NUC505-YO2Y datasheet(80/130 Pages) NUVOTON

80 / 130 page

NUC505

July. 26, 2018

Page 80 of 130

Rev.1.08

6.2.8

System Timer (Systick)

The Cortex

® -M4 includes an integrated system timer, SysTick, which provides a simple, 24-bit clear-

on-write, decrementing, wrap-on-zero counter with a flexible control mechanism. The counter can be

used as a Real Time Operating System (RTOS) tick timer or as a simple counter.

When system timer is enabled, it will count down from the value in the SysTick Current Value Register

(SYST_CVR) to zero, and reload (wrap) to the value in the SysTick Reload Value Register

(SYST_RVR) on the next clock cycle, and then decrement on subsequent clocks. When the counter

transitions to zero, the COUNTFLAG status bit is set. The COUNTFLAG bit clears on reads.

The SYST_CVR value is UNKNOWN on reset. Software should write to the register to clear it to zero

before enabling the feature. This ensures the timer will count from the SYST_RVR value rather than

an arbitrary value when it is enabled.

If the SYST_RVR is zero, the timer will be maintained with a current value of zero after it is reloaded

with this value. This mechanism can be used to disable the feature independently from the timer

enable bit.

For more detailed information, plea

se refer to the “ARM

® Cortex® -M4 Technical Reference Manual”

and “ARM

® v6-M Architecture Reference Manual”.

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