How to put current clock ticks in a variable and add 15 seconds to it [SOLVED]

4Alex

Good morning everybody,

I am trying to establish a cyclic reading of a sensor from an infinite loop. Basically, it's a polling sequence and I would like to read a sensor every 15 seconds or so. Timing doesnt need to be precise and I would like to avoid using a cog or any kind of bloated code. I currently have the clock object loaded, but I can't use PauseSec or pause1s, as I don't want to stop the loop from running.

I think the solution could be in reading the current propeller clock number of ticks into a variable and add 15 seconds worth of ticks. I have no idea how to do this nor how many ticks covers a 1 second period. Could someone help me, please.

Here's what I try to achieve, in pseudocode:

repeat
  'check if time to read sensor
  if longVarDelayedClock > longVarCurrentClock
    'read sensor here
    'schedule next reading time in 15 seconds from now
    longVarDelayedClock := longVarCurrentClock + (15 seconds * no_of_ticks_per_sec)
  'do other stuff here
  'and then loop

Many thanks for any assistance.

Cheers,

Alex

Post Edited (4Alex) : 9/8/2009 3:34:26 PM GMT

Timmoore

nexttime := cnt + 15*clkfreq

...

if (cnt - nexttime) > 0
   do sometime

make sure you do the compare by sub and compare with 0 otherwise you get problems when cnt wraps. Also only works to ~25 sec, cnt wraps at ~25sec

Ken Peterson

4Alex: I think there are examples in the Propeller Manual, but here's some simple code:

con
  READ_INTERVAL = _clkfreq * 15

pub main

last_read := cnt
'
'
repeat
  ' check if time to read sensor
  if cnt - last_read > READ_INTERVAL
    'read sensor here
    'record time of reading in clock ticks
    last_read := cnt
  ' do other stuff here
  'and then loop

4Alex

@Timmoore:
Thank you for your assistance. BTW, I use some of your objects: they are well written and very useful. Congrats.

@Ken:
I apologise if the solution was already in the manual. I didn't find it so I guess I was seeing only the one tree instead of the whole forest. I was studying the clock object and coulnd't figure out how to use the various clock commands. I tryied a few things and it turned ugly. I had to implement a variation of your code snippet (because my CON is already defined with _clkmode and _xinfreq) and it works perfectly. For future reference for someone else, here's my code:

CON
  _clkmode      = xtal1 + pll16x
  _xinfreq      = 5_000_000

VAR
  long  last_read
  long  READ_INTERVAL

PUB Main
  READ_INTERVAL := (clkfreq * 15)
  last_read := cnt
  .
  .
  .
  repeat
    if cnt - last_read > READ_INTERVAL
      'read sensor here
      last_read := cnt

Many thanks again for your help.

Cheers,

Alex

Post Edited (4Alex) : 9/8/2009 3:44:44 PM GMT

Ken Peterson

4Alex: You may be missing a repeat statement in your code

4Alex

@Ken: You don't miss much, do you! Yup, I edited the unnecessary code and clipped the repeat. I've corrected the previous posting to reflect this. Thank you so much.

Cheers,

Alex