What's going on?

what's going on?

i purchased nice new digital scope, , thought i'd @ arduino nano's speed performance.

here's code  - toggling pin in various ways.

code: [select]


//1: newfile1,2,3.png


void loop() {
  while (1) {
    portd |= 0x20;
    //digitalwrite( pulsepin , high);
    portd &= 0xcf;
    // digitalwrite( pulsepin , low);


  }

}


//2:newfile4.png

void loop() {
  while (1) {

    //digitalwrite( pulsepin , high);
    portd &= 0xcf;
    // digitalwrite( pulsepin , low);

    portd |= 0x20;
  }

}



//3:newfile5.png


void loop() {
//  while (1) {

    //digitalwrite( pulsepin , high);
    portd &= 0xcf;
    // digitalwrite( pulsepin , low);
    portd |= 0x20;
//  }

}


//4:  newfile6.png

void loop() {
  //  while (1) {
  portd |= 0x20;
  //digitalwrite( pulsepin , high);
  portd &= 0xcf;
  //digitalwrite( pulsepin , low);

  //  }

}



//5:  newfile7.png

void loop() {
//  while (1) {
//    portd |= 0x20;
    digitalwrite( pulsepin , high);
//    portd &= 0xcf;
    digitalwrite( pulsepin , low);

//  }

}



note 5 versions . vary in use direct port writes vs digitalwrite, , in embedding of while(1) inside normal loop{} test that's performance.

the scope pictures appended.

some things become clear.

digitalwrite incredibly slow.    6-8us write pin . that's around 100 instructions @ 16mhz ( checked - 15.973mhz - pretty good)

 why?

the loop{} seems take 6 go round - why?  - it's jump label.

the while(1) reasonably ok - test 'one' seems take 1 instruction.

there's continuous processor stop every millisecond or - presumably corect millis() count. takes again 8us - it's simple interrupt incrementing counter - doesn't take 100 instructions!

just curious - , can turn millis() stuff off time critical stuff doesn't need it?

allan

we aware digitalwrite() slow - seems reasonable price convenience.

it seems me detailed explanations , other questions lie in study of arduino source code included ide.

a lot of arduino system focused on convenience rather absolute performance.

i presume can modify source code prevent millis() working if necessary.

...r

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