UM10429
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User manual
Rev. 1 — 20 October 2010
238 of 258
NXP Semiconductors
UM10429
Chapter 19: Appendix LPC1102 ARM Cortex-M0 reference
19.5.3.7.2
System Handler Priority Register 3
The bit assignments are:
19.5.3.8 SCB usage hints and tips
Ensure software uses aligned 32-bit word size transactions to access all the SCB
registers.
19.5.4 System timer, SysTick
When enabled, the timer counts down from the current value (SYST_CVR) to zero,
reloads (wraps) to the value in the SysTick Reload Value Register (SYST_RVR) on the
next clock edge, then decrements on subsequent clocks. When the counter transitions to
zero, the COUNTFLAG status bit is set to 1. The COUNTFLAG bit clears on reads.
Remark:
The SYST_CVR value is UNKNOWN on reset. Software should write to the
register to clear it to zero before enabling the feature. This ensures the timer will count
from the SYST_RVR value rather than an arbitrary value when it is enabled.
Remark:
If the SYST_RVR is zero, the timer will be maintained with a current value of
zero after it is reloaded with this value. This mechanism can be used to disable the feature
independently from the timer enable bit.
A write to the SYST_CVR will clear the register and the COUNTFLAG status bit. The write
causes the SYST_CVR to reload from the SYST_RVR on the next timer clock, however, it
does not trigger the SysTick exception logic. On a read, the current value is the value of
the register at the time the register is accessed.
Remark:
When the processor is halted for debugging the counter does not decrement.
The system timer registers are:
[1]
SysTick calibration value.
Table 228. SHPR2 register bit assignments
Bits
Name
Function
[31:24]
PRI_11
Priority of system handler 11, SVCall
[23:0]
-
Reserved
Table 229. SHPR3 register bit assignments
Bits
Name
Function
[31:24]
PRI_15
Priority of system handler 15, SysTick exception
[23:16]
PRI_14
Priority of system handler 14, PendSV
[15:0]
-
Reserved
Table 230. System timer registers summary
Address
Name
Type
Reset
value
Description
0xE000E010
SYST_CSR
RW
0x00000000
0xE000E014
SYST_RVR
RW
Unknown
0xE000E018
SYST_CVR
RW
Unknown
0xE000E01C
SYST_CALIB RO
0x00000004