[sdcc-devel] [ sdcc-Bugs-3160409 ] PIC16: subroutine call wrong?

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Bugs item #3160409, was opened at 2011-01-18 02:09
Message generated for change (Comment added) made by diegoherranz
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Category: pic16 target
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Herbert Pötzl (hpoetzl)
Assigned to: Nobody/Anonymous (nobody)
Summary: PIC16: subroutine call wrong?

Initial Comment:
basically loop for (val=0; val<16; val++) and output to pin (led) like this:
PORTC = val + 2; results in blinking led (on RC0) while
PORTC = add2(val) ; results in dark led

NOTE: this time the add2 seems to result in correct code, but for
 some reason add2(val) returns 0,2,4,6,8 ...

SPECULATION: the subroutine call gets the stack frame wrong so
it ends up adding to the previous result somehow?

compiled with --use-non-free -mpic16 -p18f26j50

--- bug02_good.asm	2011-01-18 02:07:28.000000000 +0100
+++ bug02_bad.asm	2011-01-18 02:07:44.000000000 +0100
@@ -472,10 +472,12 @@ _00117_DS_:
 	MOVLW	0x10
 	SUBWF	r0x00, W
 	BC	_00121_DS_
-;	.line	39; bug02.c	PORTC = val + 2;
-	MOVLW	0x02
-	ADDWF	r0x00, W
+;	.line	41; bug02.c	PORTC = add2(val);
+	MOVF	r0x00, W
+	MOVWF	POSTDEC1
+	CALL	_add2
 	MOVWF	_PORTC
+	INCF	FSR1L, F
 ;	.line	43; bug02.c	for (i=0; i<250; i++)
 	CLRF	r0x01

_add2:
;	.line	25; bug02.c	unsigned char add2(unsigned char val) {
	MOVFF	FSR2L, POSTDEC1
	MOVFF	FSR1L, FSR2L
	MOVFF	r0x00, POSTDEC1
	MOVLW	0x02
	MOVFF	PLUSW2, r0x00
;	.line	26; bug02.c	return val + 2;
	INCF	r0x00, F
	INCF	r0x00, F
	MOVF	r0x00, W
	MOVFF	PREINC1, r0x00
	MOVFF	PREINC1, FSR2L
	RETURN	


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Comment By: Diego Herranz (diegoherranz)
Date: 2011-09-17 18:35

Message:
Tried with sdcc --use-non-free -mpic16 -p18f2550 bug02.c (18f2550 instead
of 18f26j50 because I have simulator for 18f2550) and works with PORTC =
val + 2 and also with PORTC = add2(val). Both make RC0 blink.

My version is 3.0.0, which one are you using?
Can you test with another processors and tell us what happens?







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Comment By: Diego Herranz (diegoherranz)
Date: 2011-09-17 18:03

Message:
I think that I misunderstood your explanation and LATx/PORTx is not the
problem.
Anyway, I think that is a good practice to write always to LATx instead of
PORTx.

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Comment By: Diego Herranz (diegoherranz)
Date: 2011-09-17 17:55

Message:
Can you try to use LATC instead of PORTC?
PORTC reads the actual value (voltage) on the pin and due to capacitance,
changes are not made instantly. 
LATC is a latch register so you can know what should be on the port even
if actual voltage hasn't changed yet.

Please let us know if you try this.

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https://sourceforge.net/tracker/?func=detail&atid=100599&aid=3160409&group_id=599