# Bare Metal Demo App

This directory provides a minimal bare metal demo app that demonstrates how to easily create a bare metal C application and load it/run it on the CPU of a SoC.

## Build and Load over LiteX-Term

To build a LiteX SoC for the Arty board (available in LiteX-Boards) and build the demo app for it, execute the following commands:

```bash
python3 -m litex_boards.targets.digilent_arty --build --load
litex_bare_metal_demo --build-path=build/digilent_arty
```

Where `--build-path` is the build path to the Arty build directory. The Arty board is used here but almost any another board supported in LiteX-Boards could be used. When no external RAM is provided directly by the board, `--integrated-main-ram-size` argument could be used to add some integrated RAM in the SoC and be able to execute the demo from it. (ex `--integrated-main-ram-size=0x8000` will add 32KB of integrated RAM).

Loading the compiled demo app can be done in different ways as explain in LiteX's [wiki](https://github.com/enjoy-digital/litex/wiki/Load-Application-Code-To-CPU)

Since our app is small and for simplicity we'll just load it over serial here: `$ litex_term /dev/ttyUSBX --kernel=demo.bin`

You should see the minimal demo app running and should be able to interact with it:

```shell
--============== Boot ==================--
Booting from serial...
Press Q or ESC to abort boot completely.
sL5DdSMmkekro
[LITEX-TERM] Received firmware download request from the device.
[LITEX-TERM] Uploading demo.bin to 0x40000000 (9264 bytes)...
[LITEX-TERM] Upload complete (9.8KB/s).
[LITEX-TERM] Booting the device.
[LITEX-TERM] Done.
Executing booted program at 0x40000000

--============= Liftoff! ===============--

LiteX minimal demo app built Dec 10 2020 17:13:02

Available commands:
help               - Show this command
reboot             - Reboot CPU
led                - Led demo
donut              - Spinning Donut demo
litex-demo-app> led
Led demo...
Counter mode...
Shift mode...
Dance mode...
litex-demo-app> donut
Donut demo...

                                      $$$$$@@@@@
                                  $##########$$$$$$$$
                                ###*!!!!!!!!!***##$$$$$$
                              ***!!====;;;;===!!**###$$$$#
                            **!===;;;:::::;:===!!**####$##
                          !*!!==;;:~-,,.,-~::;;=!!**#######!
                          !!!!=;:~-,.......-~::==!!***#####*
                          !!!!==;~~-.........,-:;==!!***###**!
                          !**!!=;:~-...     ..-:;=!!!********!
                        ;!*#####*!!;.       ~:;==!!!******!!=
                        :!*###$$$$#*!      :;==!!!!!****!!!=;
                        ~=!*#$$$@@@$$##!!!!!!!!!!!!****!!!!=;
                          ;=!*#$$$@@@@$$#*******!*!!*!!!!!==;~
                          -;!*###$$$$$$$###******!!!!!!!===;~
                          -;!!*####$#####******!!!!!!==;;:-
                            ,:=!!!!**#**#***!!!!!!!====;:~,
                              -:==!!!*!!*!!!!!!!===;;;:~-
                                .~:;;========;=;;:::~-,
                                  .--~~::::~:~~--,.
litex-demo-app>
```

## Replace the LiteX BIOS with the Demo App

In some cases, we'll just want to replace the LiteX BIOS with our custom app. This demo can be used as a basis to create a such custom app.

The demo will be recompiled to target the ROM of the SoC:

```bash
litex_bare_metal_demo --build-path=build/arty/ --mem=rom
```

The SoC can then be re-compiled to integrate the demo app in the ROM with:

```bash
python3 -m litex_boards.targets.digilent_arty --integrated-rom-init=demo.bin --build --load
```

When loading the bitstream, you should then directly see the demo app executed:

```shell
LiteX minimal demo app built Dec 10 2020 17:13:02

Available commands:
help               - Show this command
reboot             - Reboot CPU
led                - Led demo
donut              - Spinning Donut demo
litex-demo-app>
```

## Going further

To create more complex apps, feel free to explore the source code of the BIOS or other open source projects build with LiteX on the [GitHub wiki](https://github.com/enjoy-digital/litex/wiki/Projects).