'bit' type for AVR Microcontroller programming

Question

I have written a code for 8051 microcontroller, where I used bit type, something like this:

static bit done_flag = 0;    /* bit variable */

bit testfunc (               /* bit function */
  bit flag1,                 /* bit arguments */
  bit flag2)
{
.
.
.
return (0);                  /* bit return value */
}

Now I am porting this to ATmega16 AVR controller. I found that there is no support for
bit type in AVR.

AVR-lib C User Manual says:

� Data types: char is 8 bits, int is 16 bits, long is 32 bits, long long is 64 bits, float and double are 32 bits (this is the only supported floating point format), pointers are 16 bits (function pointers are word addresses, to allow addressing up to 128K program memory space). There is a -mint8 option (see Options for the C compiler avr-gcc) to make int 8 bits, but that is not supported by avr-libc and violates C standards (int must be at least 16 bits). It may be removed in a future release.

So what should I do now?

Answer 1

You can use a struct like this:

typedef struct {
    uint8_t bit0:1;
    uint8_t bit1:1;
    uint8_t bit2:1;
    uint8_t bit3:1;
    uint8_t bit4:1;
    uint8_t bit5:1;
    uint8_t bit6:1;
    uint8_t bit7:1;
} BitField;

typedef union {
    BitField asBits;
    uint8_t asByte;
} BitByte;

BitByte mBitField; 

And to access one bit at once you only have to

mBitField.asBits.bit3 = 1

Answer 2

As PeterJ already mentioned in his comment, I would suggest using bool.

You need to include the stdbool library.

#include <stdbool.h>

As already pointed out, in AVRGCC, bool is 8-bit and only an abstraction of an uint8_t. If you can't live with that and need to save every single bit or have tons of global "yes/no" flags (which could indicate bad coding practice), you can consider what Naeriel posted in his answer.

However, using bool and proper variable naming (using the "is"-prefix) produces much cleaner code. For example use

bool IsOperationCompleted;

instead of "done_flag". That way is more obvious to someone who doesn't know the code what exactly the state signals.

Answer 3

Use unsigned char instead. This will use whole byte instead of a bit though.

Answer 4

You can use something like this:

#define bit_get(p,m) ((p)&(m)) #define bit_set(p,m) ((p)|=(m)) #define bit_clear(p,m) ((p)&=~(m)) #define BIT(x) (0x01<<(x))

Usage example:

bit_set(DDRB,BIT(4))

sets PB4 as an output pin.

Source: http://www.avrfreaks.net/