Reassign Port Variable In Function?

[chief 0]

Hi, I have 2) one wire digital sensors, one on Port E.1 and the other on E.2 . I'm calling the read function with argument 1 for inside sensor or 0 for outside sensor. This is just a snippet of the code - If I change sens in the read function to in_sens, so it works for only the inside sensor, it works fine, but I've been trying to figure out how to make the function work for either sensor, and I'm stuck. sens = in_sens didn't work, a pointer didn't work (at least the way I did it). Can anyone offer a suggestion?

 

 
volatile bit out_sens @ PORTE.1
volatile bit in_sens @ PORTE.2

void read(char n)
{

if (n == 1) //?? this is where I'm stuck - if n == 1 I need to assign the variable sens to in_sens; if it's 0, assign sens to out_sens.

if (!sens) fail(1); //sensor not ready
//make sens output, pull down for 1.1mS to trigger sensor
if (n == 1) clear_bit(trise,2);
 else clear_bit(trise,1);
sens = 0;
 delay_ms(1);
delay_100us(1);
if (n == 1) set_bit(trise,2);
 else set_bit(trise,1);  // set sens back to input
do //check for start of acknowledge pulse (spec 20-40us)
 {
  if (count > 4) fail(2); //no acknowledge
  count++;
  delay_10us(1);
 }while (sens);

[Pavel 0]

I'd use bitwise operations:

 

#define OUT_MASK 1
#define IN_MASK  2

void read(unsigned char mask)
{

if (!(porte & mask)) fail(1); //sensor not ready
...
}

//Read inside sensor
read( IN_MASK );

//Read outside sensor
read( OUT_MASK );

 

Regards,

Pavel

[chief 0]

I'd use bitwise operations:

 

#define OUT_MASK 1
#define IN_MASK  2

void read(unsigned char mask)
{

if (!(porte & mask)) fail(1); //sensor not ready
...
}

//Read inside sensor
read( IN_MASK );

//Read outside sensor
read( OUT_MASK );

 

Regards,

Pavel

 

Thank you Pavel for pointing me in the right direction. I don't have it working yet, but I'm reading up on mask operations to figure out where I went wrong.

 

Best regards,

 

Brian

[Pavel 0]

Another option is to use function templates. This will make code much simplier compared with bitwise approach but internally code for 2 copies of the function will be generated. If you don't care about code space or your function is really small go with function templates:

 

#define OUT_PORT 0
#define IN_PORT  1

template <unsigned char BitPosition>
void read(void)
{
volatile bit sens @ PORTE.BitPosition;


if (!sens) fail(1); //sensor not ready
...
}

//Read inside sensor
read<IN_PORT>();

//Read outside sensor
read<OUT_PORT>();

[chief 0]

I'd use bitwise operations:

 

#define OUT_MASK 1
#define IN_MASK  2

void read(unsigned char mask)
{

if (!(porte & mask)) fail(1); //sensor not ready
...
}

//Read inside sensor
read( IN_MASK );

//Read outside sensor
read( OUT_MASK );

 

Regards,

Pavel

 

Hi Pavel,

I now have it working using bit masks. It was a learning experience, but that's a good thing - I learned something I didn't know before! (porte & mask) returns the weight of the bit, not 1 or 0. See my changes and comments to your example below. Thanks for your help!

 

#define OUT_MASK 2 // for bit 1 - mask needs to be the WEIGHT of the bit, not the number. Ex: bit 1 is mask 2, bit 2 is mask 4, etc.
#define IN_MASK  4 // for bit 2

void read(unsigned char mask)
{

if (!(porte & mask)) do_something_if_bit_is_lo; // this will test for all mask bit(s) = 0

if ((porte & mask) != mask) do_something_if_mask_bits_don't_match_mask; // this is a more explicit test, and for >1 bit mask

if ((porte & mask) == mask) do_something_if_all_mask_bits_match_mask; // this is a test for matching all mask bit(s) or testing even just one bit for 1.
...
}

//Read inside sensor
read( IN_MASK );

//Read outside sensor
read( OUT_MASK );