ARM Cortex-M processor systick timer

 

The SysTick timer is commonly used as the tick timer for RTOS schedulers, providing a base for scheduling tasks at regular intervals. The SysTick timer is a 24-bit countdown timer built into all ARM Cortex-M processors. It's designed to generate periodic interrupts, often used for tasks like real-time operating system (RTOS) ticking or as a general-purpose timer. It counts down from a reload value, and when it reaches zero, it triggers an interrupt and reloads the value to start the countdown again. Once the counter reaches zero, it automatically reloads the value from the SYST_RVR register, allowing it to repeat the counting process. The default clock source for the SysTick timer is the processor clock, but some devices may allow switching to a different clock source.