4.4.4. SysTick Calibration Value Register

This register is optional and might not be available in your implementation.

The SYST_CALIB register indicates the SysTick calibration properties. See the register summary in Table 4.33 for its attributes. The bit assignments are:

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Table 4.37. SYST_CALIB bit assignments

BitsNameFunction[a]
[31]NOREF

Indicates whether the device provides a reference clock to the processor:

0

Reference clock provided.

1

No reference clock provided.

If your device does not provide a reference clock, the SYST_CSR.CLKSOURCE bit reads-as-one and ignores writes.

[30]SKEW

Indicates whether the TENMS value is exact:

0

TENMS value is exact.

1

TENMS value is inexact, or not given.

An inexact TENMS value can affect the suitability of SysTick as a software real time clock.

[29:24]-Reserved.
[23:0]TENMSReload value for 10ms (100Hz) timing, subject to system clock skew errors. If the value reads as zero, the calibration value is not known.

[a] The functions are implementation defined.


If calibration information is not known, calculate the calibration value required from the frequency of the processor clock or external clock.

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