Maximal number of trackers

[Johan Fogelström]

Johan from Bream IO here (We are well known to Tobii at this point)

We have a sort of special use case with eye trackers and connect multiple trackers to the same computer. We soon need to be able to connect ten trackers simultaneously.

But there is a constant in the Gaze SDK C API called Max Devices that is set to 9.
How would we go about to enable 10 devices? Recompilation of SDK? Custom driver? Or is it just a misunderstanding of the constant?

I do not currently have 10 trackers to test with, which is why I ask this question instead of simply testing, and will not until shortly before needed.

[Anders]

Hi Johan,
I’ll have to do some research to find the answer to your question — be right back.

In the mean time: how many trackers do you think your application will require at most? Will ten be enough or will it be eighteen (or whatever) next fall?

Would it be feasible to use more than one computer?

[Johan Fogelström]

Since my posting, I have been in contact with one of the developers regarding this.
The answer I got was that it is really a limit of seven and the changes necessary was not trivial.

We do not think eighteen will ever be needed. The management of hardware (not to mention the limitations of USB ports) would put a stop to that. If more than 10 is ever involved, it will be possible to naturally split them up into groups dealt separately.

It would be feasible to use more than one computer, but not one per tracker.

[Anders]

Hi Johan,
it’s good to hear that you already found out 🙂

Yes, there is currently a limit of seven USB-HID trackers on the same machine. The limit comes from a design choice to only use a single page of memory for the tracker metadata. We anticipate that the limitation will be removed sometime in the future but it’s hard to tell when that will be.

So I hope that a solution with, say, two computers, each hosting five trackers, can be viable for now.

[Author]

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