The System Tick Timer (SYSTICK Timer) is a simple 24-bit down counter. The timer can be started and configured with an automatic reload value. If the timer is running and it's IRQ is enabled, it generates periodic interrupts. The System Tick Timer can use the internal clock (FCLK, the free running clock signal on the Cortex-M processor) or the external clock (the STCLK signal on the Cortex-M processor). The System Tick Timer is often used by the RTOS.
The System Tick Time (SysTick) generates interrupt requests on a regular basis. This allows an OS to carry out context switching to support multiple tasking. For applications that do not require an OS, the SysTick can be used for time keeping, time measurement, or as an interrupt source for tasks that need to be executed regularly.
