[sdcc-devel] [ sdcc-Support Requests-2897090 ] PIC14-PIC16 bitwise manipulation of registers and variables

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Support Requests item #2897090, was opened at 2009-11-13 09:21
Message generated for change (Comment added) made by tecodev
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Category: None
Group: None
Status: Open
Priority: 5
Private: No
Submitted By: z-control (z-control)
Assigned to: Nobody/Anonymous (nobody)
Summary: PIC14-PIC16 bitwise manipulation of registers and variables

Initial Comment:
Hi
I am comming from CCS and GNUAVR, and I am missing some background about how to manipulate bit-level registers or variables.

Typically, the pic has the ASM functions such as BCF, BSF, BTFSC, BTFSS.

I currently only see a solution to read a full byte (register or variable) to set or clear or test a bit, for set or clear write it back to the right place.
Also I would like to not only set or clear a given bit, ie RA1 or RA2, but make this variable.
Ie, I want to have a routine that sets or clears a bit 1,2,3,4... in a raw.

In GNUAVR, I know the _BV function, in CCS, you find BIT_SET(reg+var/reg,bit), BIT_CLEAR(reg+var,bit), BIT_TEST(reg+var,bit).

is this a missing function in SDCC ?

Thanks for any help.


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>Comment By: Raphael Neider (tecodev)
Date: 2009-11-13 14:59

Message:
What does "does not work" mean?

If all the PORTB-pins are 0, you might not have set them up as digital
pins. Try
ANSEL=ANSELH=0;
before modifying the register (ANSELH is the important one for PORTB, see
datasheet):
If you assign tmp to PORTB, the hardware overwrites all bits and you are
fine.
If you clear individual bits, the hardware executes read-modify-write and
-- unfortunately -- all pins read as 0 when configured as analog inputs
(the power-on default, ANSEL=ANSELH=0xff).

BTW: If you want to specify the bit to modify at runtime, the hardware
cannot use BCF/BSF/BTF/... because these require a literal (compile-time
constant) bit index. The compiler will generate a loop for (1 << (BIT)) and
modify the PORT via IORWF or ANDWF instead.

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Comment By: z-control (z-control)
Date: 2009-11-13 12:00

Message:
thank you for the input, I must make something wrong as I tried your code
couple of days ago. I just checked again and copied the 2 options I had out
 of an interrupt routine:
...
#define BIT_SET(VAR, BIT)     VAR |= (1 << (BIT))
#define BIT_CLR(VAR, BIT)     VAR &= ~(1 << (BIT))
#define BIT_TST(VAR, BIT)   ((VAR) & (1 << (BIT)))
....
   if(++raw==8)raw=0;
   tmp=0xff;
   tmp=tmp ^ (1 << raw);  // enable led raw (active low)
   PORTB=tmp;
//the above code works, each bit of PORTB gets 0 in a raw.
// but with your macro it would be simpler but that does not work !
// is it only limited to variables and not to registers ? 
   PORTB=0xff;
   BIT_CLR(PORTB,raw);
// should do the same, but does not work
// I am using a 16f887

P.S. with VAR/REG I ment applicable to variables and PIC registers within
SDCC.


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Comment By: Raphael Neider (tecodev)
Date: 2009-11-13 10:31

Message:
Hi,

you can use

#define BIT_SET(VAR, BIT)     VAR |= (1 << (BIT))
#define BIT_CLR(VAR, BIT)     VAR &= ~(1 << (BIT))
#define BIT_TEST(VAR, BIT)   ((VAR) & (1 << (BIT)))

SDCC will automatically replace single-bit accesses with the
bit-manipulation instructions offered by the target architecture.

I do not know what 'reg+var' is supposed to mean, but the above should get
you started.

Best regards


Raphael

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