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[Reply #15 on:]

Results:

Code:

Time for digitalWrite(): 4060
Time for true c command: 348
Time for true c command using #define: 348
Time for portWrite(): 2740

[Reply #16 on:]

It seems most of the time is going through the switch();. If I take out the pins I'm not using...

Code:

void portWrite(int pin, int state){
  if (state == 1){ //write HIGH
  switch (pin){
    case 13: PORTB = PORTB | 0x20; break;
  }
  } else {// write low
  switch (pin){
    case 13: PORTB = PORTB & 0xDF; break;
    }
  }
}

...the speed results are impressive:

Code:

Time for digitalWrite(): 4060
Time for true c command: 348
Time for true c command using #define: 348
Time for portWrite(): 352

[Reply #17 on:]

You might be interested in this work on making a "fastDigitalWrite()"...

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1267553811/all

[Reply #18 on:]

Thanks again James. The digitalWriteFast beats all the other options!

Code:

Time for digitalWrite(): 4060
Time for true c command: 348
Time for true c command using #define: 348
Time for portWrite(): 2744
Time for digitalWriteFast(): 288

[Reply #19 on:]

And, one more...
static void portWrite(int pin, int state){

[Reply #20 on:]

What exactly does 'static' do? I ran my little test again, and there was no change in the speed.

[Reply #21 on:]

I ran my little test again, and there was no change in the speed.

Odd.  I expected the optimizer to inline portWrite.  Oh well.

What exactly does 'static' do?

Informs the compiler that the function is only used within the one compilation unit.  In other words, it gives the compiler permission to be more aggressive when optimizing.

[Reply #22 on:]

I have just one more semi-related question...

If the internal 8MHz clock is used on a 328, can the crystal pins be used for I/O using port manipulation?

[Reply #23 on:]

Yes.