2.7.3.4 SysTick Calibration Value Register

The SYST_CALIB register indicates the SysTick calibration properties. See the register summary in Table 2-65 for its attributes. The bit assignments are:

Figure 2-44. SYST_CALIB Register Bit Assignments

Table 2-69. SYST_CALIB Register Bit Assignments
Bits	Name	Function
[31]	NOREF	Reads as one. Indicates that no separate reference clock is provided.
[30]	SKEW	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.
[29:24]		Reserved.
[23:0]	TENMS	Reads as zero. Indicates calibration value is not known.

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