Mastering Linux Kernel Development

Programmable interrupt timer (PIT)

There are certain tasks that need to be carried out by the kernel at regular intervals, such as:

• Updating the current time and date (at midnight)
• Updating the system running time (uptime)
• Keeping track of the time consumed by each process so that they don't exceed the time allotted to run on the CPU
• Keeping track of various timer activities

In order to carry out these tasks, interrupts must be periodically raised. Every time this periodic interrupt is raised, the kernel knows it's time to update the aforementioned timing data. The PIT is the piece of hardware responsible for issuing this periodic interrupt, called timer interrupt. The PIT keeps on issuing timer interrupts on IRQ0 periodically at approximately ...