On Dec 7, 2008, at 2:43 PM, solarwind wrote:

> I do not know how to cause an interrupt on a pin change.

Dom says you have linux experience.  Do you understand how interrupts  
work in, say, a linux device driver, or on a legacy x86?

There's this general problem explaining things to people who have  
significant experience in some related area but nothing in the area in  
question.  If you word your answers too simply it comes across as  
insulting or isn't useful, but it's very easy to trip over a line into  
terms that just aren't part of the questioner's vocabulary (the whole  
"mil" thing being a fine example.)  In microcontrollers, this usually  
shows up when someone has a lot of electronics background but has  
never done software, or a lot of software background but has never  
done electronics.  I run into it frquently, trying to find books on  
windows programming for someone with a lot of experience in CLI and  
embedded software.

So in order to do something with interrupts in general, you need to:

1) Set up some code that is executed when the interrupt occurs (The  
"Interrupt Service Routine" or ISR)
2) configure the Interrupt Controller and/or interrupt vector table so  
that the desired interrupt or hardware signal will cause a jump/call  
to the ISR code.
3) configure the device that is supposed to generate the interrupt  
appropriately.
4) globally enable interrupts at the CPU level.

In your sample snippet of code, you did (3) without doing any of the  
other things.
It actually raised an interesting question for me (I've never used  
change pin interrupts): does IoC configured on a port cause the PIC to  
wake up from sleep even if higher levels of interrupt control aren't  
enabled?  It seems like it should, but then if it did I would think  
your code would work.

Some CPUs return to sleep mode when they're done executing the ISR, if  
they were in sleep mode when the interrupt occurred.  I don't recall  
whether the PIC is one of them.  Sometimes this is a consequence of  
sleep status being part of the "status register" that an interrupt  
saves automatically.  If so, part of the ISR has to be explicitly  
change the status register or sleep status before returning.

BillW

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