68300

Hello everyone,
 
When an interrupt occurs, the following happens:
 
1.  some stuff is put on the stack
2.  the interrupt acknowledgement cycle occurs
3. either AVEC or DSACK is used to terminate the IACK cycle
4.  the Interrupt Service Routine is entered.
 
If nothing terminates the IACK cycle, the machine will just hang there and no further bus activity or instruction fetches occur.
 
If the IACK cycle is terminated with BERR (either external or from the internal Bus Error Monitor) a spurious interrupt exception will be taken.
 
 
 
Here is a question for the person having the problem.  What happens when IRQ7 occurs?  Does program execution continue, does program execution appear to stop, or what?
 
If program execution appears to stop, the problem is almost certainly that there is no AVEC or DSACK for the Interrupt Acknowledgement Cycle.
 
You can get an internall AVEC or DSACK by programming the chip select logic.  Program the Base Address Register to $FFF8, and program the Option Register for ASYNC, BOTH BYTES,  READ and WRITE, AS, zero wait states, CPU space, IPL field = %000 for all interrupts or put in the interrupt level you want to respond to, AVEC = 1 for autovector, AVEC = 0 for DSACK.
 
REgards,
 
Charlie

-----Original Message-----
From: Scott Newell [mailto:newell@...]
Sent: Wednesday, July 16, 2003 12:51 PM
To: 68300@yahoogroups.com
Subject: RE: [68300] IRQ7 acting odd


>Would this prevent the interrupt from firing in the first place?

I've never used anything other than autovector interrupts, so I'm not
really sure.  I would have guessed (and this is just a guess) that it would
have either hung waiting for the external vector to be presented, or that
it would have used floating data bus lines as a vector, maybe ending in
some kind of bus fault.  Without an interrupt ack, I would not have guessed
that you'd be able to run at all after /IRQ7 went low.


>(I'm not avoiding trying out the extra chip select setup, I'm just waiting 
>to get time on the hardware).

I'm just waiting for Mr. Melear to weigh in on this one again... ;-)


newell



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