/**
@defgroup    boards_feather-m0 Adafruit Feather M0
@ingroup     boards
@brief       Support for the Adafruit Feather M0.

### General information

Feather M0 boards are development boards shipped by
[Adafruit](https://learn.adafruit.com/adafruit-feather-m0-basic-proto/).

All the feather M0 boards are built based on the same Atmel SAMD21G18A
microcontroller. See @ref cpu_samd21.

Several types of Feather M0 boards exist:
* [Feather M0 WiFi](https://learn.adafruit.com/adafruit-feather-m0-wifi-atwinc1500/)
* [Feather M0 BLE](https://learn.adafruit.com/adafruit-feather-m0-bluefruit-le/overview)
* [Feather M0 Adalogger](https://learn.adafruit.com/adafruit-feather-m0-adalogger/)
* [Feather M0 LoRa](https://learn.adafruit.com/adafruit-feather-m0-radio-with-lora-radio-module)

The different modules used to differenciate the boards (ATWINC1500 WiFi,
Bluefruit LE, SD card, LoRa) are connected via SPI (SPI_DEV(0)) to the
SAMD21 mcu.

### Pinout

<img src="https://cdn-learn.adafruit.com/assets/assets/000/030/921/original/adafruit_products_2772_pinout_v1_0.png"
     alt="Adafruit Feather M0 proto pinout" style="width:800px;"/><br/>

`AIN7` can be used to [measure the voltage of a connected Lipoly battery][battery].
It is mapped to ADC_LINE(6) in RIOT.

~~~~~~~~~~~~~~~~ {.c}
int vbat = adc_sample(ADC_LINE(6), ADC_RES_10BIT);
vbat *= 2;      /* voltage was divided by 2, so multiply it back */
vbat *= 33;     /* reference voltage 3.3V * 10 */
vbat /= 10240;  /* resolution * 10 (because we multiplied 3.3V by 10) */
printf("Bat: %dV\n", vbat);
~~~~~~~~~~~~~~~~

[battery]: https://learn.adafruit.com/adafruit-feather-m0-basic-proto/power-management#measuring-battery-4-9

### Flash the board

1. Put the board in bootloader mode by double tapping the reset button.<br/>
   When the board is in bootloader mode, the user led (red) oscillates smoothly.


2. Use `BOARD=feather-m0` with the `make` command.<br/>
   Example with `hello-world` application:
```
     make BOARD=feather-m0 -C examples/hello-world flash
```

### Accessing STDIO via UART

To access the STDIO of RIOT, a FTDI to USB converted needs to be plugged to
the RX/TX pins on the board.
 */