17.4.6 SysTick
SysTick is an internal interrupt used to handle interrupts raised by the
system timer. Its handler is SysTick_Handler with IRQ number
SysTick_IRQn, it is always enabled and has configurable priority. This
handler can also be triggered via software using the following code.
SCB->ICSR = SCB_ICSR_PENDSTSET_Msk;
