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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
754 of 808
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 User Guide
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
for its attributes. The bit assignments are shown in
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.
4.4.3 SysTick Current Value Register
The VAL register contains the current value of the SysTick counter. See the register
summary in
for its attributes. The bit assignments are shown in
4.4.4 SysTick Calibration Value Register
The CALIB register indicates the SysTick calibration properties. See the register summary
in
for its attributes. The bit assignments are shown in
Table 648. 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
Table 649. 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 650. 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
.