Post by thread:[PIC]: how does this exit the ISR?

Here is a snippit of code, right out of AN734 ISR <deleted the save stuff for the ISR entry> banksel PIR1 btfss PIR1,SSPIF ; Is this a SSP interrupt? goto $ ; No, just trap here. bcf PIR1,SSPIF call SSP_Handler ; Yes, service SSP interrupt. <deleted the recall for saved stuff> retfie ; Return from interrupt. From this...it checks the PIR1 bit to see if the I2C is the source of interupt and if so, clears it and handles it. Otherwise the 'goto $' makes it just sit and stay there, so how does it exit the ISR if the interupt is not from the I2C, or given that there cannot be another source, does it simply lock up then? Not exactly sure what is going on there. _________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

as I started to think....perhaps its the WDT that forces it out? {Quote hidden}>From: Micro Eng <.....micro_engKILLspam@spam@HOTMAIL.COM> >Reply-To: pic microcontroller discussion list <PICLISTKILLspamMITVMA.MIT.EDU> >To: .....PICLISTKILLspam.....MITVMA.MIT.EDU >Subject: [PIC]: how does this exit the ISR? >Date: Thu, 21 Mar 2002 09:24:23 -0700 > >Here is a snippit of code, right out of AN734 > >ISR ><deleted the save stuff for the ISR entry> > > banksel PIR1 > btfss PIR1,SSPIF ; Is this a SSP interrupt? > goto $ ; No, just trap here. > bcf PIR1,SSPIF > call SSP_Handler ; Yes, service SSP interrupt. > ><deleted the recall for saved stuff> > > retfie ; Return from interrupt. > >From this...it checks the PIR1 bit to see if the I2C is the source of >interupt and if so, clears it and handles it. Otherwise the 'goto $' makes >it just sit and stay there, so how does it exit the ISR if the interupt is >not from the I2C, or given that there cannot be another source, does it >simply lock up then? Not exactly sure what is going on there. > >_________________________________________________________________ >Send and receive Hotmail on your mobile device: http://mobile.msn.com > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email EraseMElistservspam_OUTTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body > > _________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

>as I started to think....perhaps its the WDT that forces it out? ..... >Here is a snippit of code, right out of AN734 > >ISR ><deleted the save stuff for the ISR entry> > > banksel PIR1 > btfss PIR1,SSPIF ; Is this a SSP interrupt? > goto $ ; No, just trap here. > bcf PIR1,SSPIF > call SSP_Handler ; Yes, service SSP interrupt. The as published code would have a jump to somewhere else specified instead of the $ to handle some other interrupt, e.g. timer or uart, would be my expectation. I cannot see how they expect any use to be made of the transfer otherwise. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> Here is a snippit of code, right out of AN734 > > ISR > <deleted the save stuff for the ISR entry> > > banksel PIR1 > btfss PIR1,SSPIF ; Is this a SSP interrupt? > goto $ ; No, just trap here. > bcf PIR1,SSPIF > call SSP_Handler ; Yes, service SSP interrupt. > > <deleted the recall for saved stuff> > > retfie ; Return from interrupt. > > From this...it checks the PIR1 bit to see if the I2C is the source of > interupt and if so, clears it and handles it. Otherwise the 'goto $' makes > it just sit and stay there, so how does it exit the ISR if the interupt is > not from the I2C, It doesn't. > or given that there cannot be another source, does it > simply lock up then? Yes. > Not exactly sure what is going on there. You found a very poorly written example. In general I find the Microchip example code pretty poor. Reading the manual to understand how to do it yourself is much better than copying their stuff. I don't look at Microchip example code anymore. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, KILLspamolinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email RemoveMElistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

> banksel PIR1 > btfss PIR1,SSPIF ; Is this a SSP interrupt? > goto $ ; No, just trap here. > bcf PIR1,SSPIF > call SSP_Handler ; Yes, service SSP interrupt. > > >From this...it checks the PIR1 bit to see if the I2C is the source of > interupt and if so, clears it and handles it. Otherwise the 'goto $' makes > it just sit and stay there, so how does it exit the ISR if the interupt is > not from the I2C, or given that there cannot be another source, does it > simply lock up then? Not exactly sure what is going on there. Yes, it just locks up if not an I2C interrupt. This is an example, and they didn't have any other sources of interrupt, but put the stub there for you to use if you have other sources of interrupt, just change the jump. Cheerful regards, Bob -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spamBeGonelistservspamBeGonemitvma.mit.edu with SET PICList DIGEST in the body