Lpc2000

How big is your buffer?  To be specific, what value does kbbufsz have?

--
Paul Curtis, Rowley Associates Ltd   http://www.rowley.co.uk 
CrossWorks for ARM, MSP430, AVR, MAXQ, and now Cortex-M3 processors


> -----Original Message-----
> From: Peter Jakacki [mailto:peterjak@...] 
> Sent: 28 March 2006 09:03
> To: lpc2000@yahoogroups.com
> Subject: [lpc2000] ARM halfword bugs?
> 
> 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*
> 
> 
> 
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