Saving three bytes of memory with this crazy loop structure..

[mfalkvidd]

An alternative is to move the counter to another hardware resource (a timer, for instance):

void setup() {
  cli();
  TCCR1A = 0;// set entire TCCR1A register to 0
  TCCR1B = 0;// same for TCCR1B
  TCNT1  = 0;//initialize counter value to 0
  // set compare match register for 1hz increments 15624 for 16MHz, 7812 for 8MHz
  OCR1A = 7812;// = (16*10^6) / (1*1024) - 1 (must be <65536)
  // turn on CTC mode
  TCCR1B |= (1 << WGM12);
  // Set CS10 and CS12 bits for 1024 prescaler
  TCCR1B |= (1 << CS12) | (1 << CS10);
  // enable timer compare interrupt
  TIMSK1 |= (1 << OCIE1A);
  sei();
}

volatile uint8_t shouldRun = 1;

ISR(TIMER1_COMPA_vect) {
  shouldRun = 1;
}

void loop() {
  // put your main code here, to run repeatedly:
  if (shouldRun) {
    // ... code that runs every second...
    shouldRun = false;
  }
}

Flash 570 bytes
Ram: 11 bytes
This solution uses 1 byte less (or is it 3 bytes, since it also uses 2 pointers less?) on the stack as well, which might make a difference. But it reserves timer1, which might or might not be OK depending on your application.

[Yveaux]

@mfalkvidd Nice one!

To quote @mfalkvidd : "What I would worry about is the maintainability / readability of the code" ;-)

[alowhum]

Wow, what a response! Amazing stuff!

thanks @mfalkvidd for the explanation.

@Yveaux that millis() / 1000 is very elegant. That's a very interesting direction.

For now though, looking at some of the creations.. I think I'll stick with my modulo system for readability :-D Very cool though.

[tekka]

@Yveaux @mfalkvidd Now it gets ugly - and we are not talking ASM yet... :stuck_out_tongue_winking_eye:

ISR (WDT_vect) {
  WDTCSR = _BV(WDCE) | _BV(WDE); 
  WDTCSR = _BV(WDIF) | _BV(WDIE) | 6; // 1s
  EEARL = 1;
} 

void setup() {
  WDT_vect();
}

void loop() {
    if(EEARL) {
      EEARL = 0;
      // ... code that runs every second...
    }
}

Flash: 502 bytes
Ram: 9 bytes

[alowhum]

@tekka Whoa :-) Can you elaborate what your code voodoo does a little bit?

For a balance of readability, I was pondering how to make this:

• Divide millis() / 1000
• round that down
• get the last bit of that rounded down variable
• if that last bit is different that before, a second has passed.

[Yveaux]

@alowhum that's exactly what my first code snippet does (apart from testing the lowest bit, but you don't need that. Change in seconds is sufficient)

[alowhum]

@Yveaux I know, I really like it. But I was thinking about shaving of another byte somehow :-)

[tekka]

@alowhum Instead of a timer, the watchdog interrupt is used to set a flag on a (in this sketch) not-used eeprom addressing register (EEARL)...certainly not a generic approach, but functional :smiley:

[mfalkvidd]

@tekka so it wouldn't work in a MySensors sketch? That's cheating ;-)

[tekka]

@mfalkvidd Strictly speaking, only @Yveaux's solution would work without modifications to the MySensors core :) But the challenge was weakly defined, so no cheating in that sense :sweat_smile:

[mfalkvidd]

@tekka would it? I verified that my solution worked on a serial gateway. But maybe there was some aspect that I didn't test, that would fail.

[Yveaux]

@tekka I couldn't agree more ;-)
IMHO readability is the differentiator here.

[AffordableTech]

Hi @mfalkvidd,

Problem is, when your code can't compile because you are one (or several) bytes short of ram, nothing else matters.

As to readability, I assume you know about that rarely used compiler feature called 'comments'? I hear they use zero Arduino RAM and even less ROM memory. :flushed:.

Ok, I'm just being cheeky, so don't flame me, it just seemed a good opportunity for a reminder to everybody. Point being we are all guilty of not using enough comments in our code.

You said you are worried about readability and maintainability - it's just like code backups, it's a problem only because we only worry about them 'after' a drive crash, or in the case of comments, two years later when we are trying to remember what the hell this weird code does.. THE REALITY: If we are really worried, we would add liberal comments and do regular backups - otherwise I say we're not really 'that' worried.

Cheers,

Paul