/**
@defgroup    boards_nrf52840dongle nRF52840-Dongle
@ingroup     boards
@brief       Support for the nRF52840-Dongle

### General information

The nRF52840-Dongle is a bare USB-stick shaped device that houses barely
anything than the nRF52840 itself, which offers BLE and 802.15.4 and USB
connectivity.

Unlike similar sticks (like the @ref boards_nrf52840-mdk), it features no
dedicated programmer hardware but relies on direct USB communication with a
built-in bootloader.

The board features two LEDs (LD1: green, LD2: RGB), a user (SW1) and a
reset button as well as 15 configurable external pins.

### Links

- [nRF52840 web page](https://www.nordicsemi.com/?sc_itemid=%7BCDCCA013-FE4C-4655-B20C-1557AB6568C9%7D)
- [documentation and hardware description](https://infocenter.nordicsemi.com/topic/ug_nrf52840_dongle/UG/nrf52840_Dongle/intro.html?cp=3_0_5)

### Flash the board

The board is flashed using its on-board boot loader; the
[nrfutil](https://github.com/NordicSemiconductor/pc-nrfutil) program needs to
be installed. That can turn the binary into a suitable zip file and send it to the
bootloader.

The process is automated in the usual `make flash` target. For that process to
complete, you need to enter the bootloader manually by pressing the board's
reset button. Readiness of the bootloader is indicated by LD2 pulsing in red.

#### nrfutil installation

On systems with Python 2 available, `pip install nrfutil` works.

On systems with Python 3, a recent version of pip is required to install all dependencies;
you may need to run `pip install --upgrade pip` before being able to run `pip install nrfutil` successfully.

### Accessing STDIO

The usual way to obtain a console on this board is using an emulated USB serial port (CDC-ACM).
This is available automatically using the `stdio_cdc_acm` module,
unless any other stdio module is enabled.

On Linux systems with ModemManager < 1.10 installed,
`make term` will, in some setups, fail for a few seconds after the device has come up.
This is [fixed in its 1.12.4 version](https://gitlab.freedesktop.org/mobile-broadband/ModemManager/issues/164),
but should not be more than a short annoyance in earlier versions.

To ease debugging,
pins 0.13 and 0.15 are configured as RX and TX, respectively.
They provide stdio if no CDC-ACM is disabled,
and can be used as a custom UART otherwise.

 */