CS32 Blue Pill clone connection problems

Recently I’ve been doing some experiments with the popular “Blue Pill” microcontroller model STM32F103C8T6, made by STMicroelectronics. The microcontroller (MCU) uses the ARM Cortex-M3 F103 chip, a low cost, low power but high capability chip, with a whole load of input/output pins.

Instead of using the original, I stupidly decided to get a much cheaper Chinese clone, with model number CS32F103C8T6 – note the difference in the first two letters. I ran into some weird connection issues, which did not appear with an original MCU.

After a few days of tearing my hair out, I managed to resolve them. I’m leaving some notes here on the interwebs just in case someone else has the same problems.

ST-LINK V2 hardware programmer

This is needed to connect to your MCU. Make sure to connect the correct pins, otherwise your MCU will just silently get bricked. I bricked one of the clone MCUs this way, and never knew until I gave up trying to connect after nothing worked.

Texane/Stlink open source tool

Texane/Stlink is an open source version of the STMicroelectronics STLink tools, used to program the MCU. I prefer this as it is more cross-platform and also runs on Mac and Linux, compared to the proprietary STMicroelectronics one which only runs on Windows.

After connecting the computer to the MCU, through the ST-Link v2 hardware programmer, running the st-info --probe command gives an “unknown device” error. Other Stlink commands don’t work.

$ st-info --probe
Found 1 stlink programmers
 serial: 563f6f06513f52481953253f
openocd: "\x56\x3f\x6f\x06\x51\x3f\x52\x48\x19\x53\x25\x3f"
  flash: 0 (pagesize: 0)
   sram: 0
 chipid: 0x0000
  descr: unknown device

The trick is to play around with the reset button on the MCU.

Do this:

• Unplug the MCU from the programmer, or unplug the programmer from your computer’s USB port
• Plug it back in
• Before issuing another Stlink command, press and hold the reset button on the MCU
• While holding the Reset button, issue the command st-info --probe
• Connection succeeds and MCU info is shown – see below

$ st-info --probe
Found 1 stlink programmers
 serial: 563f6f06513f52481953253f
openocd: "\x56\x3f\x6f\x06\x51\x3f\x52\x48\x19\x53\x25\x3f"
  flash: 131072 (pagesize: 1024)
   sram: 20480
 chipid: 0x0410
  descr: F1 Medium-density device

Subsequent Stlink commands should work. If this issue re-appears, following the procedure above should resolve it.

ST-Link Utility on Windows

Using STMicroelectronics’s proprietary ST-Link Utility on Windows will also give you similar issues.

Again, this is resolved by playing around with the reset button:

• Press and hold the reset button on the MCU
• In the ST-Link Windows application, go to Menu: Target -> Connect

• The app window will appear to freeze
  Release the reset button
  The app will now show data read from the MCU

Further thoughts

In both use cases above, use of the reset button needed to be combined with an unplug/re-plug process.

Maybe it has to do with the reset action needing to be accompanied by a power cycle?