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Audi80
Joined: 07 Sep 2007
Posts: 41
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| Watchdog interrupt |
 Posted: Mon Aug 23, 2010 3:08 pm |
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Hi there, im using a PIC18F4620 with a watchdog at 4s, my problem is that i need to know when the wdt reset occurs to save some variables in the eeprom. Is there any interrupt or any other way that allows me to know that?
Thanks in advance... |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Mon Aug 23, 2010 11:23 pm |
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The WDT can perform a wakeup from sleep or a reset, not an interrupt. The WDT reset can be identified however
at the main() entry by querying restart_cause(). If #zero_ram isn't in effect, you can still save data at this time. |
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Audi80
Joined: 07 Sep 2007
Posts: 41
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| Posted: Tue Aug 24, 2010 5:52 am |
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Hi there FvM, i don't know what #zero_ram is but if i restart my application all variables like an int go to zero? For example:
| Code: |
int a = 0;
int main(){
printf("Value: %d\r\n",a);
// After wdt reset a goes to 0 or stays at 1????
a = 1;
return 0;
}
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Thanks in advance. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19328
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| Posted: Tue Aug 24, 2010 10:07 am |
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First, you are setting a to zero, so 'of course' it'll go to zero.
#zero_ram is a directive to tell the compiler to completely 'wipe' the RAM memory on boot.
However, if you change your code to:
| Code: |
void main(void){ //In CCS, the 'main' function is the code, and cannot
//return anything....
int a; //Declare, but don't initialise the variable
if (restart_cause() == WDT_TIMEOUT) {
printf("Watchdog restart - a=%d\n\r",a);
}
else {
a=0; //Initialise the variable
printf("Booted\n\r");
}
a++; //Increment a
while (TRUE) ; //Wait here for a watchdog
//Main cannot 'return' anything
}
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This will tell you that the watchdog has timed out, and print the value, which will increment each time it restarts.
However, in your 'write the EEPROM, on a watchdog, be aware of the limited write life of the EEPROM. If you are doing this every 4 seconds, depending on the chip involved, you could kill the EEPROM in under 12 hours.
Also, be aware of the inaccuracy of the watchdog. Typically there is a 3:1 variation in the 'real' time involved in a watchdog timeout...
Best Wishes |
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Audi80
Joined: 07 Sep 2007
Posts: 41
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| Posted: Tue Aug 24, 2010 10:24 am |
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Hi there Ttelmah first let me thank you for your reply.
I have developed a project that controls IO's a temperature sensor and also a RTCC and it communicates by RS485 and I have a server pooling every controller (10 by the way). Each controller is pooled every 2 sec and it restarts the wdt. Now what I want to do is that if the communication stops the wdt will reset. I want to save the data from the rtcc and the temperature sensor only if the last read data differs by 1 month.
So I don't think I will blow up the eeprom. I will try it later and see if it works.
Once again thanks... |
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