/**
@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]. By default RIOT uses the hardware
reset signal and connects to the chip under reset for flashing. This is
required to reliably connect to the device even when the MCU is in a low power
mode. Therefore not only SWDIO and SWCLK, but also the RST pin of your
debugger need to be connected to the board. Once the device is connected to
the debugger and OpenOCD is 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 STM32F103C8_FLASH_HACK=1 BOARD=bluepill

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. You may also set `STM32F103C8_FLASH_HACK` as environment variable.

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).
To use it, configure your UART to operate at a baudrate of 115200/8N1.

## 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 fails

Please check whether the debugger is properly connected, including the hardware
reset signal pin.

| Pin on Debugger    | Pin on Blue Pill |
|:------------------ |:---------------- |
| SWDIO              | DIO              |
| SWCLK              | DCLK             |
| NRST               | R                |
| GND                | GND              |
| VDD (3.3V) (*)     | 3.3              |
| Target VCC (**)    | 3.3              |

- (*)  Most debuggers have a 3.3V supply voltage to power the board. You can
       alternatively power the board using the TTL-Adapter or via Micro-USB.
- (**) Some debuggers monitor the voltage of the target MCU. Their target VCC
       pin needs to be connected to one of the 3.3V pins of the boards.

Most very cheap SWD debuggers (especially those imported for about 2€ from far
east) do not have a Target VCC pin; they will still work just fine. On these
cheap debuggers the pin to send the reset signal to the board is often either
not present or defunct. You can work around this by pressing the reset button
when OpenOCD wants to connect to the Blue Pill. Hit the reset button again after
flashing in order to boot the newly flashed image.

## 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
 */