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pin writes optimized out

I am pretty new to this stuff, but I am usually able to work out problems on my own. I am trying to interface to some humidity sensor that uses it's own proprietary 2-wire serial interface (clock line and a data line). To make things easier, I declared sbits for each pin (SCK and DATA). When I try to compile and execute code like this:

.
.
DATA = 1;
SCK = 1;
error = DATA;
SCK = 0;
.
.

the compiler omits the line "SCK = 1". This is just an example, and it happens sporadically throughout the code. I read on some other posts that sbits are automatically volatile, and similar rumors, but the compiler is optimizing necessary lines out anyway. My compiler version is 6.20a. Thanks

Parents

0 Jon Ward over 21 years ago in reply to Sean Warden

When I compiled your example, I got the following:

ASSEMBLY LISTING OF GENERATED OBJECT CODE


             ; FUNCTION L?0006 (BEGIN)
0000 C2C8              CLR     SCK
0002 120000      R     LCALL   Hold
0005 D2C8              SETB    SCK

; The above executes
;   SCK = 0;
;   Hold ();
;   SCK = 1;
; and then falls into the Hold routine


             ; FUNCTION Hold (BEGIN)
                                           ; SOURCE LINE # 9
                                           ; SOURCE LINE # 10
                                           ; SOURCE LINE # 12
;---- Variable 'i' assigned to Register 'R7' ----
0007 7FFF              MOV     R7,#0FFH
0009         ?C0001:
0009 DFFE              DJNZ    R7,?C0001
                                           ; SOURCE LINE # 13
000B         ?C0004:
000B 22                RET
             ; FUNCTION Hold (END)

             ; FUNCTION StartTX (BEGIN)
                                           ; SOURCE LINE # 15
                                           ; SOURCE LINE # 16
                                           ; SOURCE LINE # 17
;---- Variable 'SFRPAGE_SAVE' assigned to Register 'R6' ----


char SFRPAGE_SAVE = SFRPAGE;
0000 AE84              MOV     R6,SFRPAGE
                                           ; SOURCE LINE # 18
SFRPAGE = CONFIG_PAGE;
0002 75840F            MOV     SFRPAGE,#0FH
                                           ; SOURCE LINE # 19
DATA = 1;
0005 D2C9              SETB    DATA
                                           ; SOURCE LINE # 20
                                           ; SOURCE LINE # 21
                                           ; SOURCE LINE # 22
                                           ; SOURCE LINE # 23
SCK = 0;
Hold ();
SCK = 1;
Hold ();
0007 120000      R     LCALL   L?0006
                                           ; SOURCE LINE # 24
DATA = 0;
000A C2C9              CLR     DATA
                                           ; SOURCE LINE # 25
Hold ();
000C 120000      R     LCALL   Hold
                                           ; SOURCE LINE # 26
                                           ; SOURCE LINE # 27
                                           ; SOURCE LINE # 28
                                           ; SOURCE LINE # 29
SCK = 0;
Hold ();
SCK = 1;
Hold ();
000F 120000      R     LCALL   L?0006
                                           ; SOURCE LINE # 30
DATA = 1;
0012 D2C9              SETB    DATA
                                           ; SOURCE LINE # 31
Hold ();
0014 120000      R     LCALL   Hold
                                           ; SOURCE LINE # 32
SCK = 0;
0017 C2C8              CLR     SCK
                                           ; SOURCE LINE # 33
SFRPAGE = SFRPAGE_SAVE;
0019 8E84              MOV     SFRPAGE,R6
                                           ; SOURCE LINE # 34
001B 22                RET
             ; FUNCTION StartTX (END)

The compile did not optimize out the instructions you indicate. Instead, it created common functions for them.

I labeled each instruction with the lines of the C program that are executed.

Jon

Reply

0 Jon Ward over 21 years ago in reply to Sean Warden

When I compiled your example, I got the following:

ASSEMBLY LISTING OF GENERATED OBJECT CODE


             ; FUNCTION L?0006 (BEGIN)
0000 C2C8              CLR     SCK
0002 120000      R     LCALL   Hold
0005 D2C8              SETB    SCK

; The above executes
;   SCK = 0;
;   Hold ();
;   SCK = 1;
; and then falls into the Hold routine


             ; FUNCTION Hold (BEGIN)
                                           ; SOURCE LINE # 9
                                           ; SOURCE LINE # 10
                                           ; SOURCE LINE # 12
;---- Variable 'i' assigned to Register 'R7' ----
0007 7FFF              MOV     R7,#0FFH
0009         ?C0001:
0009 DFFE              DJNZ    R7,?C0001
                                           ; SOURCE LINE # 13
000B         ?C0004:
000B 22                RET
             ; FUNCTION Hold (END)

             ; FUNCTION StartTX (BEGIN)
                                           ; SOURCE LINE # 15
                                           ; SOURCE LINE # 16
                                           ; SOURCE LINE # 17
;---- Variable 'SFRPAGE_SAVE' assigned to Register 'R6' ----


char SFRPAGE_SAVE = SFRPAGE;
0000 AE84              MOV     R6,SFRPAGE
                                           ; SOURCE LINE # 18
SFRPAGE = CONFIG_PAGE;
0002 75840F            MOV     SFRPAGE,#0FH
                                           ; SOURCE LINE # 19
DATA = 1;
0005 D2C9              SETB    DATA
                                           ; SOURCE LINE # 20
                                           ; SOURCE LINE # 21
                                           ; SOURCE LINE # 22
                                           ; SOURCE LINE # 23
SCK = 0;
Hold ();
SCK = 1;
Hold ();
0007 120000      R     LCALL   L?0006
                                           ; SOURCE LINE # 24
DATA = 0;
000A C2C9              CLR     DATA
                                           ; SOURCE LINE # 25
Hold ();
000C 120000      R     LCALL   Hold
                                           ; SOURCE LINE # 26
                                           ; SOURCE LINE # 27
                                           ; SOURCE LINE # 28
                                           ; SOURCE LINE # 29
SCK = 0;
Hold ();
SCK = 1;
Hold ();
000F 120000      R     LCALL   L?0006
                                           ; SOURCE LINE # 30
DATA = 1;
0012 D2C9              SETB    DATA
                                           ; SOURCE LINE # 31
Hold ();
0014 120000      R     LCALL   Hold
                                           ; SOURCE LINE # 32
SCK = 0;
0017 C2C8              CLR     SCK
                                           ; SOURCE LINE # 33
SFRPAGE = SFRPAGE_SAVE;
0019 8E84              MOV     SFRPAGE,R6
                                           ; SOURCE LINE # 34
001B 22                RET
             ; FUNCTION StartTX (END)

The compile did not optimize out the instructions you indicate. Instead, it created common functions for them.

I labeled each instruction with the lines of the C program that are executed.

Jon

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