Labview Video Tutorial? Dashboard

[Kingofl337]

Here is a sample on how to write user bytes in easyC.

[Abrakadabra]

Hi Danny -

Thanks for the tutorial. It went a little fast in places so we had to watch it a few times, but we finally got a finished product that looks almost exactly like yours. However, when we run, we get a few seconds of data transmission and then an error:

Error -1073807252 occurred at VISA read
in PacketReader.vi -> DashboardProvider.vi
Possible Reasons
An overrun error occurred during the transfer.
A character was not read from the hardware
before the next character.

At this point the DashboardProvider is halted, but the Dashboard itself is still going.

We are using the USB<->Serial converter cable sold by IFI for the VEX system. Could that be the issue? Has anyone else had any luck with this adapter?

(It's getting real hard to find a decent but inexpensive laptop with a real serial port!)

Thanks for any guidance you can provide!

[Danny Diaz]

Okay, I'm going to shoot from the hip here since I cannot test it right now - the only thing I can think is happening is that I forgot to put a wait in the while loop. The program runs fine on my dual core laptop, but I haven't checked to see if one cores is pegged out. See, when you create a while loop you're supposed to put some kind of wait or blocking call in it so that the while loop doesn't just spin and eat all the processor (that way the thread running the loop yields for other threads in the system to be able to run). Open the Dashboard Provider VI and you'll see what I mean, the while loops there have a "wait for millisecond multiple" and usually it has 10 wired into it (that means the processing within the loop will be suspended until the next 10 ms multiple). I had thought the "Dashboard Read" VI would take some time to read the datasocket variable (actually I thought it was a blocking call), but I could be incorrect - if this is the case then the thread reading the datasocket variable in your while loop is using a significant amount of the processor and it is starving the serial port read; that's why the overrun is probably happening (you can verify this by watching your CPU utilization while you're running the VI). On a dual core target if you're lucky and the serial read happens to be running on one processor and the datasocket read hogs the second processor, everything will run fine. However, if you're on a single core target then you're in for some serious trouble, which is probably what's happening to you (or you're unlucky and both threads got scheduled on the same processor).

I won't be able to get my hands on the testing platform again until Saturday, so if this is the case I'll update the video then with this new code. Until then, please accept this new VI (attached) and let me know if this solves your problem.

-Danny