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Interrupt handling

 
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xpercad
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Interrupt handling
PostPosted: Thu Jun 24, 2004 5:53 pm     Reply with quote
I am using PIC18F452 and PCWH 3.202 and two interrupt sources (INT_EXT0 and TIMER_0).

INT_EXT0 is used for servicing an SPI interfaced decoder, and TIMER_0 is used for timing functions. My application requires that the service routine for TIMER_0 should be interrupted if INT_EXT0 becomes active. The service routine for INT_EXT0 is not "very" fast and a bit complex. From what I have read, using the FAST directive is a dangerous matter.

Can anybody shed some light as to how to handle this situation ???

Any kind of help will ge highly appreciated !!!

Aaron
Ttelmah
Guest
Re: Interrupt handling
PostPosted: Fri Jun 25, 2004 2:37 am     Reply with quote
xpercad wrote:
I am using PIC18F452 and PCWH 3.202 and two interrupt sources (INT_EXT0 and TIMER_0).

INT_EXT0 is used for servicing an SPI interfaced decoder, and TIMER_0 is used for timing functions. My application requires that the service routine for TIMER_0 should be interrupted if INT_EXT0 becomes active. The service routine for INT_EXT0 is not "very" fast and a bit complex. From what I have read, using the FAST directive is a dangerous matter.

Can anybody shed some light as to how to handle this situation ???

Any kind of help will ge highly appreciated !!!

Aaron

FAST, is OK, _provided you have a recent chip_. The problem is that there is a hardware fault with the first couple of years production of the chips, which prevents fast interrupts from reliably working where the source is asynchronous (an external event is).
Also when using fast, you become responsible for saving and restoring the registers.
Given the event is not 'very' fast, can't you just rely on the normal handling?. If you use the priority statement, the external interrupt can be set to be handled 'ahead' of the timer interrupt. Alternatively, assuming your interrupt routines are well written (_short_), perhaps only setting a flag, then add a test at the end of the timer routine, and if the external interrupt has occured set the flag for this here, and clear the interrupt flag, which avoids the time delay involved in exiting this routine before the second interrupt handler is called.

Best Wishes
xpercad
Guest
PostPosted: Fri Jun 25, 2004 8:25 am     Reply with quote
Thanks a lot for your advise and best wishes to you too !!!
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