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Manfred1
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| How to reduce the stack |
 Posted: Thu Feb 04, 2010 6:43 am |
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Hello,
In the FAQ of the CCSINFO Page I have seen that the size of the stack should not exceed 9 if using interrupts.
| Quote: | "What are the restrictions on function calls from an interrupt function?
Whenever interrupts are used, the programmer MUST ensure there will be enough stack space. Ensure the size of the stack required by the interrupt plus the size of the stack already used by main() wherever interrupts are enabled is less than 9. This can be seen at the top of the list file. "
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if I look in my list file it says "Stack: 11 worst case (4 in main + 7 for interrupts)", so it seems as if I could get some unexpected problems. Further more, if I look in the list file of my bootloader it says "Stack: 4 locations"
Dose this mean that I have up to 15 (11 + 4) in the worst case?
How can I reduce the usage of the stack and is there a possibility to clear the stack after the bootloader jumps to the main program, as I suppose this stack information is not needed any more in the main program and would save the 4.
I am using ccs 4.103 and a PIC18F6722. |
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Ttelmah
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| Posted: Thu Feb 04, 2010 9:53 am |
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It sounds as if this is a 'FAQ' answer, for a much older chip.
The limit on stack size, is dependant on the processor.
Most of the chips used in the earlier CCS versions, were limited at 8 stack levels (<9)....
Many modern chips allow far more entries (your chip allows 31 levels), and several of the CCS demo programs use more than 9 levels - with interrupts.
There is a balancing act here. You will use the stack,whenever you call a subroutine, which is of reasonable size, and called from multiple points in the code. This costs speed slightly. You can force the code to instead be put 'inline', (by using the inline directive), this gives faster performance, and avoids using the stack, but at a cost in ROM useage.
However, at 11 entries, don't bother. Worry about it if you get up to perhaps 25 levels.
Best Wishes |
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