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KenMacfarlane
Joined: 20 Sep 2005
Posts: 23
Location: Glasgow, Scotland, UK
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| How to pass non-constant args to to input(PIN_B0)) |
 Posted: Tue Mar 07, 2006 8:27 am |
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I wish I could parameterise code like that below, then I wouldn't have to hardcode it for each bit that I want to test. Is there any way around a func that insists on a constant for an arg?
| Code: |
b5_went_low = FALSE;
while ( !b5_went_low ) // N.B. you have to press SW2 to get out of the loop
{
while( input(PIN_B0)) // if only I could pass arg - const only means having to hardcode it
;
sprintf(pszTmp, "Open ");
LCD_putstr_xy(pszTmp, LCD_COL0+6, LCD_ROW1);
//delay_ms(TEST_HOLD_TIME);
while( !input(PIN_B0))
;
sprintf(pszTmp, "Shorted");
LCD_putstr_xy(pszTmp, LCD_COL0+6, LCD_ROW1);
//delay_ms(TEST_HOLD_TIME);
}
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I would have thought that it was not significantly more difficult for a compiler to compile a call that pushes a variable address on the stack than a constant...? |
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Ttelmah
Guest
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| Posted: Tue Mar 07, 2006 9:48 am |
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The compiler does not call a routine,and push a constant onto the stack. The PIC, does not have a stack for variables (only for addresses). The constant code, does not generate a routine at all, but just uses the processor 'bit set' function, which only accepts a constant.
The 'variable' version, will be a lot bulkier (typically about 30 to 40* the size of the constant access), but may well be worthwhile.
The common way of doing this, is to address the port through a pointer, and then use a bit mask. If you only need to access different bits in a single port, then the overhead is a lot less. There have been dozens of routines published here in the past to do this, and a search ought to find these.
Best Wishes |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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