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LI JUN over 12 years ago

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!

LI JUN over 12 years ago

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

register     address
IO0PIN     0xe0028000
T1IR         0xe0008000
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LI JUN over 12 years ago

Note: This was originally posted on 6th May 2010 at http://forums.arm.com

first, thank you very much.
i see.
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Simon Craske over 12 years ago

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

There doesn't appear to be anything fundamentally wrong with what the compiler has done;
optimising for space, this is likely to be the best option.

It is possible that speed may be improved by generating the address via MOV and ADD,
are you compiling with -Otime or -Ospace?

hth
s.
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Peter Harris over 12 years ago

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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