Post by thread:[PIC] Interrupt Questions

I really have not had too much experience with interrupts, i have built and coded a few things that should have had them, mostly for the reason that way back when i first started learning about PICs, i was always warned how hard interrupts where to implement and that i should find a way to work without them. so that turned me off from them for the longest time. but i know they have there place and i need to start using them more. So 1. if i am using RB0/INT as my interrupt source, can i still read RB0 as a bit without disabling interrupts? ie. waiting for input to fall back down. also can i exit a interrupt routine with a "goto" instead of a "retfie"? ie. if i need to stop the program from what its doing and do something completely different. -- View this message in context: www.nabble.com/Interrupt-Questions-tp18697286p18697286.html Sent from the PIC - [PIC] mailing list archive at Nabble.com.

Hi Three, You can still read the pin even if it's set up to be an interrupt. As far as using a goto instead of a retfie, any path you take must eventually end in retfie or you'll break the stack. And since you ask the question, let me suggest that by asking that particular question I think the structure of your program is faulty if you are thinking about doing it that way. Interrupts should be fairly short, maybe increment a counter, put a byte in a buffer, or set a flag and then return. Cheerful regards, Bob On Mon, 28 Jul 2008 12:07:40 -0700 (PDT), "threewheeler7" <spam_OUTthreewheeler7TakeThisOuThotmail.com> said: {Quote hidden}> > I really have not had too much experience with interrupts, i have built > and > coded a few things that should have had them, mostly for the reason that > way > back when i first started learning about PICs, i was always warned how > hard > interrupts where to implement and that i should find a way to work > without > them. so that turned me off from them for the longest time. but i know > they > have there place and i need to start using them more. So 1. if i am using > RB0/INT as my interrupt source, can i still read RB0 as a bit without > disabling interrupts? ie. waiting for input to fall back down. also can i > exit a interrupt routine with a "goto" instead of a "retfie"? ie. if i > need > to stop the program from what its doing and do something completely > different. -- http://www.fastmail.fm - IMAP accessible web-mail

----- Original Message ----- From: "threewheeler7" <.....threewheeler7KILLspam@spam@hotmail.com> To: <piclistKILLspammit.edu> Sent: Monday, July 28, 2008 3:07 PM Subject: [PIC] Interrupt Questions > > I really have not had too much experience with interrupts, i have built > and > coded a few things that should have had them, mostly for the reason that > way > back when i first started learning about PICs, i was always warned how > hard > interrupts where to implement and that i should find a way to work without > them. Not necessarily difficult, it just means a little bit of studying about what they are, how they work, and how to implement them. If you were "always" warned about how difficult they are to implement, you were being done an disservice. They definitely have their place in programming any microprocessor or microcontroller. In fact, I dare say, you can 't get along without them if you are going to do any serious, or even semi-serious, programming. > so that turned me off from them for the longest time. but i know they > have there place and i need to start using them more. So 1. if i am using > RB0/INT as my interrupt source, can i still read RB0 as a bit without > disabling interrupts? ie. waiting for input to fall back down. Once enabled as an interrupt, what purpose would be served by reading the pin? A change of state on RB0 will initiate an interrupt - what you decide to do with that information is up to you. You can ignore it or you can use that information to do something. If you want to use RB0 for some other purpose (as a general purpose I/O pin), you should disable the interrupt. > also can i > exit a interrupt routine with a "goto" instead of a "retfie"? ie. if i > need > to stop the program from what its doing and do something completely > different. I supose you could but, if you think you need to, you likely don't really want to use an interrupt to accomplish whatever it is you are trying to do. You don't have an unlimited stack, so how are you going to handle stack overflow after the number of times you get an interrupt exceeds stack size? How are you going to re-enable the interrupt? How are you going to handle situations where you 'interrupted' a routine that produces an change to an output that you need to know the result of, if you don't return to the point it was interrupted? Please take a look at the datasheet for your PIC; it probably contains some discussion about the RB0 interrupt. If you are using a mid-range PIC, the mid-range family reference (available on the Microchip site) gives a bit more info. I also recommend you try a Google search for the words PIC tutorial; many of the hits you will get cover interrupts in general, and the RB0 interrupt in particular. Some are better than others but, as you learn and experiment, you'll be able to spot the not-so-good ones. Good luck and have fun learning. Richard

>1. if i am using RB0/INT as my interrupt source, can i still read RB0 > as a bit without disabling interrupts? ie. waiting for input to fall back > down Yes. You can also change the edge which triggers the interrupt. ie you can select to detect when the pin goes L->H and/or when it goes H->L > also can i exit a interrupt routine with a "goto" instead of a "retfie"? Yes, but there will be a return address left on the stack, and each time that ISR is called. Eventually there'll be a crash. PICs with POP can deal with orphaned addresses on the stack if necessary, but you're better to exit with RETFIE to keep the stack tidy > ie.if i need to stop the program from what its doing and do something > completely different Not quite sure what you mean by that. When program flow enters an ISR, interrupts are turned off by the hardware. If you exit that ISR with RETURN instead of RETFIE, interrupts will not be turned back on

>> also can i exit a interrupt routine with a "goto" instead >> of a "retfie"? > Yes, but there will be a return address left on the stack, > and each time > that ISR is called. Eventually there'll be a crash. PICs > with POP can > deal with orphaned addresses on the stack if necessary, > but you're > better to exit with RETFIE to keep the stack tidy Translation: NO! You can't do this unless you are an expert and understand exactly what you are doing and what happens when you do it. Until then, just don't do it. The consequences will almost always be fatal (to the program's function if not to you). Russell