topic Re: How to do arbitration in LabVIEW FPGA in LabVIEW

How to do arbitration in LabVIEW FPGA

vicky2889 — Tue, 13 Jan 2026 16:15:16 GMT

Hello Everyone,

I want to do arbitration in LabVIEW FPGA. But i am not getting how to do that, i searched for that but unable to understand exactly from where i can select arbitration options out of the three arbitration options available in LabVIEW FPGA: Always Arbitrate, Arbitrate if Multiple Requester's only and Never Arbitrate.

Friends i am unable to find from where i can select all these options or i have to design these options.

Please help me in this regard.

I have seen these pages

https://www.ni.com/docs/en-US/bundle/labview-fpga-module/page/understanding-arbitration-options-fpga-module.html#d10375e100

http://zone.ni.com/reference/en-XX/help/371599K-01/lvfpgaconcepts/arbitration_timing/

Thanks
VIKAS

Re: How to do arbitration in LabVIEW FPGA

wiebe@CARYA — Mon, 07 May 2018 08:04:51 GMT

The node is defined in the project. The item is configured there. Where you configure it, there is a tab to set the arbitration.

Re: How to do arbitration in LabVIEW FPGA

vicky2889 — Mon, 07 May 2018 08:43:57 GMT

Thanks

So, if there are four request lines to the system requesting simultaneously. In that we want to give the acknowledge to the one which sent the request first, then to the line which sent the request after first etc.

for four I/O lines we have to take four I/O connectors.

In that case we have to set the arbitration option (like arbitrate if multiple requests only ) in all four I/O connectors ??. Also i don't know how to connect all four I/O connectors together so that the arbitration done for 4 I/O lines.

Can you please help me in this regard?

Thanks

Re: How to do arbitration in LabVIEW FPGA

wiebe@CARYA — Mon, 07 May 2018 09:09:09 GMT

@vicky2889 wrote:

So, if there are four request lines to the system requesting simultaneously. In that we want to give the acknowledge to the one which sent the request first, then to the line which sent the request after first etc.

for four I/O lines we have to take four I/O connectors.

In that case we have to set the arbitration option (like arbitrate if multiple requests only ) in all four I/O connectors ??. Also i don't know how to connect all four I/O connectors together so that the arbitration done for 4 I/O lines.

Can you please help me in this regard?

We can help, but we need a bit more information.

I usually try to put everything in single-cycled-timed-loops (SCTL). As long as each I/O node is accessing a unique port, you don't need arbitration at all. And since it's all in a SCTL, it's all effective at the exact same time so you don't need synchronization either.

You can even put all I/O nodes in a SCTL, and communicate values to it from another loop (for instance if the SCTL is too fast to fit everything in it).

I think things are a lot easier that you seem to think, but I could be wrong (I don't know exactly what you thing is needed, and also don't know everything about FPGA).

Some code would be helpful...

Re: How to do arbitration in LabVIEW FPGA

vicky2889 — Tue, 08 May 2018 03:09:08 GMT

Actually i want to do arbitration for 6 devices.

There are 6 request lines from 6 devices, i will connect all request lines to the DAQ FPGA card. Now i want to give acknowledge first to that device which sent the request first, then to that device which sent the request at second number.

e.g. there are six devices named as dev1, dev2, dev3, dev4, dev5, dev6. Then assume dev3 sends request to the DAQ FPGA card first then dev6 sends so in that case i want to give the acknowledge to the dev3 first and then dev6.

Re: How to do arbitration in LabVIEW FPGA

wiebe@CARYA — Tue, 08 May 2018 08:47:31 GMT

@vicky2889 wrote:

Actually i want to do arbitration for 6 devices.

There are 6 request lines from 6 devices, i will connect all request lines to the DAQ FPGA card. Now i want to give acknowledge first to that device which sent the request first, then to that device which sent the request at second number.

e.g. there are six devices named as dev1, dev2, dev3, dev4, dev5, dev6. Then assume dev3 sends request to the DAQ FPGA card first then dev6 sends so in that case i want to give the acknowledge to the dev3 first and then dev6.

That's a bit too high level to tell where\if you need arbitration. This can be implemented in hundred different ways. I've done a lot on FPGA, but never needed arbitration on I/O.

Re: How to do arbitration in LabVIEW FPGA

Intaris — Tue, 08 May 2018 11:47:42 GMT

I don't think arbitration does what you think it does.

If you would activate arbitration for all four IO lines, you can simply have all 4 "writers" writing to them "in parallel" and LV FPGA will figure out which one gets control. This will have nothing to do with any "acknowledge" you might want to implement.

I recommend: Implement 4 input lanes. Have a single loop iterate through all four inputs and as soon as one is active, send it to the appropriate IO (preferably the data being sent will include which IO it's for). Then it sends an acknowledge to that sender before iterating on to he next one. Your iterating loop in between is then a mediator. You need a mediatior isntead of arbitration because it seems you want a two-way communication. AFAIK, Arbitration is for unidirectional communication only, but I may be wrong because I've never actually used it.

But a more general question, what is the nature of the "acknowledge" in your design?

Re: How to do arbitration in LabVIEW FPGA

vicky2889 — Tue, 08 May 2018 16:17:11 GMT

But how we decide that which one is receiving request first out of five devices. Can we have to use case statements for all this in FPGA VI or some other way ??

Secondly, can you please tell me the exact working of arbitration options in FPGA I/O?

If we set arbitration in one FPGA I/O how this arbitration works ?

I want to use acknowledge in my task because the transmission of data from particular devices depends on this acknowledge e.g if dev2 receives acknowledge first the data will be transmitted from dev2 first.

Re: How to do arbitration in LabVIEW FPGA

Intaris — Tue, 08 May 2018 21:13:31 GMT

It almost sounds like you want events on FPGA. Doesnt work like that. Polling is really all you can do.

Re: How to do arbitration in LabVIEW FPGA

vicky2889 — Wed, 09 May 2018 02:09:12 GMT

No you getting me wrong.

I don't need events on FPGA, i just want to receive request from devices to fpga and want to send acknowledge from FPGA to devices.

When the device receive acknowledge from FPGA, the device sends the events not from FPGA.

Secondly can you please tell me the exact working of arbitration in FPGA I/O as arbitration options are available on every FPGA I/O node, so whats the use of arbitration on one node itself.

Re: How to do arbitration in LabVIEW FPGA

GerdW — Wed, 09 May 2018 06:18:58 GMT

Hi vicky,

how we decide that which one is receiving request first out of five devices.

You read your 6 digital inputs as fast as the FPGA or the module allows, I often also read the full port (group of 8, 16 or 32 bits). Whenever one of those bits is toggled (hint: XOR function!) you know there is a "request" and you can handle this request by setting some other digital outputs…

Can we have to use case statements for all this in FPGA VI

Yes, sure.

or some other way ??

You can use many other functions and structures in a FPGA VI, even FIFOs (aka queues)…

Re: How to do arbitration in LabVIEW FPGA

vicky2889 — Wed, 09 May 2018 08:51:56 GMT

yes by using XOR gate we will find there is request but how we determine which request we receive first.

Re: How to do arbitration in LabVIEW FPGA

GerdW — Wed, 09 May 2018 09:15:49 GMT

Hi vicky,

by default the FPGA executes loops at 40MHz - or 25ns between iterations. Do you really expect more than one request in this short interval?

I assume there will be only one request per 25ns interval so you know which request occured in which iteration of your receiver loop…

Re: How to do arbitration in LabVIEW FPGA

wiebe@CARYA — Wed, 09 May 2018 09:17:46 GMT

@vicky2889 wrote:

yes by using XOR gate we will find there is request but how we determine which request we receive first.

Set a flag, enqueuer an element, execute a case, output a value, store the timestamp, trigger an SRQ... Thousand ways to do it.

Recommending one of them is not easy, as what makes the right choice it's highly circumstantial. E.g. it depends... On an FPGA everything usually needs to fit like a glove. Each choice made needs to fit other parts.

I am pretty sure arbitration is not required to solve the problem.

Re: How to do arbitration in LabVIEW FPGA

vicky2889 — Wed, 09 May 2018 09:21:13 GMT

yes you are right. but then also how we determine which device request we receive first.

Can you please give me a small example by taking two or three inputs and then how we determine which one we receive first?

Re: How to do arbitration in LabVIEW FPGA

vicky2889 — Wed, 09 May 2018 09:23:42 GMT

Can you please give some example by taking two or three input and then how we determine which one we receive first ?

like by taking case statement

Re: How to do arbitration in LabVIEW FPGA

GerdW — Wed, 09 May 2018 09:29:17 GMT

Hi vicky,

using standard LabVIEW it looks like this:

In the FPGA you may do the ArraySearch "manually" using your own routine…

how we determine which device request we receive first.

That "first" request is the one, where the boolean value changed in an earlier iteration then the "second" one…

You need to take into account the loop iterations between the comparison of your digital inputs!

Re: How to do arbitration in LabVIEW FPGA

wiebe@CARYA — Wed, 09 May 2018 09:44:11 GMT

Or detect going up:

Re: How to do arbitration in LabVIEW FPGA

vicky2889 — Thu, 10 May 2018 03:00:17 GMT

can you please tell where i can find the highlighted part in the picture attached

Re: How to do arbitration in LabVIEW FPGA

GerdW — Thu, 10 May 2018 18:42:23 GMT

Hi vicky,

both our suggestions are actually snippets! You can download those images and drag&drop them into the block diagram of a VI to get their contents…

You are looking for a feedback node. You really should take the beginner courses!