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kuwa
Guest
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| Using "FAST" Interrupt on PIC18 |
 Posted: Sun Aug 13, 2006 7:19 am |
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When FAST keyward are used in #int_xxx, compiler outputs highpriority
interrupt code without saving registers.
The interrupt code is as follows.
| Code: | 0008: MOVLB 0
000A: GOTO 0138
.................... #int_timer2 FAST
.................... void isr_timer2(void) {
.................... #ASM
.................... MOVFF 0xFE0,07
0138: MOVFF FE0,07
.................... #ENDASM
.................... }
013C: BCF F9E.1
013E: RETFIE 1 |
At 0008, code is always MOVLB 0.
It may overwrite 0 to BSR whichi is using in main program.
It will make trouble.
Why the compiler output such code?
How should I do to stop outputting the code, "MOVLB 0"? |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Sun Aug 13, 2006 7:40 am |
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| Read the datasheet on the PIC. Certain registers are saved by the PIC hardware. |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Sun Aug 13, 2006 8:53 am |
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The MOVLB instruction was added in v3.228 (or v3.227) to fix a bug where a C coded interrupt was assuming to be in bank zero by default. Placing the MOVLB instruction at the interrupt vector address is a quick-and-dirty fix. It works but in programs like yours where you don't access any C variables it adds an unwanted 1 instruction overhead.
Just curious, what do you have located at adres 0x0007? If this is a C variable that you dind't fix at this location with a #locate instruction, then the CCS generated code is actually just what you need.
More information on the bug fix: http://www.ccsinfo.com/forum/viewtopic.php?t=24950 |
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kuwa
Guest
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| Thanks! |
| Posted: Mon Aug 14, 2006 8:37 pm |
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>Mark
Oh! I had overlooked "Fast Regester Stack".
I should have noticed it,"RETFIE 1".
So, I understand no trouble will be.
Thank you. |
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kuwa
Guest
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| Thank you |
| Posted: Mon Aug 14, 2006 8:54 pm |
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>ckielstra
Thank you for the explanation about the history.
And,it"s a interest Idea.
So,I tried it.
But, if I write follows,
| Code: | #device HIGH_INTS=TRUE
#build (interrupt=0x07) |
interrupts start at 0x07 and 0x17.
So I thought, and made as follows.
| Code: | #device HIGH_INTS=TRUE
#build (interrupt=0x20)
#org 0x008,0x017
int_high_ent()
{
#asm
**** own code
BCF 0x***.*
RETFIE 1
#endasm
}
#org 0x018,0x01f
int_low_ent()
{
#asm
goto 0x30 // priority low entry
#endasm
} |
I am able to want to do.
But,,, I know It's needless thing. 
Thank you very much. |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Tue Aug 15, 2006 6:56 am |
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| The hardware will still jump to 0x08 and 0x18 and thus the 2 instructions at 0x07 and 0x17 will not get executed and thus not adding to the overhead. |
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kuwa
Guest
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| 0x0016 |
| Posted: Tue Aug 15, 2006 6:43 pm |
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But, "MOVLB 0" for low priority interrupt is not 0x0016, as follows.
| Code: | #build(interrupt=0x07)
0006: MOVLB 0
0008: GOTO 00AE
000C: NOP
000E: NOP
0010: NOP
0012: NOP
0014: NOP
0016: MOVFF FE8,05
001A: MOVFF FD8,06
001E: MOVFF FE0,07
0022: MOVLB 0
0024: MOVFF FE9,0D
0028: MOVFF FEA,08
002C: MOVFF FE1,09
.
. |
So, It may have trouble, if it jump to 0x17(exactly 0x16).
Thank you. |
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