SysTick Control and Status
| ENABLE | 1 : the counter will operate in a multi-shot manner. 0 : the counter is disabled |
| TICKINT | 1 : counting down to 0 will cause the SysTick exception to be pended. Clearing the SysTick Current Value register by a register write in software will not cause SysTick to be pended. 0 : counting down to 0 does not cause the SysTick exception to be pended. Software can use COUNTFLAG to determine if a count to zero has occurred. |
| CLKSRC | 1 : core clock used for SysTick. 0 : clock source is (optional) external reference clock |
| COUNTFLAG | Returns 1 if timer counted to 0 since last time this register was read. COUNTFLAG is set by a count transition from 1 to 0. COUNTFLAG is cleared on read or by a write to the Current Value register. |