Pick a simple driver (for example, for a serial device / UART; [0] should be the Raspberry Pi's UART); prefer ARM, since this is more straightforward. From ther

Pick a simple driver (for example, for a serial device / UART; [0] should be the Raspberry Pi's UART); prefer ARM, since this is more straightforward. From there, you can work your way up from how data arrives in controller registers, to how the driver handles the interrupt (you'll learn about ISRs and DSRs and how to read a microcontroller datasheet), to how the driver notifies the application program thread waiting on the data (you'll learn about scheduling), to how the read syscall transfers memory from kernel space to userspace. I'd not recommend diving directly into the network driver stack, since this has a lot or intermediary layers that do not further basic understanding[1]. Perhaps you should first try to get familiar with the Linux kernel's way of doing OO in C (if you are unfamiliar with this style; if you have done any modern C programming, it should not be a problem). (Do not start with the platform startup code; this would probably be too much for the start.) [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/tty/serial/amba-pl011.c?h=v4.12-rc3 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin... (maybe a bit too complex, since it uses DMA) [1] To be fair, the serial I/O layer has the tty layer as intermediary, so it's admittedly only slightly better