Linux Drivers

This repository contains source code for some Linux character device drivers that I developed as a part of the Linux drivers course at the University of Wroclaw (a.y. 2021-2022):

• driver_calc - driver of a simple arithmetic peripheral, that is capable of performing +,-,*,/ operations
• driver_litex_gpio - driver of a LiteX's GPIO device that counts the number interrupts raised from the device
• driver_si7021 - driver of Silabs' SI7021 humidity and temperature sensor, connected via I2C
• driver_iio_si7020 - IIO driver of Silabs' SI702x sensors. This driver was not written from stratch, only the on-chip heater support was added (link)
• driver_si7210 - IIO driver of Silabs' SI7210 magnetic sensor

All the drivers can be built and run on a Vexriscv processor that is emulated in Renode framework.

Prerequisites

Renode

This project uses a customized version of Renode, which is pinned as a submodule. All the prerequisites needed for building Renode from sources are described in the Renode's documentation In order to build it one can use the command:

make build-renode

Downloading the latest renode tarball is also possible, however this is less recommended since it would result in a limited functionality of some devices that I used in this repository.

wget https://dl.antmicro.com/projects/renode/builds/renode-latest.linux-portable.tar.gz
mkdir renode_portable
tar xf  renode-latest.linux-portable.tar.gz -C renode_portable --strip-components=1

Environment setup

• make build-buildroot - build rootfs.cpio initrd image. A 32-bit RISC-V toolchain is also built which can be later used to build the linux kernel, opensbi and the driver itself if there is no RISC-V toolchain available on the system. In order to use the buildroot toolchain, the PATH variable needs to be modified:

export PATH=${REPO_PATH}/build/buildroot/host/bin:${PATH}

• make build-linux - build a Linux kernel for RISC-V architecture.

• make build-opensbi - build OpenSBI bootloader.

Build and run

Build a selected driver

In any of the driver_* directories, the following commands can be used to build all the files required to emulate a specific driver and test it in Renode:

• make dtb - build the device tree blob, that is used by kernel to read the hardware configuration
• make modules - build the *.ko file, that is the kernel module (later loaded with insmod)
• make test - build the test application

One can also simply type make to build all the required targets.

Once all the files are built, one should also create a virtio image, which contains all the built files. This approach makes it easy to access the kernel module and test application from the emulated Linux system:

• make build-virtio - build the virtio image

Run Renode simulation

First, start Renode:

./build/renode/renode

Load the selected Renode script:

(monitor) include @driver_*/scripts/litex.resc

And finally start the emulation:

(machine-0) start