STM32 Bluepill Dev Notes

STM32

ARM Cortex M3 dev board, many cheap clones on Aliexpress (~ 120INR), well supported, fast, low power consumption

Figure 1. Pinout

Chip comes with a system BL in read only ROM/silicon that allows flashing over serial port and then jumps to 0x8000000. You could have a custom boot loader there that does additional stuff. There’s a few community developed ones

Serial - in built as above, cannot be removed.

Pins
- PA9 - TX
- PA10 - RX
BOOT0 should be high
Needs a USB to UART converter

STM32Duino/ Roger’s BL/ Maple BL 2.0

Stable, works well for me.
Has a fastboot version that works without waiting.
Once flashed, disable SWD pins so flashing over STlink won’t work anymore
- FIX: Keep BOOT1 high/floating during reset so that it goes into permanent DFU mode and can be detected over STlink
has a 5 sec wait during boot where it waits for DFU (Device Firmware Update) upload. Use the FASTBOOT version

Flashing

STM32_Programmer.sh -c port=SWD -e all -d /data/common/stm32/BL/generic_boot20_pc13.bin  0x8000000 -v

Maple 2.0 - FASTBOOT

Avoids 5s wait if waking up from STANDBY/SLEEP (unless BOOT1 is high)

Flash with STM32_programmer

# flash normal bl first.
STM32_Programmer.sh -c port=SWD -e all -d /data/common/stm32/BL/generic_boot20_pc13.bin  0x8000000 -v
# then flash fastboot
STM32_Programmer.sh -c port=SWD  -d /data/common/stm32/BL/generic_boot20_pc13_fastboot.bin  0x8000000

USB HID

new one - worked a few times and then ran into trouble with it. Try again later.

Does BL matter?

It should not - apart from the convenience of flashing and then jumping to your user code. But, it does - my code to check wake up reason and go into standby/sleep didn’t work without maple BL. See STM32Sleep - Hang if flashed via SWD, works if using STM32Duino bootloader

Cores

Cores refers to platform/foundation libs that are used to bring the board up and then expose a Arduino API on top. THere are multiple cores

Roger’s Core/Maple Core - More stable, things generally work, has libs and you get better forum support for blue pill. However, with official STM core coming in, this is unlikely to be developed further. For blue pill, stay on this.
Official STM32 Arduino Core - newer, official, under development. Things sometime work and while improving, sometimes things may not do what it says on the tin. However, keep this under watch. Apparently has better support STM32F4.

Problems

USB enumeration fails - esp when using Official STM Core

Workaround: initialize Serial1 (PA9, PA10) and write msgs to it.

#include "src/LibC/LibC.h"

void setup(void)
{
     Serial1.begin(9600);
     printf_setprint(&Serial1);
     // this will appear on Pa9, PA10
     printf("\r\nWUF : %lu", PWR->CSR && PWR_CSR_WUF);
     // ....
}

You’ll need the USB-UART adapter to connect and read from PA9/PA10 of course.

RF24 lib didn’t seem to like the official STM core much
- configuration wasn’t sticking and it was showing weird values
Could not read WUF/SBF with Official STM core

References

Data sheet

STM32

Bootloader