Current Program Status Register exception modes

问题:

I'm working with code that has the following four assembly instructions:

CPSR_cxsf
SPSR_cxsf

CPSR_c
SPSR_c

I've been having a hard time trying to figure out what the difference between these exception modes is. Can anyone advice?

回答1:

c, x, s and f refers to the different parts of the status registers:

c = Control
x = eXtension
s = Status
f = Flags

The purpose of using e.g. CPSR_c is that it allows you to update only parts of the status register (in this case the control bits) without affecting the other parts.