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ac34856
Joined: 14 Dec 2009
Posts: 33
Location: Wales
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| Watchdog timer doesn't turn off 18F4620 PIC |
 Posted: Tue Feb 16, 2010 9:44 am |
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I'm having trouble getting the WDT to turn off. The following code
runs but the line setup_wdt(WDT_OFF) doesnt work - in other words the WDT still runs. I would also like to dynamically change the Watchdog timeout prescaler value other than in the fuses.
Compiler 4.057
Any comments appreciated.
| Code: |
#include <18F4620.h>
#device PASS_STRINGS=IN_RAM
#fuses HS // High speed oscillator
#fuses WDT // Watchdog timer enabled
#fuses WDT1024 // Watchdog timer prescaler
#fuses NOPROTECT
#fuses BROWNOUT // Has protection for recovery from low Vcc
#fuses PUT // Has power up timer
#fuses NOLVP // No Low voltage programming
#fuses MCLR
#fuses NODEBUG
#use DELAY(clock = 20000000, RESTART_WDT)
#use RS232(baud=115200, XMIT=PIN_C6, RCV=PIN_C7, ERRORS, STREAM=USB, RESTART_WDT)
TYPEDEF unsigned int16 UINT16;
UINT16 reason;
static UINT16 count;
void main(void)
{
reason = restart_cause();
switch(reason)
{ case WDT_TIMEOUT:
{ fprintf(USB, "\r\n Watchdog timed out - CPU Reset ! ");
break;
}
case NORMAL_POWER_UP:
{ fprintf(USB, "\r\n CPU Started normally !");
break;
}
default:
fprintf(USB, "\r\n Miscellaneous Restart (%04Xh)", reason);
break;
}
setup_wdt(WDT_OFF); // !!! Why doesnt this line work ??
while(1)
{
++count;
fprintf(USB, "\r\n A - Sleeping until WDT (Count: %Lu)", count);
delay_ms(10);
while(1); // Stop here waiting for WDT to test .. ..
// sleep(); // Go to sleep and wait for WDT to wake-up
fprintf(USB, "\r\n Woken up !");
// restart_wdt();
delay_ms(300);
}
} |
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Ttelmah
Guest
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| Posted: Tue Feb 16, 2010 11:20 am |
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Read the data sheet.....
Critical line:
"PIC18F2525/2620/4525/
4620 devices have a Watchdog Timer, which is either
permanently enabled via the configuration bits or
software controlled (if configured as disabled)."
You can only _software control_the watchdog timer, if it is _disabled_ in the fuses. If you set it to enabled in the fuses, it will _always_ run.
If you want to software control the 'effective' watchdog time, then have a timer interrupt, at a slightly higher frequency than your programmed watchdog time. Have an internal global variable called (say) wdog, then in the timer interrupt have:
| Code: |
if (wdog) {
--wdog;
restart_wdt();
}
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You can then in your code at any point set 'wdog' to a value, and have this many beats of the timer interrupt, plus the hardware watchdog time, till the watchdog will trigger.
Best Wishes |
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ac34856
Joined: 14 Dec 2009
Posts: 33
Location: Wales
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| Posted: Wed Feb 17, 2010 10:37 am |
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| Thanks .. that is an excellent piece of information ! |
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