Cortex-M3 Processor (Reference Material)
UG0331 User Guide Revision 15.0 120
3.7.3.2.1 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.
3.7.3.3 SysTick Current Value Register
The SYST_CVR register contains the current value of the SysTick counter. See the register summary in
Table 71, page 119 for its attributes. The bit assignments are:
Figure 48 • SYST_CVR Register Bit Assignments
3.7.3.4 SysTick Calibration Value Register
The SYST_CALIB register indicates the SysTick calibration properties. See the register summary in
Table 71, page 119 for its attributes. The bit assignments are:
Figure 49 • SYST_CALIB Register Bit Assignments
[23:0] RELOAD Value to load into the SYST_CVR register when the counter is enabled and
when it reaches 0, see Calculating the RELOAD Value, page 121.
Table 74 • SYST_CVR 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 75 • SYST_CALIB Register Bit Assignments
Bits Name Function
[31] NOREF Reads as one. Indicates that no separate reference clock is provided.
[30] SKEW Reads as one. Calibration value for the 10ms inexact timing is not
known because TENMS is not known. This can affect the suitability of
SysTick as a software real time clock.
Table 73 • SYST_RVR Register Bit Assignments (continued)
Bits Name Function
7(1065HVHUYHG
6.(:
125()
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