Datasheet

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

12.10.1.1SysTick Control and Status

Name: SYST_CSR

Access: Read-write

Reset: 0x000000000

The SysTick SYST_CSR register enables the SysTick features.

• COUNTFLAG: Count Flag

Returns 1 if the timer counted to 0 since the last time this was read.

• CLKSOURCE: Clock Source

Indicates the clock source:

0: External Clock.

1: Processor Clock.

• TICKINT

Enables a SysTick exception request:

0: Counting down to zero does not assert the SysTick exception request.

1: Counting down to zero asserts the SysTick exception request.

The software can use COUNTFLAG to determine if SysTick has ever counted to zero.

• ENABLE

Enables the counter:

0: Counter disabled.

1: Counter enabled.

When ENABLE is set to 1, the counter loads the RELOAD value from the SYST_RVR register and then counts down. On reach-

ing 0, it sets the COUNTFLAG to 1 and optionally asserts the SysTick depending on the value of TICKINT. It then loads the

RELOAD value again, and begins counting.

31 30 29 28 27 26 25 24

–

23 22 21 20 19 18 17 16

– COUNTFLAG

15 14 13 12 11 10 9 8

–

76543210

CLKSOURCE TICKINT ENABLE