[sdcc-devel] [ sdcc-Bugs-1577882 ] Partial BANKSEL for PORTA assignment at while(1) loop start

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Bugs item #1577882, was opened at 2006-10-15 21:33
Message generated for change (Comment added) made by mcody
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Mac Cody (mcody)
Assigned to: Nobody/Anonymous (nobody)
Summary: Partial BANKSEL for PORTA assignment at while(1) loop start

Initial Comment:
This problems appears to be related to bug report
1570934.  Testing was performed on a PIC16F628 using
Slackware Linux 10.2 (kernel 2.4.31).  The compiler is
SDCC 2.6.1 #4409 (Oct 15 2006) (UNIX).  The command
line for the compile is

sdcc -debug -mpic14 -p16f628 SDCC_Test2.c

The problem appears to occur when a PORTA assignment
occurs at the beginning of a while(1) loop (i.e.
endless).  The first C code examples compiles and yelds
the expected results on the 16F628 (the LED connected
to PORTA0 flashes.  Note that the PORTA assignment
follows the assignment of the variable count1.  The
compiled assembly follows.  Note that the bcf command
is used to clear both bits 5 and 6 of the STATUS register.

The second C code example has the PORTA assignment
immediately following the head of the while(1) loop.
While the code compiles, the code running on the
PIC16F628 only flashes once.  Note that the bcf command
is used to only clear bit 5.  Bit 6 is cleared as part
of the TRISA code outside of the while(1) loop.  The
TRISA code at the beginning of the program causes
PORTA0 pin to become an output and the PORTA0 bit is
already 0 due to system reset.  This causes the LED to
light.  Latter on in the program, PORTA0 is set to 1,
which turns the LED off.  It appears that the BANKSEL
associated with second "count--" performs a bsf for
STATUS bit 6, which is not cleared when the branch goes
back to the beginning of the while loop.

I don't have a patch to fix the problem, but I think I
tracked down the cause of the problem.

**** START FIRST C CODE EXAMPLE ****
#define __16f628
#include "pic/pic16f628.h"

// Set the __CONFIG word:
typedef unsigned int word;
word at 0x2007  __CONFIG = 0x3D90;

#pragma nogcse
void main(void) {
	unsigned short count1;

        TRISA = 0;
	while(1) {
                count1 = 0x7fff;
		PORTA = 0;
		while(count1 != 0) {
			count1--;
		}
		PORTA = 1;
		count1 = 0x7fff;
		while(count1 != 0) {
			count1--;
		}
	}
}
**** END FIRST C CODE EXAMPLE ****
**** START FIRST ASSEMBLY CODE EXAMPLE ****
**** NOTE: LEADING ASSEMBLY DEFINITIONS LEFT OFF ****

_main	;Function start
; 2 exit points
;	.line	12; "SDCC_Test2.c"	TRISA = 0;
	BSF	STATUS,5
	BCF	STATUS,6
	CLRF	_TRISA
_00112_DS_
;	.line	14; "SDCC_Test2.c"	count1 = 0x7fff;
	MOVLW	0xff
	BANKSEL	r0x1002
	MOVWF	r0x1002
	BANKSEL	r0x1000
	MOVWF	r0x1000
	MOVLW	0x7f
	BANKSEL	r0x1003
	MOVWF	r0x1003
	BANKSEL	r0x1001
	MOVWF	r0x1001
;	.line	15; "SDCC_Test2.c"	PORTA = 0;
	BCF	STATUS,5    <== Bit 5 cleared
	BCF	STATUS,6    <== Bit 6 cleared
	CLRF	_PORTA
;;99	MOVF	r0x1000,W
;;100	MOVF	r0x1001,W
_00105_DS_
;	.line	16; "SDCC_Test2.c"	while(count1 != 0) {
	BANKSEL	r0x1002
	MOVF	r0x1002,W
;;     peep 1 - test/jump to test/skip
;	.line	17; "SDCC_Test2.c"	count1--;
	BANKSEL	r0x1003
	IORWF	r0x1003,W
	BTFSC	STATUS,2
	GOTO	_00107_DS_
	MOVLW	0xff
	BANKSEL	r0x1002
	ADDWF	r0x1002,F
	BTFSC	STATUS,0
	GOTO	_00001_DS_
	BANKSEL	r0x1003
	DECF	r0x1003,F
_00001_DS_
	GOTO	_00105_DS_
_00107_DS_
;	.line	19; "SDCC_Test2.c"	PORTA = 1;
	MOVLW	0x01
	BCF	STATUS,5
	BCF	STATUS,6
	MOVWF	_PORTA
;	.line	20; "SDCC_Test2.c"	count1 = 0x7fff;
	MOVLW	0xff
	BANKSEL	r0x1000
	MOVWF	r0x1000
	MOVLW	0x7f
	BANKSEL	r0x1001
	MOVWF	r0x1001
_00108_DS_
;	.line	21; "SDCC_Test2.c"	while(count1 != 0) {
	BANKSEL	r0x1000
	MOVF	r0x1000,W
;;     peep 1 - test/jump to test/skip
;	.line	22; "SDCC_Test2.c"	count1--;
	BANKSEL	r0x1001
	IORWF	r0x1001,W
	BTFSC	STATUS,2
	GOTO	_00112_DS_
	MOVLW	0xff
	BANKSEL	r0x1000
	ADDWF	r0x1000,F
	BTFSC	STATUS,0
	GOTO	_00002_DS_
	BANKSEL	r0x1001
	DECF	r0x1001,F
_00002_DS_
	GOTO	_00108_DS_
	RETURN	
; exit point of _main


;	code size estimation:
;	   41+   14 =    55 instructions (  138 byte)

	end
**** END FIRST ASSEMBLY CODE EXAMPLE ****
**** START SECOND C CODE EXAMPLE ****
#include "pic/pic16f628.h"

// Set the __CONFIG word:
typedef unsigned int word;
word at 0x2007  __CONFIG = 0x3D90;

#pragma nogcse
void main(void) {
	unsigned short count1;

        TRISA = 0;
	while(1) {
		PORTA = 0;
                count1 = 0x7fff;
		while(count1 != 0) {
			count1--;
		}
		PORTA = 1;
		count1 = 0x7fff;
		while(count1 != 0) {
			count1--;
		}
	}
}
**** END SECOND C CODE EXAMPLE ****
**** START SECOND ASSEMBLY CODE EXAMPLE ****
**** NOTE: LEADING ASSEMBLY DEFINITIONS LEFT OFF ****

_main	;Function start
; 2 exit points
;	.line	12; "SDCC_Test2.c"	TRISA = 0;
	BSF	STATUS,5
	BCF	STATUS,6
	CLRF	_TRISA
_00112_DS_
;	.line	14; "SDCC_Test2.c"	PORTA = 0;
	BCF	STATUS,5    <== Only bit 5 cleared
	CLRF	_PORTA
;	.line	15; "SDCC_Test2.c"	count1 = 0x7fff;
	MOVLW	0xff
	BANKSEL	r0x1002
	MOVWF	r0x1002
	BANKSEL	r0x1000
	MOVWF	r0x1000
	MOVLW	0x7f
	BANKSEL	r0x1003
	MOVWF	r0x1003
	BANKSEL	r0x1001
	MOVWF	r0x1001
;;99	MOVF	r0x1000,W
;;100	MOVF	r0x1001,W
_00105_DS_
;	.line	16; "SDCC_Test2.c"	while(count1 != 0) {
	BANKSEL	r0x1002
	MOVF	r0x1002,W
;;     peep 1 - test/jump to test/skip
;	.line	17; "SDCC_Test2.c"	count1--;
	BANKSEL	r0x1003
	IORWF	r0x1003,W
	BTFSC	STATUS,2
	GOTO	_00107_DS_
	MOVLW	0xff
	BANKSEL	r0x1002
	ADDWF	r0x1002,F
	BTFSC	STATUS,0
	GOTO	_00001_DS_
	BANKSEL	r0x1003
	DECF	r0x1003,F
_00001_DS_
	GOTO	_00105_DS_
_00107_DS_
;	.line	19; "SDCC_Test2.c"	PORTA = 1;
	MOVLW	0x01
	BCF	STATUS,5
	BCF	STATUS,6
	MOVWF	_PORTA
;	.line	20; "SDCC_Test2.c"	count1 = 0x7fff;
	MOVLW	0xff
	BANKSEL	r0x1000
	MOVWF	r0x1000
	MOVLW	0x7f
	BANKSEL	r0x1001
	MOVWF	r0x1001
_00108_DS_
;	.line	21; "SDCC_Test2.c"	while(count1 != 0) {
	BANKSEL	r0x1000
	MOVF	r0x1000,W
;;     peep 1 - test/jump to test/skip
;	.line	22; "SDCC_Test2.c"	count1--;
	BANKSEL	r0x1001
	IORWF	r0x1001,W
	BTFSC	STATUS,2
	GOTO	_00112_DS_
	MOVLW	0xff
	BANKSEL	r0x1000 <== bcf STATUS,5; bsf STATUS,6
	ADDWF	r0x1000,F
	BTFSC	STATUS,0
	GOTO	_00002_DS_
	BANKSEL	r0x1001
	DECF	r0x1001,F
_00002_DS_
	GOTO	_00108_DS_
	RETURN	
; exit point of _main


;	code size estimation:
;	   40+   14 =    54 instructions (  136 byte)

	end
**** END SECOND ASSEMBLY CODE EXAMPLE ****



----------------------------------------------------------------------

>Comment By: Mac Cody (mcody)
Date: 2006-10-15 21:41

Message:
Logged In: YES 
user_id=497809

Note: I labeled the wrong BANKSEL on the second assembly
example.  It should be the line "BANKSEL r0x1001" three
lines prior to "GOTO _00112_DS".

----------------------------------------------------------------------

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