How to implement virtual hardware in QEMU?

Hello everyone, I want to implement some virtual hardware in QEMU for driver testing. For example, to implement a timer which sends interrupt to CPU periodically. However, I can't find any documentation which details the interfaces and the framework. The only clue is the `hw` directory in the source tree of QEMU, but it is so complex for a beginners to start up. So, are there helpful videos or articles? Regards!