1.4 Cortex-M3 Processor SysTick Timer

The processor has a 24-bit system timer, SysTick, that counts down from the reload value to zero, reloads, that is, wraps to the value in the SYST_RVR register on the next clock edge, and then counts down on subsequent clocks. The SysTick timer is used to generate a periodic interrupt to the Cortex-M3 processor. The SysTick can be polled by the software or it can be configured to generate an interrupt. The SysTick interrupt has its own entry in the vector table and therefore its own handler.