UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 20 December 2013 785 of 841
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 user guide
34.4.4.2 SysTick Reload Value Register
The LOAD register specifies the start value to load into the VAL register. See the register
summary in Table 674
for its attributes. The bit assignments are shown in Table 676.
34.4.4.2.1 Calculating the RELOAD value
The RELOAD value can be any value in the range
0x00000001
-
0x00FFFFFF
. A start value of
0 is possible, but has no effect because the SysTick exception request and COUNTFLAG
are activated when counting from 1 to 0.
The RELOAD value is calculated according to its use:
• To generate a multi-shot timer with a period of N processor clock cycles, use a
RELOAD value of N-1. For example, if the SysTick interrupt is required every 100
clock pulses, set RELOAD to 99.
• To deliver a single SysTick interrupt after a delay of N processor clock cycles, use a
RELOAD of value N. For example, if a SysTick interrupt is required after 400 clock
pulses, set RELOAD to 400.
34.4.4.3 SysTick Current Value Register
The VAL register contains the current value of the SysTick counter. See the register
summary in Table 674
for its attributes. The bit assignments are shown in Table 677.
34.4.4.4 SysTick Calibration Value Register
The CALIB register indicates the SysTick calibration properties. See the register summary
in Table 674
for its attributes. The bit assignments are shown in Table 678.
Table 676. LOAD register bit assignments
Bits Name Function
[31:24] - Reserved.
[23:0] RELOAD Value to load into the VAL register when the counter is
enabled and when it reaches 0, see Section 34.4.4.2.1
.
Table 677. VAL register bit assignments
Bits Name Function
[31:24] - Reserved.
[23:0] CURRENT Reads return the current value of the SysTick counter.
A write of any value clears the field to 0, and also clears the
SysTick CTRL.COUNTFLAG bit to 0.
Table 678. CALIB register bit assignments
Bits Name Function
[31] NOREF Indicates whether a separate reference clock is available. This value is
factory preset as described in Section 23.1
.
[30] SKEW Indicates whether the value of TENMS is precise. This can affect the
suitability of SysTick as a software real time clock. This value is factory
preset as described in Section 23.1
.
[29:24] - Reserved.
[23:0] TENMS This value is factory preset as described in Section 23.1
.
To Next Page
Loading...
Need help?
General
