NXP Semiconductors LPC1768 - About IT Folding; CPUID Base Register; Interrupt Control and State Register

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User manual Rev. 3 — 20 December 2013 769 of 841
NXP Semiconductors
UM10360
Chapter 34: Appendix: Cortex-M3 user guide
34.4.3.2.1 About IT folding
In some situations, the processor can start executing the first instruction in an IT block
while it is still executing the
IT instruction. This behavior is called IT folding, and improves
performance, However, IT folding can cause jitter in looping. If a task must avoid jitter, set
the DISFOLD bit to 1 before executing the task, to disable IT folding.
34.4.3.3 CPUID Base Register
The CPUID register contains the processor part number, version, and implementation
information. See the register summary in Table 654
for its attributes. The bit assignments
are shown in Table 656
.
34.4.3.4 Interrupt Control and State Register
The ICSR:
• provides:
– a set-pending bit for the Non-Maskable Interrupt (NMI) exception
– set-pending and clear-pending bits for the PendSV and SysTick exceptions
• indicates:
– the exception number of the exception being processed
Table 655. ACTLR bit assignments
Bits Name Function
[31:3] - Reserved
[2] DISFOLD When set to 1, disables IT folding. see Section 34.4.3.2.1
for more
information.
[1] DISDEFWBUF When set to 1, disables write buffer use during default memory map
accesses. This causes all bus faults to be precise bus faults but
decreases performance because any store to memory must complete
before the processor can execute the next instruction.
Remark: This bit only affects write buffers implemented in the
Cortex-M3 processor.
[0] DISMCYCINT When set to 1, disables interruption of load multiple and store multiple
instructions. This increases the interrupt latency of the processor
because any LDM or STM must complete before the processor can
stack the current state and enter the interrupt handler.
Table 656. CPUID register bit assignments
Bits Name Function
[31:24] Implementer Implementer code:
0x41 = ARM
[23:20] Variant Variant number, the r value in the r
npn product revision identifier:
0x2 = r2p0
[19:16] Constant Reads as
0xF
[15:4] PartNo Part number of the processor:
0xC23 = Cortex-M3
[3:0] Revision Revision number, the p value in the r
npn product revision identifier:
0x0 = r2p0