Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Data Sheet
Product codes
ATSAM4E-XPRO
263
SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
12.10.1.4 SysTick Calibration Value Register
Name:
SYST_CALIB
Access: Read/Write
Reset: 0x00003A98
The SysTick SYST_CSR 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: TENMS Value Verification
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 calibra-
tion value is not known.
tion value is not known.
The TENMS field default value is 0x00003A98 (15000 decimal).
In order to achieve a 1 ms timebase on SystTick, the TENMS field must be programmed to a value corresponding to the
processor clock frequency (in kHz) divided by 8.
processor clock frequency (in kHz) divided by 8.
For example, for devices running the processor clock at 48 MHz, the TENMS field value must be 0x0001770
(48000 kHz/8)
(48000 kHz/8)
.
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