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The RISC-V GNU Toolchain, FreeRTOS and QEMU

About

Emulation eases the software development process when the target architecture is different than the host machine. This document explains how to setup a development Toolchain and use the Quick Emulator (QEMU) to run a FreeRTOS "demo" targeted to the RISCV-V architecture.

The explanation goes for two different operating systems, Gentoo GNU/Linux and OpenBSD.

Setup in Gentoo

Install the RISC-V GNU Toolchain

crossdev enables a Gentoo system to provide cross-compilation tools; the first step is to install it and create a dedicated repository for toolchains that are to be built.

# install the packages
emerge crossdev
emerge eselect-repository

# create the dedicated repository
eselect repository create crossdev

# build the risc-v toolchain for baremetal binaries
crossdev --target riscv64-unknown-elf

Install QEMU for RISC-V

Gentoo allows to build a minimal RISC-V system emulator by setting QEMU_SOFTMMU_TARGETS in portage.use:

USE_FILE=/etc/portage/portage.use/qemu
echo 'app-emulation/qemu QEMU_SOFTMMU_TARGETS: riscv64 riscv32' >> $USE_FILE
emerge -a qemu

Setup in OpenBSD

The OpenBSD's package system already provides packages for the RISC-V GNU Toolchain and the QEMU system, so the needed tools can be installed by running:

pkg_add riscv-elf-newlib qemu gmake

Run the FreeRTOS demo

Once the toolchain and the emulator are installed, it's should be now possible to build and run the corresponding FreeRTOS "demo".

# fetch the FreeRTOS sources
git clone https://github.com/FreeRTOS/FreeRTOS.git --recurse-submodules

# build the demo targeted to the GNU Toolchain for RISC-V on QEMU
cd FreeRTOS/Demo/RISC-V-Qemu-virt_GCC
gmake

# run the demo
qemu-system-riscv32 -nographic -machine virt -net none \
-chardev stdio,id=con,mux=on -serial chardev:con \
-mon chardev=con,mode=readline -bios none \
-smp 4 -kernel ./build/RTOSDemo.axf

Terminate the emulation using the key combination Ctrl-a x.

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