Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet
Product codes
ATSAM4S-WPIR-RD
SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
238
12.10.1.4SysTick Calibration Value Register
Name:
SYST_CALIB
Access:
Read
/Write
Reset:
0x00
0030D4
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.
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.
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.
The TENMS field default value is 0x000030D4 (12500 decimal).
In order to achieve a 1 ms timebase on SystTick, the TENMS field must be programmed to a value corresponding to the
The TENMS field default value is 0x000030D4 (12500 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.
For example, for devices running the processor clock at 48 MHz, the TENMS field value must be 0x0001770
For example, for devices running the processor clock at 48 MHz, the TENMS field value must be 0x0001770
(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