Is there a limit to the time span on an asynchronous timer in CVI 7.0?

Question

We're using an asynchronous timer to trigger recording data. TDUMP is
defined as a double (on the UIR) with +/- infinity limits. timedump is
also a double. TDUMP is in minutes, so we multiply by 60 to get seconds.
The code looks like ...
if (LOGSTAT == 0)
uir_err = GetCtrlVal (page_0, LABT0_TDUMP, &timedump);
timedump = timedump * 60;
err = SetAsyncTimerAttribute (g_logTimerID, ASYNC_ATTR_INTERVAL, timedump);
err = SetAsyncTimerAttribute (g_logTimerID, ASYNC_ATTR_ENABLED, 1);
The code works fine for TDUMP values of 7 or less. Somewhere between 7 and
8 the timer starts firing much too quickly. At 10 minutes (600 seconds)
we're seeing triggers at around 171 seconds.
Any suggestions about what the problem is?

Answer 1

Hi all.
Is it only the time before the _first_ callback that is wrong? If so, what is probably happening is this:
1. You disable the timer, which suspends the callbacks
2. You set the interval to a different value
3. You re-enable the timer
From the help for SuspendAsyncTimerCallbacks():
"Stops all timer callbacks until a call is made to
ResumeAsyncTimerCallbacks.
Note: This function does not alter the ongoing schedule of timer
intervals. It merely inhibits the calling of callback
functions."
The new interval will not be implemented until the next timer tick after Step 3 above.
To prevent this happening, you need to call DiscardAsyncTimer(), then when you want to resume, call NewAsyncTimer() with the new interval.
Check out this discussion for more information.
Colin.