/**
@defgroup    boards_arduino-zero Arduino Zero
@ingroup     boards
@brief       Support for the Arduino Zero board.

## Overview

The `Arduino Zero` is a board by Arduino/Genuino featuring a ATSAMD21G18A.
The SAMD21 is a ARM Cortex-M0+ micro-controller.  It has 256KiB of flash memory
and 32KiB of RAM.

This board is available [here](https://store.arduino.cc/product/GBX00003).

## Hardware

![arduino-zero](https://www.arduino.cc/en/uploads/Main/ABX0003_iso_both.jpg)


### MCU
| MCU           | ATSAMD21G18A                          |
|:------------- |:------------------------------------- |
| Family        | ARM Cortex-M0+                        |
| Vendor        | Atmel                                 |
| RAM           | 32KiB                                 |
| Flash         | 256KiB                                |
| Frequency     | up to 48MHz                           |
| FPU           | no                                    |
| Timers        | 6 (1x 16-bit, 2x 24-bit, 3x 32-bit)   |
| ADCs          | 6x 12-bit channels)                   |
| UARTs         | 2                                     |
| SPIs          | max 6 (see UART)                      |
| I2Cs          | max 6 (see UART)                      |
| Vcc           | 1.8V - 3.6V                           |
| Datasheet     | [Datasheet](http://ww1.microchip.com/downloads/en/DeviceDoc/SAM_D21_DA1_Family_Data%20Sheet_DS40001882E.pdf) |

### User Interface

1 LED:

| Device | PIN  |
|:------ |:---- |
| LED0   | PA17 |


## Implementation Status

Notice that the initial support for the Arduino Zero was based on samr21-xpro
and Sodaq Autonomo.

| Device | ID        | Supported | Comments  |
|:------------- |:------------- |:------------- |:------------- |
| MCU        | samd21    | partly    | Energy saving modes not fully utilized |
| Low-level driver | GPIO    | yes       | |
|        | PWM       | to be tested      | |
|        | UART      | yes           | two UARTs|
|        | I2C       | yes       | |
|        | SPI       | yes       | |
|               | ADC           | not implemented           | |
|        | USB       | no        | |
|        | RTT       | yes       | |
|        | RTC       | yes       |  |
|        | RNG       | no        | no HW module |
|        | Timer     | yes           | |


Detailed information on the board can be found on [the official web page](https://www.arduino.cc/en/Main/ArduinoBoardZero).

## Flashing the device

The standard method for flashing RIOT to the Arduino Zero is using OpenOCD.
For this to work properly, **you have to make sure to use a very recent version
of OpenOCD**.  Arduino-IDE comes with openocd v0.9.0  which is known to work.
Also Ubuntu 16.04 has openocd v0.9.0.

Refer to https://github.com/RIOT-OS/RIOT/wiki/OpenOCD for building OpenOCD
and make sure "cmsis-dap" and "hidapi-libusb" are enabled.

## Supported Toolchains

To build software for the Arduino Zero board we strongly recommend the usage
of the [GNU Tools for ARM Embedded Processors](https://launchpad.net/gcc-arm-embedded) toolchain.


## Known Issues / Problems

### Stack sizes
The default stack sizes have not been tuned properly yet. If in doubt why
your application crashes try increasing the default stack sizes and use `ps` to
find out how much stack is being used.
Tracked in https://github.com/RIOT-OS/RIOT/issues/2228
 */