how do I loop for x seconds?

Comments

• Tracy Allen Posts: 6,667

  2018-02-11 00:08 edited 2018-02-12 17:50

  We probably need more information in order to answer that. One common way to do that refers to the system clock register.

  ticks := clkfreq * Nseconds + cnt  ' the system clock at N seconds in the future
      ' provided the cnt <2^32,  ~(53/2) seconds at clkfreq=80MHz
  repeat
    ' do whatever
    if cnt - ticks > 0   ' wait that number of seconds with uncertainty for the whatever code
      quit
  
• tomcrawford Posts: 1,129

  2018-02-11 00:09

  1. Put a waitcnt in the function to force it to take a known amount of time.
  2. repeat the loop 1_000 or 1_000_000 divided by the know loop time.
• Phil Pilgrim (PhiPi) Posts: 23,514

  2018-02-11 00:23

  In Spin,
  
  If x < 27, use this:
  

  t0 := cnt
  repeat until (cnt - t0 => x * clkfreq)
    'Do stuff for x seconds
  

  
  Otherwise, this:
  

  t0 := cnt
  repeat x
    repeat until (cnt - t0 => clkfreq)
      'Do stuff for x seconds
    t0 += clkfreq
  

  
  In both cases, it's assumed that "do stuff" doesn't take very long to perform.
  
  -Phil
• pico Posts: 29

  2018-02-11 00:30

  What about in C?
• Phil Pilgrim (PhiPi) Posts: 23,514

  2018-02-11 00:46

  Someone proficient in C will have to answer. I'm not.
  
  -Phil
• mikeologist Posts: 337

  2018-02-11 01:00 edited 2018-02-11 02:09

  .
• Phil Pilgrim (PhiPi) Posts: 23,514

  2018-02-11 01:39

  mikeologist,
  
  Um, if ints are signed, that won't work. Also, even if ints are unsigned, that code is only good for times less than 54 seconds.
  
  -Phil
• mikeologist Posts: 337

  2018-02-11 01:53 edited 2018-02-11 02:08

  .
• Ariba Posts: 2,694

  2018-02-11 04:53

  It's an easy translation from Phils Spin code to C:
  
  The first one with x < 27 seconds:

  int t0 = CNT;
  while (CNT - t0 < x * CLKFREQ)
  {
    //Do stuff for x seconds
  }
  
• iseries Posts: 1,513

  2018-02-11 11:14

  This function if available on Arduino as micros and millis.
  
  I needed to keep track of the time and then do something and I needed multiple timers to do it so I wrote a library function for it.
  

  int micros(unsigned long *D)
  {
    long t;
    
    t = CNT + 280 - *D;
    *D = CNT;
    if (t < 0)
      t = UINT32_MAX + t;
  
    *D = *D - t % us;
    t = t/us;
    return t;
  }
  
  int millis(unsigned long *D)
  {
    long t;
    
    t = CNT + 280 - *D;
    *D = CNT;
    if (t < 0)
      t = UINT32_MAX + t;
  
    *D = *D - t % ms;
    t = t/ms;
    return t;
  }
  

  
  Buy passing in a long variable you can keep track of multiple time instances.
  

  unsigned long PCNT;
  unsigned long P2CNT;
  
  
  int main()
  {
    int sec, sec2;
    
    int d1, d2;
    micros(&PCNT);
    millis(&P2CNT);
    
    sec = 0;
    sec2 = 0;
    d1 = 0;
    d2 = 0;
    
    while(1)
    {
      d1 += micros(&PCNT);
      d2 += millis(&P2CNT);
      
      if (d1 > 1000000)  // wait a second
      {
        d1 = d1 - 1000000;
        print("Timer: %d, %d\n", d1, sec++);
      }      
      
      if (d2 > 1000) // wait a second
      {
        d2 = d2 - 1000;
        print("Timer2: %d, %d\n", d2, sec2++);
      }      
    }  
  }
  

  
  You can also use the mstimer.h library that starts a cog with the time in it.
  
  Mike