/**
@defgroup    boards_bluepill Bluepill board
@ingroup     boards
@brief       Support for the stm32f103c8 based bluepill board.

## Overview

The bluepill is an STM32F103 based board which can be bought for around
2€ on sides like AliExpress, eBay and others. Although the STM32F130C8
MCU nominally has 64 KB flash, most [actually have 128 KB
flash][Flashsize].


## Hardware

![bluepill](https://camo.githubusercontent.com/8df2fb54f87527bdd57fe007352d72c1f377d08f/687474703a2f2f77696b692e73746d33326475696e6f2e636f6d2f696d616765732f7468756d622f312f31392f53544d33325f426c75655f50696c6c5f746f702e6a70672f38303070782d53544d33325f426c75655f50696c6c5f746f702e6a7067)

### MCU

| MCU       | STM32F103C8            |
|:----------|:-----------------------|
| Family    | ARM Cortex-M3          |
| Vendor    | STMicroelectronics     |
| RAM       | 20 KB                  |
| Flash     | 64 KB / 128 KB         |
| Frequency | up to 72 MHz           |
| Timer     | 3x 16-Bit              |
| ADC       | 2x 12-bit, 10 channels |
| UART      | 3                      |
| SPI       | 2                      |
| I2C       | 2                      |
| CAN       | 1                      |
| Vcc       | 2.0 to 3.6 V           |
| Datasheet | [Datasheet][Datasheet] |


## Implementation Status

| ID    | Supported |
|:----- |:--------- |
| GPIO  | yes       |
| PWM   | yes       |
| UART  | yes       |
| ADC   | yes       |
| I2C   | no        |
| SPI   | yes       |
| USB   | no        |
| Timer | yes       |
| CAN   | no        |


## Flashing

To program and debug the board you need a SWD capable debugger. The
easiest way is using [OpenOCD][OpenOCD]. If you have OpenOCD installed,
you can flash the device with:

    $ make BOARD=bluepill flash

### Additional Flash

To make use of the entire 128 KB flash, compile your application with:

    $ make BOARD=bluepill CPU_MODEL=stm32f103cb

This sets the `CPU_MODEL` make variable to `stm32f103cb`, the default
value is `stm32f103c8`. These two CPU models basically only have one
major difference, the latter has 128 KB flash while the former has 64
KB.

If you want to flash a binary compiled this way you either need to
figure out how to adjust the OpenOCD configuration to make it use 128 KB
flash or use this [stlink fork][caboStlink] which has a
[patch][caboPatch] to make use of the entire 128 KB flash using:

    $ C8T6HACK=1 st-flash write /dev/sgX $pathToHexFile 0x8000000


## Connecting via Serial

The default UART port used is UART2, which uses pins A2 (TX) and A3 (RX).

## Using PWM

PWM is available at pins A8 to A11.

## Known Issues

### USB connector

The Micro-USB port is sometimes not soldered properly. Also, it is
usually equipped with an incorrect resistor. [This can be fixed multiple
ways][USB].

### Flashing abortion

Some boards have problems to flash on the first try. It may help, to press
the reset-button, start the flashing and release it while doing so.


## Where to buy

The board is sold under different names. On some sites it is called
`bluepill` or `blue pill`. On others you might find it by searching for
`stm32f103c8` or `stm32f103c8t6`.

Try [eBay][eBay] or [AliExpress][AliExpress].


## Further reading

* http://wiki.stm32duino.com/index.php?title=Blue_Pill
* http://wiki.stm32duino.com/index.php?title=Maple_Mini#Clones
* http://www.st.com/content/st_com/en/products/microcontrollers/stm32-32-bit-
arm-cortex-mcus/stm32-mainstream-mcus/stm32f1-series/stm32f103/stm32f103c8.html

[Datasheet]: http://www.st.com/content/ccc/resource/technical/document/datash
eet/33/d4/6f/1d/df/0b/4c/6d/CD00161566.pdf/files/CD00161566.pdf/jcr:content/tran
slations/en.CD00161566.pdf
[Flashsize]:
http://wiki.stm32duino.com/index.php?title=Blue_Pill#128_KB_flash_on_C8_version
[eBay]: https://www.ebay.com/sch/i.html?_nkw=stm32f103c8
[AliExpress]: https://www.aliexpress.com/wholesale?SearchText=STM32F103C8T6
[OpenOCD]: https://github.com/RIOT-OS/RIOT/wiki/OpenOCD
[USB]:
http://wiki.stm32duino.com/index.php?title=Blue_Pill#Hardware_installation
[imgTop]:
http://wiki.stm32duino.com/images/thumb/1/19/STM32_Blue_Pill_top.jpg/800px-
STM32_Blue_Pill_top.jpg
[caboStlink]: https://github.com/cabo/stlink
[caboPatch]:
https://github.com/cabo/stlink/commit/e2ff1710ca6caeb55b5b99f7bd8a29181ccf533d
 */