Instant Interrupts - Revisited

[sougata]

Hi,

I need to call a subroutine from within a low priority PBP instant interrupt on a PIC 18F452. I am using both High Priority and Low Priority Interrupts.

I need to know whether PBP uses a software stack for its gosub calls or use the PIC18 stack pointer. I am concerned if calling a nested gosub from within a PBP InstInt would cause stack overflow.

[Darrel Taylor]

PBP uses the hardware Stack. But with 31 levels on the 18F's, you have to be pretty sloppy to overflow it.

The PIC itself uses the Hardware Stack to handle an interrupt. But, DT_INTS does NOT use the Hardware Stack. It essentially uses a 2-level software stack. 1 for High Priority, and 1 for Low.

Once in an interrupt, it's OK to call a subroutine, as long as both HIGH and LOW priorities can never call the same routine at the same time.

HTH,

[sougata]

Dear Darrel,

Thank you for the reply. I am using ASM interrupts on your system for the the high priority and your system already uses the shadow register for HP (retfie fast).

My main routine has deep calls and in the low priority interrupts I am using PBP. I was actually overflowing the stack causing a MCU reset (configured for reset under STACK Over/underflow). I have re-structured my code to handle it already.

I must thank you once again for the great job you have done. It is not only about using PBP in Interrupts it is more manageable than asm.