how do I loop for x seconds?

pico

hey guys,
how do I loop a function for a certain number of seconds?

Thanks!

Tracy Allen

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

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)

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

What about in C?

Phil Pilgrim (PhiPi)

Someone proficient in C will have to answer. I'm not.

-Phil

mikeologist

.

Phil Pilgrim (PhiPi)

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

.

Ariba

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

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