Problem with developing custom device driver.

Hello, I have problem developing custom device driver. I've read the documentation, but I only got confused. Is there a simple tutorial on how to write device drivers ?

My device has one write, one read register and it's capable of generating IRQ signal. It should work likt this: programmer writes data to write register using standard IOWR macro, my device processes data and returns it into read register generating interrupt. My question is how to write interrupt service routine ? Sorry for simple questions, but I'm beginner in NIOS II systems (I've created some systems based on Xilinx Microblaze processor only).