Running your own Zephyr binary on LiteX/VexRiscv in Renode

Zephyr is a very capable RTOS governed by a Linux Foundation subproject. It is very well supported on the RISC-V architecture, as well as in LiteX.

Building a Zephyr application

To install all the dependencies and prepare the environment for building the Zephyr application follow the official Zephyr Getting Started Guide up to point 4. On Linux you can follow the instructions from the point 5 on installing the Software Development Toolchain. The python version in the FOMU toolchain may not work; remove it from your PATH before attempting to build zephyr. For other operating systems, if you followed the instructions from the Required Software section of this tutorial, you should have a toolchain in PATH.

On macOS and Windows you also need to set some additional variables.

For macOS:

export ZEPHYR_TOOLCHAIN_VARIANT=cross-compile
export CROSS_COMPILE=riscv64-unknown-elf-

For Windows:

set CROSS_COMPILE=riscv64-unknown-elf-

To build the shell demo application for the LiteX/VexRiscv board run the following commands on Linux and macOS:

cd ~/zephyrproject/zephyr
west build -p auto -b litex_vexriscv samples/subsys/shell/shell_module/

And on Windows:

cd %HOMEPATH%\zephyrproject\zephyr
west build -p auto -b litex_vexriscv samples\subsys\shell\shell_module\

The resulting ELF file will be in build/zephyr/zephyr.elf.

Run the app in Renode

To run the app you just compiled, you basically need to replace the precomipled demo binary with the one you want, by setting the zephyr variable - see below.

Just like before, start Renode using the renode command (or ./renode if you built from sources).

You will see the Monitor, where you should type:

(monitor) $zephyr=@/path/to/zephyrproject/zephyr/build/zephyr/zephyr.elf
(monitor) start @scripts/single-node/litex_vexriscv_zephyr.resc

You should see a new window pop up for the serial port. In it, you should see the Zephyr interactive shell.

Debugging the app in Renode

In general, debugging in Renode is done with GDB just like with a physical board - you connect to a debug port and execute GDB commands as usual. For details, see the Renode debugging documentation.