docs/platforms/risc-v/litex/boards/arty_a7: Migrate README.txt

Migrated legacy README.txt documentation to RST format which aligns with
the standard template for board documentation.

Signed-off-by: Matteo Golin <matteo.golin@gmail.com>

Documentation/platforms/risc-v/litex/boards/arty_a7/index.rst

@@ -1,6 +1,102 @@
 =======
-arty_a7
+Arty A7
 =======
 
-.. include:: README.txt
+.. tags:: arch:riscv, vendor:sifive, experimental
-   :literal:
+
+.. todo::
+
+      There is currently no support for GPIO, SPI, I2C, RTC, WDT or PWM. There
+      is also no support for RISC-V user mode yet. If you are interested in
+      contributing one of these features, please see :doc:`/contributing/index`.
+
+.. figure:: arty_a7.jpg
+   :figwidth: 50%
+   :align: center
+   :alt: The Arty A7 development board
+
+   The Arty A7 development board
+
+The Arty A7 is an Artix 7 FPGA development board. There is some external
+documentation about the board itself (and its datasheets) `here
+<https://digilent.com/reference/programmable-logic/arty-a7/start>`_.
+
+Features
+========
+
+* 450MHz internal clock
+* 16MB QSPI flash
+* 10/100Mbps Ethernet
+* 256MB DDR3 @333MHz
+* JTAG programmable
+* 5200 logic slices
+* 1800Kbits of block RAM
+
+Buttons and LEDs
+================
+
+The board has:
+
+* 4 switches
+* 4 buttons
+* 1 RESET LED
+* 1 User LED
+* 4 User RGB LEDs
+
+Power Supply
+============
+
+The board can be supplied power over USB, or a 7-15V 2.5mm coaxial supply. The
+logic level of the A7 is 3V3.
+
+Installation
+============
+
+You will need to download the tool-chain for this board:
+
+.. code:: console
+
+   $ curl https://static.dev.sifive.com/dev-tools/riscv64-unknown-elf-gcc-8.3.0-2019.08.0-x86_64-linux-ubuntu14.tar.gz
+
+Flashing
+========
+
+1. Follow the instructions on https://github.com/enjoy-digital/litex to build
+   the vexriscv softcore fpga gateware and flash to Arty A7 board:
+
+.. code:: console
+
+   $ cd litex-boards/litex_boards/targets
+   $ ./digilent_arty.py --with-ethernet --with-sdcard --uart-baudrate 1000000 --cpu-type=vexriscv --cpu-variant=secure --build --load --flash
+
+
+2. Next, set up a TFTP server on your host machine, copy ``nuttx.bin`` to your
+   ``tftpboot`` directory and change its name to ``boot.bin``.
+
+3. Setup the wired connection (UART and TFTP) between your A7 board and host
+   machine.
+
+4. Run the following command:
+
+   .. code:: console
+
+      $ minicom -b 1000000 /dev/ttyUSB1 # The default baudrate on litex vexriscv is 1e6
+
+   When you see the bios prompt ``litex>``, type ``netboot`` and press "Enter".
+   You should then see the NSH prompt.
+
+Configurations
+==============
+
+You can configure NuttX for this board using:
+
+.. code:: console
+
+   $ ./tools/configure.sh arty_a7:<config>
+
+Where ``<config>`` is the name of one of the configurations listed below.
+
+nsh
+---
+
+A simple configuration with the NSH shell.