ARM Compiler toolchain v4.1 for µVision Using the Compiler

Compiler Features
/* Declare PSR as a register variable for the "apsr" register */
register PSR apsr __asm("apsr");
void set_Q(void)
{
apsr.b.Q = 1;
}
See also Example 4-3.
Example 4-3 Clearing the Q flag in the APSR using a named register variable
register unsigned int _apsr __asm("apsr");
__forceinline void ClearQFlag(void)
{
_apsr = _apsr & ~0x08000000; // clear Q flag
}
Disassembly:
ClearQFlag
MRS
BIC
MSR
BX
r0,APSR ; formerly CPSR
r0,r0,#0x80000000
APSR_nzcvq,r0; formerly CPSR_f
lr
See also Example 4-4.
Example 4-4 Setting up stack pointers using named register variables
register unsigned int _control __asm("control");
register unsigned int _msp __asm("msp");
register unsigned int _psp __asm("psp");
void init(void)
{
_msp = 0x30000000;
_control = _control | 3;
_psp = 0x40000000;
}
// set up Main Stack Pointer
// switch to User Mode with Process Stack
// set up Process Stack Pointer
Disassembly, compiled using --cpu=7-M:
init
MOV
MSR
MRS
ORR
MSR
MOV
MSR
BX
r0,0x30000000
MSP,r0
r0,CONTROL
r0,r0,#3
CONTROL,r0
r0,#0x40000000
PSP,r0
lr
ARM DUI 0375C Copyright © 2007-2008, 2011 ARM. All rights reserved. 4-17
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