Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos
Los códigos de productos
ATSAM4S-XPLD
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.
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.
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:
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