PM0215 datasheet(88/91 Pages) STMICROELECTRONICS

88 / 91 page

Core peripherals

PM0215

88/91

Doc ID 022979 Rev 1

4.4.4

SysTick calibration value register (STK_CALIB)

Address offset: 0x0C

Reset value: 0x0000000

The CALIB register indicates the SysTick calibration properties. If calibration information is

not known, calculate the calibration value required from the frequency of the processor clock

or external clock.

4.4.5

SysTick design hints and tips

The SysTick counter runs on the processor clock. If this clock signal is stopped for low

power mode, the SysTick counter stops.

Ensure 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:

Program reload value.

Clear current value.

Program Control and Status register.

REF

SKEW

Reserved

TENMS[23:16]

rrr

4321

TENMS[15:0]

rrr

Bit 31 NOREF: NOREF flag. Reads as one. Indicates that no separate reference clock is provided.

Bit 30 SKEW: SKEW flag: Reads as one. Calibration value for the 10ms inexact timing is not known

because TENMS is not known. This can affect the suitability of SysTick as a software real time

clock.

Bits 29:24 Reserved, must be kept cleared.

Bits 23:0 TENMS[23:0]: Calibration value. Reads as zero. Indicates calibration value is not known

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