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ATSAM4S-XPLD
213
SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
12.10.1.4SysTick Calibration Value Register
Name:
SYST_CALIB
Access: Read-write
Reset: 0x000000000
The SysTick SYST_CSR register indicates the SysTick calibration properties.
• NOREF: No Reference Clock
It 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.
• SKEW
It 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.
• TENMS: Ten Milliseconds
The reload value for 10 ms (100 Hz) timing is subject to system clock skew errors. If the value reads as zero, the calibration value
is not known.
is not known.
Read as 0x000030D4. The SysTick calibration value is fixed at 0x000030D4 (8000), which allows the generation of a time base of
1 ms with SysTick clock at 12.5 MHz (100/8 = 12.5 MHz).
1 ms with SysTick clock at 12.5 MHz (100/8 = 12.5 MHz).
31
30
29
28
27
26
25
24
NOREF
SKEW
–
23
22
21
20
19
18
17
16
TENMS
15
14
13
12
11
10
9
8
TENMS
7
6
5
4
3
2
1
0
TENMS