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How do I pass a generic pin argument to a function?

 
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Pavel Kolinko



Joined: 15 Mar 2005
Posts: 10

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How do I pass a generic pin argument to a function?
PostPosted: Fri May 20, 2005 2:10 pm     Reply with quote
I haven't been able to figure out a way to do the following task, which would be very useful in a variety of functions that I have written.

At the moment I am implementing an SPI bus (in software), so I will use it as an example.

Here is a function that sends 1 byte via SPI:

Code:
#define DEV_ENABLE PIN_C5
#define SDATA          PIN_C4
#define SCLK            PIN_C3

/* insert lots of main() code here :grin:  */

void SPI_send8(BYTE data)
{
   BYTE i;
   output_low(ENABLE);

                 for(i=0;i<8;++i)
                        {
                         output_bit(SDATA, shift_left(&data,1,0));
                         output_high(SCLK);
                         output_low (SCLK);
                         }

       output_high(DEV_ENABLE); 
}


Here is the problem:
In order to implement the SPI bus && keep the SPI_send8 function generic, the function needs to know which ENABLE line to use.

I would like to pass to the function an extra argument to make DEV_ENABLE a variable, instead of a constant.
However, I don't want to put an if-else type structure inside the function.
I would like to pass the ENABLE pin address to the function directly.
The problem is that the PINS are all boolean, so I can't pass by reference
(pointers) Sad.


Here is a pseudo code that demonstrates the idea,
but unfortunately is not possible:

Code:
#define DEV1_ENABLE    PIN_C6
#define DEV2_ENABLE    PIN_C5
#define SDATA              PIN_C4
#define SCLK                PIN_C3

int1 *ptr_device_enable_ID;

/* insert lots of main() code here :grin: */


if(DEVICE_1)
  ptr_device_enable_ID=DEV1_ENABLE;
else 
  ptr_device_enable_ID=DEV2_ENABLE;

/* again, lots of other code here */

void SPI_send8(BYTE data, int1 *ptr_device_enable_ID)
{
   BYTE i;
   output_low(ptr_device_enable_ID);

                 for(i=0;i<8;++i)
                        {
                         output_bit(SDATA, shift_left(&data,1,0));
                         output_high(SCLK);
                         output_low (SCLK);
                         }

       output_high(ptr_device_enable_ID); 
}


If I could pass the addresses of the pins in variable/pointer/structure form
to the functions directly,
it would eliminate the need to pass to the functions a bunch of flags.
Writing if-else or switch() for every function to test for the flags
seems like a big waste of ROM, since it is known ahead of time
which data line needs to be used.

Any advice would be much appreciated!
Thanks,
Pavel
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri May 20, 2005 2:19 pm     Reply with quote
Here are some posts that show how to re-write the output_high()
and output_low() functions so they can accept a variable.

Read Mark's post with his functions: my_output_high() and my_output_low():
http://www.ccsinfo.com/forum/viewtopic.php?t=18233

Tomi made a post on this:
http://www.ccsinfo.com/forum/viewtopic.php?t=222
Pavel Kolinko



Joined: 15 Mar 2005
Posts: 10

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PostPosted: Fri May 20, 2005 2:21 pm     Reply with quote
Thank you!
I will check these out!
Ttelmah
Guest
PostPosted: Fri May 20, 2005 2:38 pm     Reply with quote
No 'warranties' here, writing these without testing, but it should be possible to do this with something like:
Code:

#define NUMPORTS (5)

int8 IOarray[numports];
#byte IOarray = 0xF80

#define set_bit(x) IOarray[(x-PIN_A0)>>3]=IOarray[(x-PIN_A0)>>3]|(1<<(x&3))
#define clear_bit(x) IOarray[(x-PIN_A0)>>3]=IOarray[(x-PIN_A0)>>3]&((1<<(x&3))^0xFF)


This for a 18F chip with five I/O ports.

Might be worth an 'experiment'.

Best Wishes
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Fri May 20, 2005 2:42 pm     Reply with quote
I know that you posted some functions too, recently, and I wanted
to post a link to them as well, but I couldn't find them.
Ttelmah
Guest
PostPosted: Fri May 20, 2005 3:13 pm     Reply with quote
Yes, I think I posted some routines earlier, but these macros, are an 'off the cuff' attempt to make a generic form that is compact, and should work with the standard pin numbers from the CCS include file.

Best Wishes
Ttelmah
Guest
PostPosted: Fri May 20, 2005 3:54 pm     Reply with quote
Using the bit set and bit clear functions will make the macros quicker, so:
Code:

#define NUMPORTS (5)

int8 IOarray[numports];
#byte IOarray = 0xF80

#define set_bit(x) bit_set(IOarray[(x-PIN_A0)>>3],(x&3))
#define clear_bit(x) bit_clear(IOarray[(x-PIN_A0)>>3],(x&3))


Or:

Code:

#define set_bit(x) bit_set(*(int8 *)((x-PIN_A0)>>3),(x&3))
#define clear_bit(x) bit_clear(*(int8 *)((x-PIN_A0)>>3),(x&3))


I reckon these must be approaching the simplest versions possible, and ought to work for any of the processors, using the standard pin defintions, passed to functions (as a 'long' though).
So you can for example code:
Code:

void flashbit(int16 bit) {
   set_bit(bit);
   delay_us(50);
   clear_bit(bit);
}

void main(void) {
   int16 pin;
   while (1) {
       for (pin=PIN_A0;pin<=PIN_A5;pin++)
          flashbit(pin);
   }
}

This must be the closest approach to the standard 'fixed' operation, in a simple form. Smile

Best Wishes
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