difficult software problem

hello,

i use QUARTUS 5.0 NIOS 5.0

i have a difficult software problem, i think something is writing undefined

into memory, but i cannot find it (searching now for two days).

in the main function i have the following...

main() {

int ctime=0;

int ctimemax=0;

while(1) {

...

...

if(....) {

ctimemax=1000;

}

else {

ctimemax=5000;

}

if(ctime>ctimemax) { // at this point ctimemax is e.g. 0 or something undefined

....

}

...

}

i have seen that the register fp (which is used to access ctimemax,stw r2,20(fp),

is different from startup, when the error happens.

the main problem is, that if i insert or renmove some code elsewhere,

i cannot see the error again.

one problem i have seen is that i made a fault with timer interrupts,

but i don't know if this could cause the error.

i had a# define

# define ALARMTICKS(x) ((alt_ticks_per_second()*(x))/1000)

DWORD alarm_spst_callback_10ms (void* context) {

alarmflags|=ALARM_SP_10MS;

if(led_txrx_time>0) {

led_txrx_time--;

PIO_CBI(PIO_LED_BASE,LED_TX_RX);

}

else {

PIO_SBI(PIO_LED_BASE,LED_TX_RX);

}

if(dsptimeout) dsptimeout--;

return ALARMTICKS(10);

}

this inserted a multiplication and division in the interrupt

...

0x00806874 <alarm_spst_callback_10ms+160>: call 0x80c524 <__mulsi3>

0x00806878 <alarm_spst_callback_10ms+164>: mov r4,r2

0x0080687c <alarm_spst_callback_10ms+168>: movi r5,1000

0x00806880 <alarm_spst_callback_10ms+172>: call 0x80c504 <__udivsi3>

...

i changed this to get a constant for the return value,

i cannnot see the error in the main loop again,

but i think this was not the problem

could the multiplication and division in the interrupt cause my problem ?

any suggestions, how i can find this error ?

i have seen that there is now "Run time stack checking", how does it works?

thanks