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mpfj
Joined: 09 Sep 2003 Posts: 95 Location: UK
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Argh !! Interrupt scratchpad variables !! |
Posted: Tue Mar 15, 2005 9:57 am |
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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 ...
Code: | int1 queue_in_irq(queue_struct *q, char c) {
// ... code removed ...
}
#int_rda
void rx_irq_com1(void) {
int8 rx_char;
int1 got_rx_data = false;
// store rx data (and clear irq at the same time)
rx_char = RCREG1;
// ... parity checking removed ...
// if valid char, add to rx queue
if (got_rx_data) {
queue_in_irq(&serial.com1.qrx, rx_char);
}
}
void display_show_bitmap(int32 addr, int8 x, int8 y, int8 width, int8 height) {
int16 gfx_addr = GRAPHICS_BASE;
// ... code removed ...
}
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The .SYM listing shows ...
Code: | 959-95C display_show_bitmap.addr
95A keyboard_scan_irq.scan_in_value
95B keyboard_scan_irq.i
95C keyboard_scan_irq.j
95D display_show_bitmap.x
95D keyboard_scan_irq.key_value
95E display_show_bitmap.y
95E.0 keyboard_scan_irq.key_found
95F beeper_start.timeout
95F-960 queue_in_irq.q
95F display_show_bitmap.width
95F keyboard_scan_irq.@SCRATCH
960 digio_set_status_bit.i
960 display_show_bitmap.height
960 keyboard_scan_irq.@SCRATCH
961 queue_in_irq.c
961 digio_write_status.data
961-962 display_show_bitmap.gfx_addr
961 keyboard_scan_irq.@SCRATCH
962 keyboard_scan_irq.@SCRATCH
962 queue_in_irq.@SCRATCH
963-964 lcd_set_ptr.addr
963 multiply8x8.x
963 display_show_bitmap.@SCRATCH
963 queue_in_irq.@SCRATCH
964 multiply8x8.y
964 display_show_bitmap.@SCRATCH
964 queue_in_irq.@SCRATCH
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As you can see several of my "_irq" routines share ram locations with other functions.
How can I define the locations of the @SCRATCH variables such that they don't overlap ? |
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ckielstra
Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands
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Posted: Tue Mar 15, 2005 11:09 am |
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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. |
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mpfj
Joined: 09 Sep 2003 Posts: 95 Location: UK
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Posted: Tue Mar 15, 2005 2:37 pm |
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ckielstra wrote: | My guess is you are calling queue_in_irq() from both inside the interrupt and from within main()? |
Argh, argh and more argh ...
All this time I've been looking at an old copy of the .SYM file ...
As you correctly pointed out, I *do* call the display_show_bitmap() from both inside and outside the ISR. This is now fixed.
Sorry for wasting everyone's time. |
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