Interrupts.... - Electronic Circuits Projects Diagrams Free

asp1987 · 1st October 2007, 05:50 AM

Suppose an interrupt occurs and a table is called initially in the ISR..The
table directs the micro to do an appropriate action defined within the ISR itself..
During its execuiton we have cleared both RBIF and INTF flags to allow more interrupts.. Now suppose we are still in the ISR(doing that 'appropriate' action)..

1.Will another interrupt cause the PC to direct at the table?
2.Or is it necessary that our program has to be out of the ISR(using retfie) to enable further interrupts?
Thanks in advance...

Pommie · 1st October 2007, 06:37 AM

The GIE bit is cleared when an ISR is entered and is set when the retfie is executed. This makes it impossible for another interrupt to happen. You can allow re-entrant interrupts by setting the GIE bit in your ISR but you have to copy the w_temp variables etc into shadow locations first.

BTW, this assumes 16F series chip.

Mike.

Sceadwian · 1st October 2007, 06:58 AM

You have to be careful with that, nested interupts can get out of control fast and cause stack overflows.

**Nigel Goodwin** · 1st October 2007, 09:11 AM

I would strongly suggest NOT doing it!.

It's also fairly important to make ISR's as short and fast as possible, and preferably NOT to call subroutines within them - as the limited stack size means it's easy to overflow the stack, with disasterous results.

asp1987 · 1st October 2007, 12:33 PM

Thanks a lot.....

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1st October 2007, 05:50 AM	(permalink)
asp1987	Interrupts.... Suppose an interrupt occurs and a table is called initially in the ISR..The table directs the micro to do an appropriate action defined within the ISR itself.. During its execuiton we have cleared both RBIF and INTF flags to allow more interrupts.. Now suppose we are still in the ISR(doing that 'appropriate' action).. 1.Will another interrupt cause the PC to direct at the table? 2.Or is it necessary that our program has to be out of the ISR(using retfie) to enable further interrupts? Thanks in advance...

1st October 2007, 06:37 AM	(permalink)
Pommie	The GIE bit is cleared when an ISR is entered and is set when the retfie is executed. This makes it impossible for another interrupt to happen. You can allow re-entrant interrupts by setting the GIE bit in your ISR but you have to copy the w_temp variables etc into shadow locations first. BTW, this assumes 16F series chip. Mike.

1st October 2007, 06:58 AM	(permalink)
Sceadwian	You have to be careful with that, nested interupts can get out of control fast and cause stack overflows. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

1st October 2007, 09:11 AM	(permalink)
Nigel Goodwin	I would strongly suggest NOT doing it!. It's also fairly important to make ISR's as short and fast as possible, and preferably NOT to call subroutines within them - as the limited stack size means it's easy to overflow the stack, with disasterous results. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

1st October 2007, 12:33 PM	(permalink)
asp1987	Thanks a lot.....