Just to preface, this was done as an educational exercise. There are great existing user space libraries for interfacing with the well-loved st7036 chipset. However, I thought it would be an interesting challenge to write a kernel module for raspberry pi that implemented a character device driver at the register level. Previously, I wrote a driver for this display for stm32, so my goal was to focus on the kernel aspects rather than the interface, which I copied with few changes.

This project, like many others, involved more reading than coding or building. Thankfully, there was great information to be found online, in places such as the Linux Device Drivers book and the Broadcom peripherals datasheet. There were a few topics that were not well documented, such as the creation of /dev entries and which of the several delay functions to use for a given scenario, but after some searching I found answers to these as well. As for the driver itself, it has a fairly standard topology. On module initialization, a virtual memory page for the GPIO registers is mapped, and startup commands are sent to the screen. Since Raspbian supports it, udev is utilized to create the /dev entry for the character device. Reads simply return a static message, and writes are sent over the bus to the screen one nibble at a time. While the operations in this driver are basic, I think it was a good starting place for kernel-side development. I hope to work on a network or block device driver, and utilize more advanced features in the future. The code for this driver is here. Included in the repository is a small script to write to the screen from stdin.