used to receive/send the data from/to the HyperTerminal application
using the YMODEM protocol
receive the file” error message is displayed. If the data is received successfully, it is
programmed into the internal Flash memory from the appropriate address. A
comparison between the internal RAM contents and internal Flash memory contents is
performed to check the data integrity. If there is any data discrepancy, the “Verification
failed” error message is displayed. Other error messages are also displayed, for
example, when the image file size is greater than the allowed memory space and when
the user aborts the task.
● STM32F0xx Standard Peripherals Library.
(a)
. In the data receiving process fails, the “Failed to
a. The Ymodem protocol sends data in 1024-byte blocks. An error check is performed in data blocks transmitted
to the STM32F0xx’s internal RAM to compare the transmitted and received data. Blocks unsuccessfully
received are acknowledged with an NAK (negative acknowledgement). For more details about the Ymodem
protocol, refer to existing documentation.
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IAP overview AN4065
The user can choose to either go to the user application or execute the IAP for
reprogramming purposes by pressing a push-button connected to a pin.
● Not pressing the push-button at reset switches to the user application
● Pressing the push-button at reset displays the IAP main menu
Refer to Ta bl e 1: STM32F0xx IAP implementation for more details about the STM320518EVAL board push-button used to enter IAP mode.
The IAP flowchart is shown in Figure 1.
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AN4065 IAP overview
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Figure 1. Flowchart of the IAP driver
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Running the IAP driver AN4065
2 Running the IAP driver
2.1 HyperTerminal configuration
To use the IAP, the user must have a PC running HyperTerminal or another terminal
program that supports ymodem protocol. In this document, the HyperTerminal is used.
Figure 2 shows the HyperTerminal configuration.
Figure 2. COM port properties
Note: The baud rate value of 115200 bps is used as an example.
Care must be taken when selecting the system clock frequency. To guarantee successful
communication via the USART, the system clock frequency in the end application must be
such that a baud rate equal to 115200 bps can be generated.
2.2 Executing the IAP driver
As an example in this application note, pressing the pin connected to the push-button allows
the IAP driver to run.
By pressing the push-button at reset, the user can run the IAP driver to reprogram the
STM32F0xx’s internal Flash memory. It is not mandatory to use the push-button; the user
can apply a signal to this pin with respect to its active level. Refer to
IAP implementation.
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Ta bl e 1: STM32F0xx
AN4065 IAP driver menu
3 IAP driver menu
Running the IAP driver displays the following menu in the HyperTerminal window.
Figure 3. IAP driver menu when the STM32F0xx Flash memory is not protected
3.1 Download image to the internal Flash memory
Follow steps 1 to 5 below to download a binary file via the HyperTerminal to the
STM32F0xx’s internal Flash memory.
1. Press 1 on the keyboard to select the Download Image to the STM32F0xx Internal
Flash menu.
2. Select Send File in the Transfer menu.
3. In the Filename field, type the name and the path of the binary file to be downloaded.
4. From the protocol list, select the Ymodem protocol.
5. Click on the Send button.
When these steps are executed, the IAP driver loads the binary file into the STM32F0xx’s
internal Flash memory from the defined base address and displays the binary file name and
size in the HyperTerminal window.
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IAP driver menu AN4065
3.2 Upload image from the internal Flash memory
Follow steps 1 to 5 below to upload a copy of the internal Flash memory started from the
user application address.
1. Press 2 on the keyboard to select Upload image from the STM32F0xx internal Flash
menu.
2. Select Receive File in the Transfer menu.
3. Select the directory to save the binary file.
4. From the protocol list, select the Ymodem protocol.
5. Click on the Receive button.
3.3 Execute the new program
Once the new program has been loaded, press 3 on the keyboard to select Execute the
New Program menu and execute the code.
3.4 Disable the write protection
When IAP starts, it checks the Flash memory pages where the user program is to be loaded
to see if any of them are write protected. If this is the case, the menu shown in
appears.
Figure 4
Figure 4. IAP driver menu when the STM32F0xx Flash memory is write protected
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AN4065 IAP driver menu
Prior to downloading the new program, the write protection function must be disabled. To do
so, press 4 (Disable the write protection) on the keyboard. Write protection is disabled and
a system reset is generated to reload the new option byte values. After resuming from reset,
the menu shown in
Figure 3 is displayed if the key push-button is pressed.
Note: In the current application, read protection is not supported, so the user has to verify that the
Flash memory is not read-protected.
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STM32F0xx IAP implementation summary AN4065
4 STM32F0xx IAP implementation summary
Ta bl e 1 provides a summary of the STM320518-EVAL IAP implementation.
Table 1. STM32F0xx IAP implementation
Firmware Hardware
IAP program is
located at
0x8000000. Flash
routines
(program/erase)
are executed from
the Flash memory.
Size of IAP
program program
is about 6 Kbytes.
User application
(image to be
downloaded with the
IAP) is programmed
starting from address
0x8003000
(1)
Image is uploaded
with IAP from
STM32F0xx internal
Flash
Push-button
(active level:
high)
USART
used
STM32F0xx devices
(STM320518-EVAL)
1. The user application location address is defined in the flash_if.h file as: #define APPLICATION_ADDRESS
0x8003000.To modify it, change the default value to the desired one.
Sector 0 - Sector 1
52 Kbytes
(Sector 3 - Sector 15)
52 Kbytes
(Sector 3 - Sector 15)
Push-button
connected to
pin PB8
The STM32F0xx IAP package comes with:
● Source files and preconfigured projects for the IAP program (see:
Project\STM32F0xx_IAP directory)
● Source files and preconfigured projects that build the application to be loaded into
Flash memory using the IAP (see: Project\STM32F0xx_IAP\binary_template
directory).
The readme.txt files provided within this package describe, in a step by step fashion, how to
execute the current IAP application.
USART1
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AN4065 User program conditions
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5 User program conditions
The user application to be loaded into the Flash memory using IAP should be built with the
following configuration settings:
1. Set the program load address at 0x08003000, using the toolchain linker file.
2. Relocate the vector table at address 0x20000000 (reserve 48 word starting in RAM @
0x20000000 ).
An example application program to be loaded with the IAP application is provided with
preconfigured projects.
Figure 5. Flash memory usage
1. The top Flash memory address is 0x0800 7FFF for STM32F0xx devices
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Revision history AN4065
6 Revision history
Table 2. Document revision history
Date Revision Changes
03-May-2012 1 Initial release.
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AN4065
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