How to fix error message “__builtin_avr_delay_cycles expects a compile time integer constant make”?

问题

My program isn't being compiled using a GCC AVR compiler. It's a small game on a microprocessor and an LCD screen.

move_delay = 200;
_delay_ms( move_delay );

It doesn't like that this _delay_ms is a variable, but it needs to be a variable because I can adjust the screen action through an ADC. Is there a way I can make it a constant but still usable with the ADC?

回答1:

You could roll you own by looping around the minimal delay you need as often as necessary to get the other delays you need.

void my_delay_ms(int ms)
{
  while (0 < ms)
  {  
    _delay_ms(1);
    --ms;
  }
}

This probably isn't 100% accurate due to time spend for calling _delay_ms() and decrementing ms. But for small ms it might be sufficient.

For larger values of ms you could introduce

void my_delay_ms_10ms_steps(int ms)
{
  while (0 < ms)
  {  
    _delay_ms(10);
    ms -= 10;
  }
}

and so on ...

Also a sort of dynamical approach is possible:

void mydyn_delay_ms(unsigned ms)
{
  unsigned i = 0;
  while (0 < ms)
  {
    if (0 != (ms % 2))
    {
      switch (i)
      {
        case 0:
           _delay_ms(1 << 0);
           break;

        case 1:
           _delay_ms(1 << 1);
           break;

        case 2:
           _delay_ms(1 << 2);
           break;

        /* and so on */

        case <what ever bit-width unsigned uses> -1:
          _delay_ms(1 << (<what ever bit-wdith unsigned uses> -1));
          break;
      }
    }

    ms >>= 1;
    ++i;
  }
}

Update:

Following up vaxquis comment an alternative way to implement the functionality above would be:

void mydyn_delay_ms(unsigned ms)
{
  for (
    unsigned i = 0; /* requires at least C99 */
    0 < ms; 
    ++i)
  {
    if (0 != (ms % 2))
    {
      switch (i)
      {
        case 0:
           _delay_ms(1 << 0);
           break;

        case 1:
           _delay_ms(1 << 1);
           break;

        case 2:
           _delay_ms(1 << 2);
           break;

        /* and so on */

        case <what ever bit-width unsigned uses> -1:
          _delay_ms(1 << (<what ever bit-wdith unsigned uses> -1));
          break;
      }
    }

    ms >>= 1;
  }
}

回答2:

If you use the following define before the #include statement the delay functions can also be called with variables instead of numerical constants:

#define __DELAY_BACKWARD_COMPATIBLE__
#include <util/delay.h>

/************************************************************************
 * Function: sound
 * Description: Toggle Port to generate sound with a given pulse width.
 * Parameter: duration, pulsewidth
 * Uses: _delay_us()
 ************************************************************************/
void sound(uint16_t duration, uint16_t pulsewidth) {
  uint16_t i;
  uint16_t j = 2270 * duration/pulsewidth;

  for(i=0; i<j; i++) {
    SPKR_PORT |= (1 << SPKR_PAD);   //Set port -> create bit mask and OR it
    //delay
    _delay_us(pulsewidth);

    SPKR_PORT &= ~(1 << SPKR_PAD);   //clear port -> negate mask and AND it
    //delay
    _delay_us(pulsewidth);
  }
}

来源：https://stackoverflow.com/questions/30422367/how-to-fix-error-message-builtin-avr-delay-cycles-expects-a-compile-time-inte

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