Post by thread:PIC interrupts

Hi! How do I deal with interrupts in PIC16x.. ? Here's what I (think) know: - Single int vector in 0x0004 - I need to check which int to handle in the routine But, what flags are changed upon an interrupt call, and which flags are recovered after the int call? >From the docs, I think it's possible to use the ints in a polling way. I would do this by disabling the GIE (mask off all ints) and then, in the code, check the individual flags. Is this possible? Thank you, Nuno. -- .^. _,^,_ /\ ___( | )_____ Nuno Filipe Freitas Pedrosa __________ o(`} | , __/\/ /__ /*\\|//*\ SIEMENS S.A. Portugal (]| /' \ \/\ \(\\V//)/ spam_OUTNuno.PedrosaTakeThisOuToen.siemens.de (]|`% (") \/\ \ ` -=- ' Tel. :00351-1-4242454 (") /`/ / /\/ __B//|\\P___________________________________________\' / `/______\/____ `-' "Try and leave this world a little better than you found it..."

On Wed, Aug 26, 1998 at 11:02:13AM +0000, Nuno Pedrosa wrote: > Hi! How do I deal with interrupts in PIC16x.. ? > > - Single int vector in 0x0004 > - I need to check which int to handle in the routine Correct. Be aware that you must check both the flag and enable bits to determine if an interrupt actually was triggered by a particular source - the flag bits will be set even if the corresponding enable bit is not. > But, what flags are changed upon an interrupt call, and which flags are > recovered after the int call? None. If you do anything in your interrupt routine that may alter the flags, you must save them first. This means you can do things like bit test and set instructions, but not much else, without saving the status. To save the status you must first save W, and how and where you do that is dependent on the particular PICMicro, since some have RAM in all banks, some have common RAM, some have RAM in bank0 only but SFRs in bank1 etc. It's quite a job to cater for all that (a good C compiler does that for you, hint, hint!) > >From the docs, I think it's possible to use the ints in a polling way. > I would do this by disabling the GIE (mask off all ints) and then, in > the code, check the individual flags. Yup absolutely, if you call that using interrupts (which it ain't). But it's a perfectly legitimate technique for some situations. HAve fun! -- Clyde Smith-Stubbs | HI-TECH Software Email: .....clydeKILLspam@spam@htsoft.com | Phone Fax WWW: http://www.htsoft.com/ | USA: (408) 490 2885 (408) 490 2885 PGP: finger clydeKILLspamhtsoft.com | AUS: +61 7 3354 2411 +61 7 3354 2422 --------------------------------------------------------------------------- HI-TECH C: compiling the real world.

Hi, yes, it is possible to check the IT flags. However, you should reset the flags the same way as in the ISR. To answer the question which flags are re-set, see the following: all the IT's have their individual enable flags (maybe associated with any group or global flag), ending with E, e. g. INTE. then the IT will set the associated F flag (e. g. INTF). You must evaluate these, and reset that caused the interrupt actually. In the majority of cases, the E and F bits are in the same register. Not always, but more and more often ("nicht immer, aber immer šfter!"). Imre On Wed, 26 Aug 1998, Nuno Pedrosa wrote: {Quote hidden}> Hi! How do I deal with interrupts in PIC16x.. ? > > Here's what I (think) know: > - Single int vector in 0x0004 > - I need to check which int to handle in the routine > > But, what flags are changed upon an interrupt call, and which flags are > recovered after the int call? > > >From the docs, I think it's possible to use the ints in a polling way. > I would do this by disabling the GIE (mask off all ints) and then, in > the code, check the individual flags. > Is this possible? > > Thank you, > Nuno. > > -- > .^. _,^,_ /\ > ___( | )_____ Nuno Filipe Freitas Pedrosa __________ o(`} | , __/\/ /__ > /*\\|//*\ SIEMENS S.A. Portugal (]| /' \ \/\ > \(\\V//)/ .....Nuno.PedrosaKILLspam.....oen.siemens.de (]|`% (") \/\ \ > ` -=- ' Tel. :00351-1-4242454 (") /`/ / /\/ > __B//|\\P___________________________________________\' / `/______\/____ > `-' "Try and leave this world a little better than you found it..." > >

> Van: Nuno Pedrosa <EraseMEnuno.pedrosaspam_OUTTakeThisOuTOEN.SIEMENS.DE> > Aan: PICLISTspam_OUTMITVMA.MIT.EDU > Onderwerp: PIC interrupts > Datum: woensdag 26 augustus 1998 13:02 > > Hi! How do I deal with interrupts in PIC16x.. ? > > Here's what I (think) know: > - Single int vector in 0x0004 > - I need to check which int to handle in the routine Correct ! > But, what flags are changed upon an interrupt call, and which flags are > recovered after the int call? Aww ... In a PIC ? None & none ! You have to do it yourself offcourse ;-) > >From the docs, I think it's possible to use the ints in a polling way. > I would do this by disabling the GIE (mask off all ints) and then, in > the code, check the individual flags. > Is this possible? Yes. That's right. Greetz, Rudy Wieser

Hi Folks, > > But, what flags are changed upon an interrupt call, and which flags are > > recovered after the int call? I think this question is misunderstood. I think Pedro likes to know, what irq-flag is set if e.g. tmr0-irq appears, what flags ar reset/cleared with the retfie instructions. Pedro, have a look at the Data-sheet which will be a good source for answers. You have GIE which enables or disables interrupts at all. Also you have the interrupt-enable-flag's and corresponding interupt flag's. When GIE enables interupts and each special irq-enable-flag is set an jump to org 0004h is executed. The interupt flag's can be used to test which of the enabled interrupts occured. for further reading refer to the corresponding PIC-Data-sheet. ( I don4t like to give the info, and have no data-sheet available at th moment). Kind regards Stefan Sczekalla-Waldschmidt @spam@sswKILLspamoikossw.de

On Thu, 27 Aug 1998 15:59:04 +0100 Stefan Sczekalla-Waldschmidt <RemoveMEsswTakeThisOuTOIKOSSW.DE> writes: >Hi Folks, > >> > But, what flags are changed upon an interrupt call, and which >flags are >> > recovered after the int call? > >I think this question is misunderstood. > >I think Pedro likes to know, what irq-flag is set if e.g. >tmr0-irq appears, what flags ar reset/cleared with the retfie >instructions. The GIE flag is the only one that is automatically operated. It is always cleared when an interrupt starts (after the last instruction in the interrupted program executes, but before the first instruction in the ISR executes). This prevents the ISR from being interrupted. The RETFIE instruction sets GIE before returning. (The set of GIE is the only difference between RETFIE and RETURN.) If an interrupt is still pending when the RETFIE executes, the PIC will start again at the top of the ISR before executing any of the main program. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

The response below is correct, but there is one more matter of interest that must be taken into account. Before performing the RETFIE you must Clear the appropriate interrupt flag bit. Failure to do so will cause the interrupt to re-assert itself over and over again. The "appropriate" flag bit to Clear is the one associated with the interrupt action taken. In many programs the user may only have enabled a single form of interrupt, but often the user will enable multiple interrupt sources, and in that case the ISR (Interrupt Service Routine) must poll the interrupt flags, perform the appropriate action, and then Clear the appropriate interrupt flag just prior to executing the RETFIE instruction. Hope this helps. Fr. Tom McGahee ---------- {Quote hidden}> From: Mike Keitz <spamBeGonemkeitzspamBeGoneJUNO.COM> > To: TakeThisOuTPICLISTEraseMEspam_OUTMITVMA.MIT.EDU > Subject: Re: PIC interrupts > Date: Thursday, August 27, 1998 11:24 AM > > On Thu, 27 Aug 1998 15:59:04 +0100 Stefan Sczekalla-Waldschmidt > <RemoveMEsswTakeThisOuTOIKOSSW.DE> writes: > >Hi Folks, > > > >> > But, what flags are changed upon an interrupt call, and which > >flags are > >> > recovered after the int call? > > > >I think this question is misunderstood. > > > >I think Pedro likes to know, what irq-flag is set if e.g. > >tmr0-irq appears, what flags ar reset/cleared with the retfie > >instructions. > > The GIE flag is the only one that is automatically operated. It is > always cleared when an interrupt starts (after the last instruction in > the interrupted program executes, but before the first instruction in the > ISR executes). This prevents the ISR from being interrupted. The RETFIE > instruction sets GIE before returning. (The set of GIE is the only > difference between RETFIE and RETURN.) If an interrupt is still pending > when the RETFIE executes, the PIC will start again at the top of the ISR > before executing any of the main program. > > > _____________________________________________________________________ > You don't need to buy Internet access to use free Internet e-mail. > Get completely free e-mail from Juno at http://www.juno.com > Or call Juno at (800) 654-JUNO [654-5866]

Hi! Thank you all for your help! Int handling is quite simple to understand in PIC, I guess. PIC does very little. 8) I know what I wanted: on a int, the GIE is disabled, and then will be enabled by RETFIE. All other flags, all the registers and whatever cleaning is needed, must be done in SW. Regarding Stack Manipulation, someone suggested me to use C. 8) Well, I'd love to, but the PIC needs to complete certain tasks in less than 64us in my project. So, since they are simple, I stood by assembly. It's not that difficult...I just comment each line, so I don't forget what it does. ;) Have a nice weekend! Nuno Pedrosa. {Quote hidden}> The response below is correct, but there is one more matter > of interest that must be taken into account. Before performing > the RETFIE you must Clear the appropriate interrupt flag bit. > Failure to do so will cause the interrupt to re-assert itself > over and over again. The "appropriate" flag bit to Clear is > the one associated with the interrupt action taken. In many > programs the user may only have enabled a single form of > interrupt, but often the user will enable multiple interrupt > sources, and in that case the ISR (Interrupt Service Routine) > must poll the interrupt flags, perform the appropriate action, > and then Clear the appropriate interrupt flag just prior to > executing the RETFIE instruction. > > >I think this question is misunderstood. > > > > > >I think Pedro likes to know, what irq-flag is set if e.g. > > >tmr0-irq appears, what flags ar reset/cleared with the retfie > > >instructions. > > > > The GIE flag is the only one that is automatically operated. It is > > always cleared when an interrupt starts (after the last instruction in > > the interrupted program executes, but before the first instruction in the > > ISR executes). This prevents the ISR from being interrupted. The RETFIE > > instruction sets GIE before returning. (The set of GIE is the only > > difference between RETFIE and RETURN.) If an interrupt is still pending > > when the RETFIE executes, the PIC will start again at the top of the ISR > > before executing any of the main program. -- .^. _,^,_ /\ ___( | )_____ Nuno Filipe Freitas Pedrosa __________ o(`} | , __/\/ /__ /*\\|//*\ SIEMENS S.A. Portugal (]| /' \ \/\ \(\\V//)/ Nuno.PedrosaEraseME.....oen.siemens.de (]|`% (") \/\ \ ` -=- ' Tel. :00351-1-4242454 (") /`/ / /\/ __B//|\\P___________________________________________\' / `/______\/____ `-' "Try and leave this world a little better than you found it..."