Does the FPGA read/write control act on the root loop/ user interface thread?

[DavidGray]

Hi All,

As the title suggest, Does the FPGA read/write control,  https://zone.ni.com/reference/en-XX/help/371599H-01/lvfpgahost/readwrite_control/,  act on the root loop/ user interface thread?

Looking at, https://zone.ni.com/reference/en-XX/help/371361J-01/lvconcepts/multitasking_in_labview/, it would indicate this, but I'd like to get a proper answer.

Kind Regards

David

[NataliaS]

Hey David,

Could you please clarify what you mean by root loop/user interface thread? Do you mean the host VI?

The FPGA read/write control is function that is used in RT target. 

This thread also questions how this control works, worth giving it a look.

http://forums.ni.com/t5/LabVIEW/Read-Write-Control-Function-in-FPGA-target/td-p/2338222

Ask away if you have any more questions!

Kind Regards,

-Natalia

[Sam_Sharp · Accepted solution]

While I'm not 100% if it acts on the root loop / UI thread - calls to the FPGA (e.g. read/write control, FIFO operations) are definitely blocking. I remember having a weird issue in the past where my FPGA operations were hanging because I was waiting for FIFO data somewhere else.

You should be able to test this fairly easily - try opening a file dialogue while reading from your FPGA. If the read hangs while the dialogue is open, you have a root loop problem.

[DavidGray]

Hi Natalia,

The root loop and user interface thread are discussed http://www.labviewcraftsmen.com/blog/the-root-loop and https://www.winemantech.com/blog/the-ui-thread-root-loop-and-labview-what-you-need-to-know/

The short description is that any user interaction has to go through a serial thread, therefore, no parralisation can occur. For labview, any update to a front pannel object goes through this thread, while block diagram code generally does not, but can be set through the preffered exicution system in VI properties.

Yes, the read/write control goes from the RT block diagram to the FPGA front pannel. What I'm trying to find out is if the fuction has to use the user interface thread/root loop of the RT. My understanding is that the threading of the RT is similar to a winOS.

I've inherited a large application where this has been implimented a lot, so i'm not asking how to use it. My question is what goes on under the hood.

[DavidGray]

Hi Sam,

Thank you for the information and the easy test, I'll give that a go and repost.

I find it hard to belive that a blocking function would not be root loop/UIT related. If it blocked a parrallel thread, the rest of the code would excitute around it. Unless that happened multiple times and blocked every thread.

Kind Regards

David

[Sam_Sharp]

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@DavidGray wrote:

I find it hard to belive that a blocking function would not be root loop/UIT related. If it blocked a parrallel thread, the rest of the code would excitute around it. Unless that happened multiple times and blocked every thread.

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In the case we're talking about here (interfacing with the FPGA), it could be resource lock related serialisation, rather than requiring root loop access - hence why I wasn't sure which one it was. Of course, even a non-reentrant VI being called in multiple places would block execution. If it required root loop - then I would suspect that it might be because it's calling a non-threadsafe DLL in the UI thread under the hood?

[DavidGray]

Sorry, I should have re-read the root loop and UIT webpages https://www.winemantech.com/blog/the-ui-thread-root-loop-and-labview-what-you-need-to-know/.

From that if something is blocking then it'll most likely be on the root loop.