AVR-Chat

Paul Maddox wrote:
> All,
> 
> 
>>   I completely agree with you..... How to organize it ?? Where to put it
>>?? It is a real shame to have this kind of knowledge being lost with time 
>>!!
>>New programmers do not even now how to mask flags in bits !! What about a
>>sister list in Yahoo to keep just the "knowledge bits" ??
> 
> 
> if someone is willing to spend the time, I'm happy to provide space and a 
> subdomain of my server (Www.Synth.Net), I don't have the time to do the 
> webpage and update it, but I can supply the space/bandwidth.
> 
> Paul

I'd like to contribute this bit of code, even though it is not mine.
I got it from here

http://www.dattalo.com/technical/software/pic/debounce.html

   a couple of years ago and have used it ever since:

It is an algorithm for debouncing all the inputs on a port 
simultaneously.  No loops or branches, just inline code.  The routine is 
expected to be called periodically, as by a timer interrupt.

Although the original code is for the PIC, there is an explanation of 
the logic written in C which I repeat here with some small changes for 
clarity.

static unsigned            // global variables
	clock_A,           // counter LSB
	clock_B,           // counter MSB
         temp,              // temporary location
         delta;             // temporary variable
	debounced_state;   // the result you will read

void debounce(unsigned new_sample)
               // new_sample read from port once per call
{

   delta = new_sample ^ debounced_state; //Find all of the changes

   clock_A ^= clock_B;    //Increment the counters
   clock_B  = ~clock_B;

   clock_A &= delta;      //Reset the counters if no changes
   clock_B &= delta;      //were detected.

   temp = (clock_A | clock_B);
   debounced_state = temp;
   //debounced_state &= (clock_A | clock_B);
       //Preserve the state of those bits that are being filtered
       // and simultaneously
       //clear the states of those bits that are already filtered.

   debounced_state |= (~temp & new_sample)
   //debounced_state |= (~(clock_A | clock_B) & new_sample);
       //Re-write the bits that are already filtered.
}

All I can say is that whoever originally came up with this little gem 
has to be some kind of genius.
-- 
erikc