AVR-Chat

I think so.  Are you trying to do something like this?
The code compiles under WINAVR.
(apologies for being a smartass  :D )

// code begins //

#include <avr\pgmspace.h>
#include <avr\io.h>
#include <avr\interrupt.h>

#define true 1
#define false 0

char    last_one;	// previous encoder sample
char    fault;		// goes high when both lines change at once
int     count;		// motion accumulator

void idle( void) {}     // dummy for encoder not moving

void encoder( char * port, char pin1, char pin2)
{
     char    this_one;	// current encoder sample
     char    bit_3, bit_2, bit_1, bit_0;

     last_one = this_one;
     this_one = *port;

     bit_3 = this_one & pin1;
     bit_2 = this_one & pin2;
     bit_1 = last_one & pin1;
     bit_0 = last_one & pin2;

     if( bit_3)
     {
         if( bit_2)
         {
             if( bit_1)
             {
                 if( bit_0) count++;
                 else idle();
             }
             else
             {
                 if( bit_0) fault = true;
                 else count--;
             }
         }
         else
         {
             if( bit_1)
             {
                 if( bit_0) idle();
                 else count--;
             }
             else
             {
                 if( bit_0) count++;
                 else fault = true;
             }
         }
     }
     else
     {
         if( bit_2)
         {
             if( bit_1)
             {
                 if( bit_0) fault = true;
                 else count++;
             }
             else
             {
                 if( bit_0) count--;
                 else idle();
             }
         }
         else
         {
             if( bit_1)
             {
                 if( bit_0) count--;
                 else fault = true;
             }
             else
             {
                 if( bit_0) idle();
                 else count++;
             }
         }
     }
}

int main( void)
{
     encoder( &PORTB, 0x08, 0x04);
}

// code ends //



Jeff Blaine wrote:
> erikc,
> 
> In this project, yes they are together.  But that's not always the case.  If I can't find a better solution, then I will just set the routeene to work with a 2x4 pair and provide it an "encoder number" which would resolve to A0/A1 for encoder 1, A2/A3 for encoder 2, etc.  That's easy.  But given I use a rotary in almost everything now, I'm trying to move toward a function which would not have any prespecified index.  
> 
> Now that I think of it, I suppose I could set it up with arguments PORT, pin A, pin B.  
> 
> Something like this:  char encoder_service(char *avr_port, unsigned char bit_mask_A, unsigned char bit_mask_B) 
> 
> Which would then be called as (example):
> 
> x = encoder_service(&PORTA, 0x01, 0x02);
> 
> Think that would work?
> 
> 73/jeff/ac0c
> www.ac0c.com
> 
> 
> 
> From: erikc 
> Sent: Friday, August 06, 2010 7:45 AM
> To: AVR-Chat@yahoogroups.com 
> Subject: Re: [AVR-Chat] passing an AVR port's bit pointer to to a function
> 
> 
>   
> Will the port bits both be on the same port or can they be on 
> different ports? If so, it seems to me that the best way to go would 
> be to pass the port bits as a bit mask (i.e. pin7 = 0x80 rather than 
> pin7 = 7) and do it that way.
> 
> erikc
> 
> Jeff Blaine wrote:
>> I have an encoder service function that reads a couple of bits from an AVR and increments a counter if a turn was decoded.
>>
>> To make the function generic, I would like to pass the port bits as arguments to the function.
>>
>> Unfortunately, I cannot quite figure out how to pass the port bits to the function. Appreciate advice as to what I'm overlooking...
>>
>> function prototype looks like this:
>>
>> char encoder_service(char *avr_port_bit_A, char *avr_port_bit_B) {
>>
>> }
>>
>> In the main program, I would have something like this to call the function
>>
>> x = char pointer to PORTA0
>> y = char pointer to PORTA1
>>
>> encoder_service( x , y );
>>
>> Using standard C.
>>
>> 73/jeff/ac0c
>> www.ac0c.com