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LI JUN
Note: This was originally posted on 26th April 2010 at http://forums.arm.com

code:
void __irq IRQ_Timer(void)
{

[0xe92d503f]   stmfd    r13!,{r0-r5,r12,r14}
    
           if((IO0PIN&U0)&&(T1IR&0x40))  
[0xe59f39ac]   [color="#FF0000"]ldr      r3,0x0000132c ; = #0xe0028000[/color]
[0xe5930000]   [color="#FF0000"]ldr      r0,[r3,#0][/color]
[0xe3100b80]   tst      r0,#0x20000
[0xe59f099c]   ldr      r0,0x00001328 ; = #0x40000004             
[0xe3a0c055]   mov      r12,#0x55
[0xe2431b80]  [color="#FF0000"] sub      r1,r3,#0x20000[/color]
[0x0a000014]   beq      0x9e8  ; (IRQ_Timer + 0x74)
[0xe5912000]   ldr      r2,[r1,#0]
[0xe3120040]   tst      r2,#0x40
[0x0a000011]   beq      0x9e8  ; (IRQ_Timer + 0x74)
  
ram data:
0x00001320  E000C000 E0034000 40000004 [color="#FF0000"]E0028000[/color]
0x00001330  00003092 00002710 40000044 000008D4
0x00001340  4000001C 40000000 00000974 000030A2

i have defined the[color="#FF0000"] T1IR [/color]and [color="#FF0000"]IO0PIN[/color] by macro,but i find the mcu gets the register address from ram , please look at the ram data.and i use the lpc2138.
please help me!
Parents
  • Arm Employee Badge
    Note: This was originally posted on 26th April 2010 at http://forums.arm.com

    The ARM instructions can only encode an 8-bit literal rotated an even number of places - if the value cannot be encoded in that then most compilers fall back on loading the constant from memory. In your case the constants 0xe0028000 cannot be encoded in 8-bits rotated, so the compiler has fallen back on loading from memory.

    FYI: The ARMv7 architecture (ARM and Thumb2) includes a pair of wide-move instructions for putting a 16-bit value into either the high or the low halves of a register, which would help in this case, , although code-size can be larger. Newer micro-controllers based on the Cortex-M family include these instructions.
Reply
  • Arm Employee Badge
    Note: This was originally posted on 26th April 2010 at http://forums.arm.com

    The ARM instructions can only encode an 8-bit literal rotated an even number of places - if the value cannot be encoded in that then most compilers fall back on loading the constant from memory. In your case the constants 0xe0028000 cannot be encoded in 8-bits rotated, so the compiler has fallen back on loading from memory.

    FYI: The ARMv7 architecture (ARM and Thumb2) includes a pair of wide-move instructions for putting a 16-bit value into either the high or the low halves of a register, which would help in this case, , although code-size can be larger. Newer micro-controllers based on the Cortex-M family include these instructions.
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