Lpc2000

I came across a glitch in my PS/2 keyboard code where every 11th 
keystroke my system would experience some sort of corruption. I checked 
the code and I checked the code and everything looks right (it's 
assembler). Finally in desperation I changed the halfword store to 
buffer into a full word store and then incremented the index by 4 
instead of 2 and now it works perfectly. The buffer is on a word boundary.

Normally I wouldn't bother mentioning all this but I have had a few 
other episodes in the past somewhat similar to this before where I 
replaced the halfword stores with byte or word stores and everything 
works fine again.

I suspect the assembler as I have dissected other opcodes before and 
from memory I think I found problems in that the machine code was incorrect.

Could it be that there is a bug in the ARM core or the assembler? Does 
anyone know of similar problems?

CPU:   LPC2138/2148
TOOL:  IAR Workbench V4.10B

This works:
-------------------------
  106    0000D85C 0F412DE9     KBISR:  stmfd   
sp!,{r0-r3,MP,lr}               ;save regs
  107    0000D860 4084A0E3             ldr     MP,=RAM
  108    0000D864 CC001FE5     kbrdl:  ldr     r0,SPCRc
  109    0000D868 042090E5             ldr     
r2,[r0,#SPISR-SPCR]             ;check status
  110    0000D86C 800012E3             tst     
r2,#80h                         ;more data?
  111    0000D870 DBE3FF0A             beq     
EnableVIC                       ;return from
  112    0000D874 0110A0E3             mov     
r1,#1                           ;clear the int
  113    0000D878 1C10C0E5             strb    r1,[r0,#SPINT-SPCR]
  114    0000D87C 081090E5             ldr     
r1,[r0,#SPDR-SPCR]              ;read SPI data
  115    0000D880 34001FE5             ldr     
r0,=kbbuf                       ;skip 1st byte
  116    0000D884 4030D0E5             ldrb    r3,[r0,#kbwr-kbbuf]
  117    0000D888 002083E0             add     
r2,r3,r0                        ;point to write
  118    0000D88C 001082E5             str     
r1,[r2]                         ;save 32-bits
  119    0000D890 043083E2             add     r3,r3,#4
  120    0000D894 3F3003E2             and     r3,r3,#kbbufsz-1
  121    0000D898 4030C0E5             strb    r3,[r0,#kbwr-kbbuf]
  122    0000D89C F0FFFFEA             b       kbrdl  
-------------------------

This doesn't quite work:
-------------------------
  106    0000D85C 0F412DE9     KBISR:  stmfd   
sp!,{r0-r3,MP,lr}               ;save regs
  107    0000D860 4084A0E3             ldr     MP,=RAM
  108    0000D864 CC001FE5     kbrdl:  ldr     r0,SPCRc
  109    0000D868 042090E5             ldr     
r2,[r0,#SPISR-SPCR]             ;check status
  110    0000D86C 800012E3             tst     
r2,#80h                         ;more data?
  111    0000D870 DBE3FF0A             beq     
EnableVIC                       ;return from
  112    0000D874 0110A0E3             mov     
r1,#1                           ;clear the int
  113    0000D878 1C10C0E5             strb    r1,[r0,#SPINT-SPCR]
  114    0000D87C 081090E5             ldr     
r1,[r0,#SPDR-SPCR]              ;read SPI data
  115    0000D880 34001FE5             ldr     
r0,=kbbuf                       ;skip 1st byte
  116    0000D884 4030D0E5             ldrb    r3,[r0,#kbwr-kbbuf]
  117    0000D888 002083E0             add     
r2,r3,r0                        ;point to write
!!!!!!!! THIS LINE IS THE PROBLEM !!!!!!
  118    0000D88C B010C2E1             strh    
r1,[r2]                         ;save 16-bits
  119    0000D890 023083E2             add     r3,r3,#2
  120    0000D894 3F3003E2             and     r3,r3,#kbbufsz-1
  121    0000D898 4030C0E5             strb    r3,[r0,#kbwr-kbbuf]
  122    0000D89C F0FFFFEA             b       kbrdl  
-------------------------


*Peter*