Timer problems

Kram11

Can anyone help?

· I am trying to understand how I can use timers within a program without pausing the code as waitcnt seems to. I have therefore tried to sample the cnt value and compare it to my timed valve required. If the current cnt value plus my timed valve is greater I set a bit and display on the screen.
I seem to be getting a -ve value from the cnt, is this correct?

Is there an easier way of using timers


OBJ
········ tv··· :······ "TV_Text"·
VAR
·long Delay_Start
·byte Delay_Done
·byte Time_Set
·byte Timer1_Complete
·long Start_Point1

CON

··· _CLKMODE = XTAL1 + PLL16X
··· _XINFREQ = 5_000_000
·

·
PUB Main

··· tv.start(12)
repeat
···· tv.Str(string("Delay Time: ",13))
····

····· if ina[noparse][[/noparse]4]· ==1
······· Time_Set:=0·············

·······
· Check_Time
·········· tv.dec(Delay_Start)
··········· tv.out(13)
···········
···········
···· Timer1_On(9_000,1)
·········· tv.dec(Timer1_Complete)
·········· tv.out(13)
·········· tv.dec(Start_Point1)
····

·· tv.out($01)· ' back to home

····
PUB Check_Time
····· Delay_Start := cnt
·····
PUB Timer1_On (Delay1,Start1)
······ if Time_Set==0
········· Start_Point1:=cnt ' check the start time
··· Time_Set:=1· ' the timer is now running
··· if Delay1>(Start_Point1+cnt)
····· Timer1_Complete:=1
··· else
····· Timer1_Complete:=0
······
······

Mike Green

If you're not careful, you can run into problems comparing time values since sometimes the sign bit is set. Better to use time differences like:

PUB startInterval
   Delay_Start := cnt

PUB checkInterval(delay)
   return (cnt - Delay_Start) > delay

deSilva

There are many ways to do these things. You generally use the hardware timer/counters, but you can of yourse also use your technique for slow und unprecise results.

Two remnarks:
(1) Understand that CNT is a wrap-around counter, counting up to POSX and then down from NEGX; a whole cycle takes 40 seconds @ 80 MHz...
Checking

    if Delay1>(Start_Point1+cnt)

as you did is generally a good idea, but it must rather read:

 if Delay1>(CNT -Start_Point1)

You cannot detect delays longer than 25 seconds with this simple technique.

Why is this unprecise? Because you use a lot of SPIN operations inbetwee, so you your accuracy will be araumd some hundred µs.

Erik Friesen

could this be done with one of those old light guns that sense where the gun is aimed by where the vga cathode gun is aimed at a particular time?· Could the vga method somehow feedback to another cog to determine it?

Kram11

thanks for the help.

Erik Friesen

sorry. posted to wrong thread