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Unfortunately, the crippled versions of “Bluepill” boards with STM32F103C6xx chips instead of STM32F103C8xx are now sold all over the place, sometimes advertised in a confusing way to make the difference not noticeable until too late. Add minimal support for these MCUs in the common “Bluepill with stm32duino” configuration, so that it could be possible to make something useful from those boards (although fitting QMK into the available 24 KiB of flash may be rather hard). (In fact, I'm not sure whether the “STM32” part of the chip name is actually correct for those boards of uncertain origin, so the onekey board name is `bluepill_f103c6`; another reason for that name is to match the existing `blackpill_f401` and `blackpill_f411`.) The EEPROM emulation support is not included on purpose, because enabling it without having a working firmware size check would be irresponsible with such flash size (the chance that someone would build a firmware where the EEPROM backing store ends up overlapping some firmware code is really high). Other than that, enabling the EEPROM emulation code is mostly trivial (the `wear_leveling` driver with the `embedded_flash` backing store even works without any custom configuration, although its code is significantly larger than the `vendor` driver, which may also be important for such flash size).
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STM32F103C6xx Bluepill onekey
- Supported hardware: Bluepill boards with the STM32F103C6xx chips
Note that STM32F103C6xx chips have only 32 KiB of flash and 10 KiB of RAM, and the stm32duino bootloader occupies 8 KiB of flash, leaving only 24 KiB for the firmware, therefore the capabilities of this board are severely restricted in comparison to proper Bluepill boards with STM32F103CBxx or STM32F103C8xx chips (128 or 64 KiB of flash and 20 KiB of RAM). You may need to disable many features in the QMK firmware to bring its compiled size below 24 KiB. Please avoid designing new keyboards with these MCUs unless you are stuck with some hardware that you already have and don't want to just throw away.
To trigger keypress, short together pins B0 and A7.