NI USB-7855R - "The current target does not support shared variables"

[cslowa]

Hi Everyone,

I'm trying to share a few boolean values between a host application and an FPGA using shared variables. However I get the error when trying to build:

I can't seem to find much info about this error, or why the NI USB-7855R doesn't support the SVE.

Any information would be appreciated.

[crossrulz]

FPGA does not support Shared Variables.  You can just use front panel controls to pass tag data to the host.

[cslowa]

I'm currently passing data to the FPGA from the host using the Read/Write Control from the FPGA Interface Pallet and this works, but it's slow.

The write takes about 4ms. 

Are you saying I can just drop the FPGA's VI into the Host's block diagram and integrate it like any other VI? I tried to do this the other day and ran into problems. If this should be possible, please let me know and I can explain what was going on.

[crossrulz]

---

@cslowa wrote:

I'm currently passing data to the FPGA from the host using the Read/Write Control from the FPGA Interface Pallet and this works, but it's slow.

The write takes about 4ms.

---

That is the way to do it.  4ms does seem like a long time though.  It could be from Windows or even the USB bus.

You may want to try using a DMA FIFO to pass data down to the FPGA.  You will have to add overhead to state what the data is as you pass it down (ie build up a message and send the message through the FIFO).

[cslowa]

Noted. I appreciate the help.

I will leave things the way they are - maybe when we get our production hardware [PXI chassis and junk], the Read/Write Control function will be faster with that configuration.

Either way, the 4ms isn't killing me, but that single call slows down my main thread by a factor of 2' all because of one call.

Thanks again!