ICCV7 C Best or Better way to get a pin input state.

TJHJ · 2009-03-29 17:07

I have got to be making this harder than it is, but I cant seem to find a pre defined method in the include files for getting a pin input state. Have I just been missing it? If not the only way I can seem to come up with to get a pins state from INA seems clunky.

Here is how I am currently doing it.


int getPinState(int pin)
{
int pinMask;

pinMask = 1 << pin;

if ( (INA & pinMask) == pinMask) 
   {
   return 1;
   }
else 
   {
    return 0;
   }


}

It just seems like a waste of operations to get a pin state.

Any suggestions or ideas would be greatly appreciated as always.

TJ

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Mike Green · 2009-03-29 17:14

Because C, like Spin, treats a non-zero value as true, you could say:

int getPinState(int pin) {
return INA & (1 << pin) }

This is the way it would be done in assembly or Spin. Alternatively, you could have:

int getPinState(int pin) {
return (INA & (1 << pin)) != 0 }

You could also use the C macro preprocessor to do:

#define getPinState(pin) ((INA & (1 << pin)) != 0)

and let the compiler's optimizer improve the efficiency, particularly if pin is a constant.

Post Edited (Mike Green) : 3/29/2009 5:20:40 PM GMT

virtuPIC · 2009-03-29 18:35

Right, Mike. That's the easy way to get the pin value as boolean true or false. If you need the value as int 1 or 0 - maybe you merge several pin values or use it for masking - then it gets only a little more complicated:

int getPinState(int pin) { 
 return (NA & (1 << pin)) >> pin;
}

This should only be one more instruction in compiled code.

If pin is a constant the following code to be faster on the prop if the compiler does some optimization:

#define PIN 3 
int getPinState(int pin) {
  return (NA & (1 << PIN) ? 1 : 0;
}

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mpark · 2009-03-29 22:06

To get 1 or 0 this might be a little faster:

int getPinState(int pin) { 
 return (INA >> pin) & 1;
}

jazzed · 2009-03-29 23:36

Nice optimization mpark. Remember that all function calls have overhead. The macro like Mike mentioned may make code bigger if used several times, but will be faster than a function ... just watch out passing values to some macros and check your friendly C reference for problems. #define GETBIT(pin) ((INA >> (pin)) & 1) /* pin >= 0 && pin < 32 */

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TJHJ · 2009-03-30 23:23

Thanks all, mpark that works perfectly for what I wanted.

Thanks again,
TJ

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
I owe everyone here a bunch, So thanks again for answering my dumb questions.
Projects. RG500 ECU system. PropCopter. Prop CanSat. Prop Paste Gun.
Suzuki RG500 in a RGV 250 frame.
Bimota V-Due (Running on the fuel injection system)
Aprilia RS250

ICCV7 C Best or Better way to get a pin input state.

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