| 2017-02-23 23:52:08 |
fcayci |
description |
Hi
I am working on writing assembly for a Cortex-M3 chip, and I just came across something interesting. When I try to compile `ldr r8, = #20` the assembler generates `cmp r0, #20` instruction. This happens for all the high registers. I don't know if this is an intended behavior or not, but it doesn't happen for higher numbers (> 255) and mov instruction. For example:
ldr r8, = #1245 - works fine
mov r8, #20 - works fine
ldr r8, = #20 - do not work.
I use the following to compile.
arm-none-eabi-as.exe -mcpu=cortex-m3 -mthumb .\temp.s -o temp.elf
Here is the part of the code:
.thumb
.syntax unified
...
_start:
ldr r5, = #1234
ldr r4, = #1234
ldr r8, = #20
mov r8, #20
ldr r3, = #1000
Here is what it generates:
00000008 <_start>:
8: f240 45d2 movw r5, #1234 ; 0x4d2
c: f240 44d2 movw r4, #1234 ; 0x4d2
10: 2814 cmp r0, #20
12: f04f 0814 mov.w r8, #20
16: f44f 737a mov.w r3, #1000 ; 0x3e8
Can you please advise?
Thanks,
Furkan |
Hi
I am working on writing assembly for a Cortex-M3 chip, and I just came across something interesting. When I try to compile `ldr r8, = #20` the assembler generates `cmp r0, #20` instruction. This happens for all the high registers. I don't know if this is an intended behavior or not, but it doesn't happen for higher numbers (> 255) and mov instruction. For example:
ldr r8, = #1245 - works fine
mov r8, #20 - works fine
ldr r8, = #20 - do not work.
I use the following to compile.
arm-none-eabi-as.exe -mcpu=cortex-m3 -mthumb .\temp.s -o temp.elf
Here is the part of the code:
.thumb
.syntax unified
...
_start:
ldr r5, = #1234
ldr r4, = #1234
ldr r8, = #20
mov r8, #20
ldr r3, = #1000
Here is what it generates:
00000008 <_start>:
8: f240 45d2 movw r5, #1234 ; 0x4d2
c: f240 44d2 movw r4, #1234 ; 0x4d2
10: 2814 cmp r0, #20
12: f04f 0814 mov.w r8, #20
16: f44f 737a mov.w r3, #1000 ; 0x3e8
Can you please advise?
arm-none-eabi-as.exe --version
GNU assembler (GNU Tools for ARM Embedded Processors) 2.26.2.20160923
Thanks,
Furkan |
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