SAM4S_14 Datasheet, PDF (233/1231 Pages) ATMEL Corporation – ARM-based Flash MCU

12.10 System Timer (SysTick)
The processor has a 24-bit system timer, SysTick, that counts down from the reload value to zero, reloads (wraps
to) the value in the SYST_RVR on the next clock edge, then counts down on subsequent clocks.
When the processor is halted for debugging, the counter does not decrement.
The SysTick counter runs on the processor clock. If this clock signal is stopped for low power mode, the SysTick
counter stops.
Ensure that the software uses aligned word accesses to access the SysTick registers.
The SysTick counter reload and current value are undefined at reset; the correct initialization sequence for the
SysTick counter is:
1. Program the reload value.
2. Clear the current value.
3. Program the Control and Status register.
SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
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