Datasheet

209
SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
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 register 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.
12.10.1 System Timer (SysTick) User Interface
Table 12-34. System Timer (SYST) Register Mapping
Offset Register Name Access Reset
0xE000E010 SysTick Control and Status Register SYST_CSR Read-write 0x00000004
0xE000E014 SysTick Reload Value Register SYST_RVR Read-write Unknown
0xE000E018 SysTick Current Value Register SYST_CVR Read-write Unknown
0xE000E01C SysTick Calibration Value Register SYST_CALIB Read-only 0xC0000000