CODEWITHSUNDEEP
cmacrosbitwise-operatorsavr
MightyPork
MightyPork

Reputation: 18881

Bitwise macro not working (Avr C)

I'm facing some issues with this macro:

#define SHOW(val)   PORTB = ((PORTB & 0xFF^OUT_PINS) | ((val) & OUT_PINS));

Let's say I have (defined earlier)

#define OUT_PINS 0b00011110

and PORTB has some values on other bits that I want to preserve.

The macro was intended to apply val to PORTB (OUT_PINS only) and leave the rest alone.

However, I'm just getting 1's on all output pins.

What's wrong with my code?

Upvotes: 0

Views: 194

Answers (1)

MightyPork
MightyPork

Reputation: 18881

Okay so this was a silly mistake.

#define SEG_DOT     _BV(PB1)
#define SEG_DIAG1   _BV(PB2)
#define SEG_DIAG2   _BV(PB3)
#define SEG_HORIZ   _BV(PB4)

#define BUTTON      _BV(PB0)

#define OUT_PINS    SEG_DOT | SEG_DIAG1 | SEG_DIAG2 | SEG_HORIZ
#define IN_PINS     BUTTON

#define BTN()       (PINB & BUTTON == 0)
#define SHOW(val)   PORTB = ((PORTB & ~OUT_PINS) | ((val) & OUT_PINS));

As you can see the OUT_PINS macro does not have brackets around it, so when it's expanded in the SHOW macro, it all becomes a huge nonsense.

Two possible fixes:

#define OUT_PINS    (SEG_DOT | SEG_DIAG1 | SEG_DIAG2 | SEG_HORIZ)

OR

#define SHOW(val)   PORTB = ((PORTB & ~(OUT_PINS)) | ((val) & (OUT_PINS)));

I like the first fix better, because the second looks very Lispy. Though, why not use both, after all.

Upvotes: 1

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