LabView Wait (ms) and Wait Until Next ms Multiple behave differently than the Real Time versions. Why?

[kmcdevitt]

The RealTime versions of Wait and Wait Until Next Multiple cause my entire program to slow down, not just the loop that contains the Wait. If I have three loops, each with different Wait times, using the normal Wait(ms) or Wait Until Next (ms) Multiple, then the loops behave as expected without slowing down the other loops. However, if I use the RealTime versions of Wait or Wait Until Next Multiple, then all loops are slowed down when only one of the loop's wait times is increased.

Please see my attached TestRealTimeWaits.vi which demonstrates this "feature". Start it up and then use the radio buttons to switch to the RealTime versions of Wait.

Thanks.

[Arun_V]

Hello,

I ran the attached VI and did not see the results you saw. I have attached a bmp image of the front panle after I ran it on a 8186RT controller.

Also, there is not overhead associated with the RT wait functions, in fact it is supposed to be even better than the normal wait functions. let us see if other have run this program and have gottne different results.

Regards,

Arun V
National Instruments

[kmcdevitt]

Please see your attached bit map. I shows that the other two loops have slowed down with the waits of of more than 10msec, even thought you have selected 2 msec waits for loop 2 and loop 3. The normal LabView waits don't effect the other loops. What's the deal with the RealTime versions?

[Arun_V]

Hello Kmcdevitt,

Do you have the 7.1.1 maintenance realease installed? The reason I am asking this is, the dlls associated with the timing VIs where non-reentrant in 7.1 and this might cause it to be shared and if we use it in many instances then the resources would be shared forcing it to wait longer than it should. This was fixed in the 7.1.1 realease which is available for free on our website. Make sure you download it both for LabVIEW 7.1 and RT 7.1 too.

Regards,

Arun V
National Instruments

[TommyHelter]

I have also experienced troubles with the RT time functions while running on the FieldPoint series. My approach was to check my execution thread and priorities. Also, the Wait (as apposed to the Wait Until Next Multiple) function seems to cause an entire thread to wait. Here is an article that offered great help for me. The article does not mention using the RT time functions and it is my perception that, with thread priority set to approximately "normal" that these timing functions and threads are yielding to other processes - including host commuications, etc.

Timed Loops
http://zone.ni.com/devzone/conceptd.nsf/webmain/E83351E12CD2D50886256B66006E4D15

TommyH

[kmcdevitt]

The link below refers to the LabVIEW versions of Wait, not the Real-Times versions of Wait and Wait Until Next Multiple:

http://zone.ni.com/devzone/conceptd.nsf/webmain/E83351E12CD2D50886256B66006E4D15

I have applied the Maintenance Releases to update both my LabVIEW and LabVIEW Real-Time from 7.1 to 7.1.1. This seems to have solved the problems.

[TommyHelter]

Yes, I realized that the article is referring to the LabView versions of Wait, etc., but the article specifically mentions the Real-tImm environment. Thanks for your input on the upgrades. Much appreciated.

TommyH