Perhaps this has already been found, but I've come across what looks
like an array indexing bug in msp430-gcc 4.5.3. My platform is Ubuntu
Natty, and I built this from source, using the directions at
https://github.com/sergiocampama/Launchpad/blob/master/README.md
I've tried to make a minimal example that demonstrates the bug. This
code was originally a program to do SPI with an LCD panel, but I've
trimmed almost everything. The functions write_ones() and
write_zeros() are essentially identical, except that the array in
write_ones() is marked volatile while the array in write_zeros() is
not. It is the write_zeros() function that shows the error, and I've
indicated it in the assembly that follows.
#include <msp430g2211.h>
#define RED BIT0
#define GRN BIT6
void spi_IO( unsigned char data[] ) {
if( data[0] == 5) { // show red light when called by ones() and
grn for zeros()
P1OUT |= RED;
P1OUT &= ~GRN;
} else {
P1OUT |= GRN;
P1OUT &= ~RED;
}
}
void write_zeros( void ) {
unsigned char zeros[17];
int j, page;
for( page = 0; page < 2; page++ ) {
zeros[0] = 6;
spi_IO( zeros );
for( j = 0; j < 17; j++ ) zeros[j] = 0x00;
spi_IO( zeros );
}
}
void write_ones( void ) {
volatile unsigned char ones[17];
int j, page;
for( page = 0; page < 2; page++ ) {
ones[0] = 5;
spi_IO( ones );
for( j = 0; j < 17; j++ ) ones[j] = 0xFF;
spi_IO( ones );
}
}
void main( void ) {
int i;
// Stop the watchdog timer so it doesn't reset our chip
WDTCTL = WDTPW + WDTHOLD;
// These are the pins we need to drive.
P1DIR |= RED + GRN;
P1OUT |= RED + GRN;
for( i = 0; i < 20; i++ ) {
__delay_cycles( 30000 );
}
P1OUT &= ~(RED + GRN);
write_ones();
write_zeros();
P1OUT &= ~(RED + GRN);
for( ;; ) {
__bis_SR_register( LPM3_bits + GIE );
}
}
I built it and sent it to a Launchpad with these commands:
$ /usr/local/bin/msp430-gcc -S -O2 -mmcu=msp430g2211 -o minimal.s minimal.c
$ /usr/local/bin/msp430-gcc -O2 -mmcu=msp430g2211 -o minimal.elf minimal.s
$ mspdebug rf2500 "prog minimal.elf"
The bug is in the write_zeros() function. In the assembly code, the
array bound is set to 17 instead of 17+base pointer.
.file "minimal.c"
.arch msp430g2211
.cpu 430
.mpy none
.text
.p2align 1,0
.global spi_IO
.type spi_IO,@function
/***********************
* Function `spi_IO'
***********************/
spi_IO:
cmp.b #5, @r15
jeq .L5
bis.b #64, &__P1OUT
and.b #llo(-2), &__P1OUT
ret
.L5:
bis.b #1, &__P1OUT
and.b #llo(-65), &__P1OUT
ret
.Lfe1:
.size spi_IO,.Lfe1-spi_IO
;; End of function
.p2align 1,0
.global write_zeros
.type write_zeros,@function
/***********************
* Function `write_zeros'
***********************/
write_zeros:
push r11
push r10
push r9
add #llo(-18), r1
mov #2, r9
mov r1, r11
mov #17, r10 ;<------------ right here. Needs another
instruction: add r11, r10
.L8:
mov.b #6, @r1
mov r11, r15
call #spi_IO
mov r11, r15
.L7:
mov.b #0, @r15
add #1, r15
cmp r10, r15 ;<------------- because here we compare the
index pointer to it
jne .L7
mov r11, r15
call #spi_IO
add #llo(-1), r9
jne .L8
add #18, r1
pop r9
pop r10
pop r11
ret
.Lfe2:
.size write_zeros,.Lfe2-write_zeros
;; End of function
.p2align 1,0
.global write_ones
.type write_ones,@function
/***********************
* Function `write_ones'
***********************/
write_ones:
push r11
add #llo(-18), r1
mov #2, r11
.L13:
mov.b #5, @r1
mov r1, r15
call #spi_IO
mov #0, r15
.L12:
mov r1, r14
add r15, r14
mov.b #llo(-1), @r14
add #1, r15
cmp #17, r15
jne .L12
mov r1, r15
call #spi_IO
add #llo(-1), r11
jne .L13
add #18, r1
pop r11
ret
.Lfe3:
.size write_ones,.Lfe3-write_ones
;; End of function
.section .init9,"ax",@progbits
.p2align 1,0
.global main
.type main,@function
/***********************
* Function `main'
***********************/
main:
mov #23168, &__WDTCTL
bis.b #65, &__P1DIR
bis.b #65, &__P1OUT
mov #20, r15
.L17:
nop
mov #9999, r14
.L__delay__111:
dec r14
jnz .L__delay__111
add #llo(-1), r15
jne .L17
and.b #llo(-66), &__P1OUT
call #write_ones
call #write_zeros
and.b #llo(-66), &__P1OUT
.L18:
bis #216, r2
jmp .L18
.Lfe4:
.size main,.Lfe4-main
;; End of function
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