The SAM C21 ARM^® Cortex^®-M0+ Processor Core includes an optional System Timer Module (SysTick) that provides a simple, 24-bit clear-on-write, decrementing, wrap-on-zero counter with a flexible control mechanism.

This hardware may be configured to periodically generate an interrupt and trigger the following handler routine:

void SysTick_Handler(void){
...
}

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