Controlling the STM32 bootloader mode

The STM32 microcontroller has a built-in bootloader that is capable of updating the user flash over USART1. See AN2606 for details.

On the Chameleon v3, the signals needed to enter and exit bootloader mode can be controlled over a USB connection. This document describes a utility that resets the STM32 into bootloader or user flash mode.

Programming the FT232R CBUS pins

On the Chameleon v3, the BOOT[1:0] and RST_L signals are connected to the CBUS[2:0] pins on the FT232R. These pins must be programmed as GPIO; see Chameleon V3 Proto0 Care and Feeding document.

Building stm32reset

stm32reset uses libgpiod to access the FT232R CBUS pins as GPIO pins from user space.

Install gpiod and the development libraries.

$ sudo apt-get install gpiod libgpiod-dev

Use gpiodetect to verify that the libraries correctly detect the FT232R.

$ sudo gpiodetect
gpiochip0 [ftdi-cbus] (4 lines)
$ sudo gpioinfo 0
gpiochip0 - 4 lines:
    line   0:      unnamed       unused   input  active-high
    line   1:      unnamed       unused   input  active-high
    line   2:      unnamed       unused   input  active-high
    line   3:      unnamed       unused   input  active-high

Build stm32reset:

~/chromiumos/src/platform/chameleon/utils/stm32reset$ make
gcc -Wall -Wextra -g -std=gnu89 -o stm32reset stm32reset.c -l gpiod

Resetting into bootloader mode

To reset the STM32 into bootloader mode, run stm32reset --bootloader. The STM32 will remain in bootloader mode until it is reset (or power cycled).

$ sudo ./stm32reset --bootloader
$ stm32flash /dev/ttyUSB0
stm32flash 0.5

http://stm32flash.sourceforge.net/

Interface serial_posix: 57600 8E1
Version      : 0x30
Option 1     : 0x00
Option 2     : 0x00
Device ID    : 0x0430 (STM32F10xxx XL-density)
- RAM        : 96KiB  (2048b reserved by bootloader)
- Flash      : 1024KiB (size first sector: 2x2048)
- Option RAM : 16b
- System RAM : 6KiB

Resetting into user flash mode

stm32flash expects to communicate with the flash bootloader. When the program in user flash is running, stm32flash will report a failure to initialize.

$ sudo ./stm32reset --user
$ stm32flash /dev/ttyUSB0
stm32flash 0.5

http://stm32flash.sourceforge.net/

Interface serial_posix: 57600 8E1
Failed to init device.

Multiple FT232R devices

If you have more than one FT232R plugged into your computer, determine which device is the Chameleon v3. It should have entries in /dev for ttyUSBn and gpiochipn. The n is the device number to pass to stm32reset with the -d or --device option.