dapboot

The dapboot project is an open-source USB Device Firmware Upgrade (DFU) bootloader for STM32 devices.

Currently, the only targets officially supported are the STM32F103x series.

Build instructions

The default target is a generic STM32F103 dev board with an LED on PC13, commonly referred to as a "bluepill" board.

To build other targets, you can override the TARGET variable when invoking make.

make clean
make TARGET=STLINK

Targets

For each of the above targets, there are three variants that can be added to the target name:

The high memory bootloader is a variation that doesn't require the application to be at an offset, the bootloader resides in the top 6.5kB of ROM and hides its reset and stack vectors inside unused entries of the application vector table. As an example, to compile for a Bluepill board with 128kB flash, use:

make clean
make TARGET=BLUEPILL_HIGH_128

Flash instructions

The make flash target will use openocd to upload the bootloader to an attached board. By default, the Makefile assumes you're using a CMSIS-DAP based probe, but you can override this by overriding OOCD_INTERFACE variable. For example:

make OOCD_INTERFACE=interface/stlink-v2.cfg flash

Overriding defaults

Local makefile settings can be set by creating a local.mk, which is automatically included.

Here is an example local.mk that changes the default target to the STLink/v2 and uses an unmodified STLink/v2 to flash it.

TARGET ?= STLINK
OOCD_INTERFACE ?= interface/stlink-v2.cfg

You can also use the env variable DEFS to override default configuration for a target, like:

# Disable LED on BluePill
DEFS="-DHAVE_LED=0" make TARGET=BLUEPILL

# Allow access to all Flash on MapleMini and change the app base address
DEFS="-DFLASH_SIZE_OVERRIDE=0x20000 -DAPP_BASE_ADDRESS=0x08004000" make TARGET=MAPLEMINI LDSCRIPT="/some/folder/stm32f103x8-16kb-boot.ld"

Using the bootloader

Building for the bootloader

The standard bootloader occupies the lower 8KiB of flash, so your application must offset its flash contents by 8KiB. This can be done by modifying your linker script or flags as appropriate.

The high memory bootloaders do not use the lower part of the flash, so you only need to make sure your application leaves 6.5kB of flash free.

Switching to the bootloader

The bootloader can be built to look for arbitrary patterns, but the default for the STM32F103 target looks for a magic value stored in the RTC backup registers. Writing the magic value and then resetting will run the bootloader instead of the main application.

The bootloader currently looks for 0x544F in RTC backup register 1 and 0x4F42 in RTC backup register 0 (together they spell "BOOT" in ASCII).

You can also use a button to stay in bootloader while booting. It's configured using HAVE_BUTTON define. If your button has a debounce capacitor, you can use BUTTON_SAMPLE_DELAY_CYCLES define to specify how many cycles to wait before sampling the I/O pin, by default it is approximately 20ms in a 72Mhz MCU.

On the bluepill boards, the default is using the BOOT1 input (available on jumper in the board) to enter the bootloader.

WebUSB

This bootloader implements the draft WebUSB specification, which allows web pages to access the bootloader (after presenting the user with a device picker dialog).

For a demo implementing dfu-util features in the browser, see https://devanlai.github.io/webdfu/dfu-util/

USB VID/PID

The USB VID/PID pair (1209/DB42) is allocated through the pid.codes open-source USB PID program.

Licensing

All contents of the dapboot project are licensed under terms that are compatible with the terms of the GNU Lesser General Public License version 3.

Non-libopencm3 related portions of the dapboot project are licensed under the less restrictive ISC license, except where otherwise specified in the headers of specific files.

See the LICENSE file for full details.