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cassemblymicrocontrolleravratmega

Programming AVR in C

I'm using an Atmega328. I have output pins that are "randomly" distributed along the pinout, i.e. they don't belong to the same ports. For example, my output pins could be PB0, PB4, PC1, PC3 and PD1.

I have always used Assembly to program microcontrollers, so this would be my first time using C. What I want to know is if there is a way to avoid using DDRx and Px for each pin to set them or clear them.

For example, I would like to use something like this to set the first bit of Port B:

#define NAME_1 DDRB,0

sbi NAME_1;

Is this possible?

EDIT:

Maybe I didn't express myself clearly. What I want is to be able to refer to certain I/O port pins with some meaningful names. For example, name PD3 "blue_LED", so that the code is more readable and, if the blue LED's position is changed later, the code can be easily modified. Stated another way, I want to be able to turn on and off certain pins with their names not being hard-coded. Is there a way?

Solution

  • The sbi instruction is special in that it directly manipulates a bit in an I/O Port on the AVR platform. The normal course with I/O ports is that you have to use other instructions (like out) to copy whole words between the I/O port and a register.

    That said, there's no sbi in C. C just doesn't know about these special features of one particular platform. For the assembly you give as an example, you would write in C:

    DDRB |= 1<<0;

    I personally think this looks quite concise, but of course you COULD define a macro

    #define sbi(x,b) (x) |= 1<<(b)

sbi(DDRB, 0);

    (where b is the "bit number") and maybe the other way around

    #define cbi(x,b) (x) &= ~(1<<(b))

cbi(DDRB, 0)

    This would work, but I recommend not to use it. While the first notation DDRB |= 1<<0; is obvious to any C programmer, using macros like this probably isn't.

    As a final note, if you are concerned about performance: I haven't verified this, but I'm pretty sure avr-gcc is smart enough to emit sbi and cbi instructions when a bit mask operation on an I/O port effectively just changes a single bit. edit: see JLH's answer for an experimental result that gcc-avr indeed is smart enough to emit these sbi/cbi instructions.