Calculated timeout from repeat loop

average joe

I'm a bit lost on the best way to handle a timeout from a repeat loop. Basically, I'd like to repeat until a condition is true, or a timeout period has elapsed. My trouble is handling a clock wraparound.

Example :

PRI GetMark | tout
  tout := _syncTimeout
  tout += cnt
  repeat
    RX(@d)  
  until GetPacketType == _mark  or (cnt > tout)

This will work perfectly fine, as long as cnt + _syncTimeout is less than $7FFF_FFFF. If not, it causes tout to be evaluated improperly. I've been thinking about the best way to do this and still drawing a blank. Any help would be greatly appreciated as always!

kuroneko

Provided your timeout stays in range (e.g. ~27sec @80MHz) this should do. Just make sure you compare against the delta, never absolute values.

PRI GetMark | tout
  tout := cnt
  repeat
    RX(@d)  
  until GetPacketType == _mark  or ((cnt - tout) > _syncTimeout)

average joe

I knew there was an easy way to handle it, just couldn't think how. Thanks again. I owe ya big time

JonnyMac

This is just re-arranging terms... how I tend to do it (with butt-obvious code).

t0 := -cnt
  repeat
    ' do something
    elapsed := t0 + cnt
    if (elapsed => TIME_OUT)
      return TO_CODE