Systick Calibration Value Register (Stk_Calib) - ST STM32F0 Series Programming Manual

Core peripherals
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.
31 30 29 28
NO
SKEW
REF
r r
15 14 13 12
r r r
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
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:
1. Program reload value.
2. Clear current value.
3. Program Control and Status register.
88/91
27 26 25
Reserved
11 10 9
r r r r
Doc ID 022979 Rev 1
24 23 22 21
r r r
8 7 6 5
TENMS[15:0]
r r r r
20 19 18 17
TENMS[23:16]
r r r
4 3 2 1
r r r
PM0215
16
r r
0
r r