Argh !! Interrupt scratchpad variables !!

[mpfj]

I have seen this before, but I've never found a *real* solution to the problem.

I have a largish program using up 44% ROM and 63% RAM in a PIC18F8720, compiler 3v190.

In this code I use the RDA interrupt, which calls a function queue_in_irq() to queue any incoming serial characters.

I also have a function, display_show_bitmap() that displays a bitmap to an LCD. This can take a (relatively) long time, and it is quite possible for one (or more) RDA interrupts to occur while this display_show_bitmap() function is running.

My problem is that, as shown in my .SYM listing, the compiler has chosen to overlap it's queue_in_irq() SCRATCH variables with the variables and parameters used in display_show_bitmap().

I know I can define the local variables in display_show_bitmap() as STATIC to overcome this overlapping problem, but how do I prevent the compiler from overlapping the parameters ?

The code extract looks something like this ...

[ckielstra]

My guess is you are calling queue_in_irq() from both inside the interrupt and from within main()?
If yes, then this is what causes the memory overlap. Check the compiler manual in the chapter 'What are the restrictions on function calls from an interrupt function?'. According to this chapter the overlap shouldn't be a problem because the compiler adds instructions for disabling interrupts when entering the shared function. Disadvantage is that this causes additional interrupt latency.

A way around this is to create a diffent named copy of the shared function. Easier and more beautiful is using the #separate identifier, but I'm not sure this will work.

[mpfj]