SysTick-Based Timing Provider

Description

This is auxiliary implementation of Timing provider API using ARM SysTick.

This file can serve both as an example of how to implement timing provider and also serve as quick bootstrap timing provider for your project. You'll have to replace it if you want to either go tickless or implement power management.

This implementation uses SysTick Cortex-M peripheral available on virtually all ARM Cortex-M microcontrollers. The implementation here is a simple timer that fires periodically. This will disable kernel's tickless feature.

Functions
void	timing_provider_setup (int interval_ms)
	Setup the timing provider.
void	sys_tick_handler ()
	SysTick interrupt handler.

Function Documentation

sys_tick_handler()

void sys_tick_handler

(

)

SysTick interrupt handler.

This ISR serves SysTick interrupt. It contains a counter, how many more interrupts have to happen before kernel gets called. If counter reaches zero, then kernel is called. Return value from kernel denotes next delay before kernel shall be called again. If that value is zero, then systick timer is disabled. Otherwise the counter is restored with new value and cycle repeats again.

Different timing provider may choose to use different clock provider, or even providers and decide, that it will put CPU into sleep mode, if delay is too long, or there is no expected timed wake-up. If timing provider behaves as this, it is integrator's responsibility to ensure, that external interrupts, or whatever other sources of events are enabled in sleep state, which the timing provider will enter.

Kernel never calls this function on its own. Integrator may use whatever means of triggering the timer appropriate for given hardware. Whatever implementation provided must call kernel callback os_sched_timing_callback from kernel-equivalent context.

timing_provider_setup()

void timing_provider_setup

(

int

interval_ms

)

Setup the timing provider.

This function shall be called by the main() function during hardware bringup. Its purpose is to configure whatever peripheral or combination of peripherals that provides kernel timing services. These peripherals shall be configured and prepared, but not launched yet.

Kernel never calls this function on its own. The prototype of this function can be modified by the integrator to suit all the needs.

This function shall be called before the os_start() function is called and can therefore be called in any suitable context.

Parameters

[in]

interval_ms

how often the systick ISR shall be called.