Introduction

Linux kernel provided good readable timer operations in the code. ref timer

Some attributes of system timer in the kernel are:

1. It was not designed for time-critical kernel modules, as it takes much works during the tick, such like update jiffies, process accounting, RCU callback, _irq_work_etc.
2. Some throughput cared system was configed in the kernel configration with “NOHZ” option, Invoke the tick during the “IDLE” state will offset the impact of the kernel “NOHZ” configration. We just want to invoke the callback instead of wake up other staffs.
3. Nearly all the embedded SoC have their design with 2 or more counter-based HW timers, it was not wise design binding the periodic work to the system timer.

Write a simple Periodic-Timer-Service for the SoC with additional HW counters.

Some preconditions on this simple HW based timer framework are:

• The counter based HW timer can be programmed to generate the interrupt for fast handling attached events.
• Only periodic task was supported now.

Detail design

• Public timer API

  1. periodic_task_setup(void) // called during the init stage, init the needed data structures.
  2. periodic_task_add(cpu, period, (*action), data, *name) // add period task into service.
  3. periodic_task_remove(*task)/periodic_task_remove_all() // remove task from list.
  4. periodic_task_get_period(*task)/periodic_task_get_cpu(*task)/periodic_task_get_name(*task) //get method
  5. global_timer_send_sync() //send IPI to the another SMP processor.
  6. global_timer_proc() // called when interrupt happened

• Usage In the arch setup procedure, invoke periodic_task_setup(). Register the global_timer_proc() in timer irq handler.

• Implemention I put all the code into my Github repo link