Turbo USB and USB woes

[cyrille.de.brebisson]

Hello,

I have just reworked the setup that we use at the club.
We have 4 caméras,
2 planetary the electronic finder (ASI178) and the guiding scope (ASI585),
2 main ones on the scope (ASI2600) and the side mounted wide angle refractor (ASI1600).

These all go through a single USB3.2 hub to the main PC.

I have only tested, at this point in time, with the 2 planetary, and I seem to see frame limiting (2 sharpcap instances, one per camera)
I can boost a single camera to "turbo USB" 100 and get it's nominal framerate, but then the other camera drops all frames...

Now, we will most likely never be shooting full frame rate on all 4 camers, this was a stress test, however, it looked as if they was some issue, not caused by the USB speed as the USB3.2 has a data throughput way above what a single camera can send...

Any idea as to how to handle that?

We will be participating in a moon gemenids impact shootout" in 2 weeks from now and we will be trying to get 25fps from our 2 primary caméras, so we need this to work

Note, I checked and the limitation did not see to be caused by the CPU.

Thanks for the help.
Cyrille

[turfpit]

Cyril’s

Is the USB hub mains powered?

Dave

[admin]

Hi,

I am suspicious that this will never work properly, regardly of how fast the link from the hub to the PC is. The thing is, to maintain full frame rate on a USB3 camera, it needs to be sending data over the USB link basically all the time (or very nearly). While the hub may have some small internal buffers to hold data ready to be sent on to the PC, I suspect they are really rather small, and if the main link happens to be busy at one point in time, it may stall the flow of data from the camera as the hub cannot accept it. It might (just possibly) be that a 'better' hub might do a better job (back in the days of USB2 and 1.1 hubs, some hubs were 'multi TT' and could cope better with multiple USB 1.1 devices sending data at the same time - I don't think multi-TT applies in the USB3/3.1/3.2 world, but something similar could).

Anyway, I would recommend individual cables straight back to the PC for each high speed camera (if necessary for cable length, put a hub/active extension cable in to each). You will also probably get away with a single camera for high speed work and a few simple devices (filter wheel, focuser, etc) on the same hub.

cheers,

Robin

[cyrille.de.brebisson]

Hello,

Powered hub.
As far as I can tell, these 3000*2000 pixel and some change cameras will send frames that are somewhere under 20M/ frame (around 12 for the 178 and 16 for the 585 from memory).
So at 30 to 40 fps (max speed), this would b
12*30 (178) + 16*40 (585) = 360 + 640 MB/s = 1GB/s.
1G/s is max USB 3.1 speed and around 1/2 the speed of a USB 3.2 hub.

So, "in théory", it should work
In practice, the strange thing is that one camera has 100% frame drop and the other one has no drops... it is strange that they do not "share"...

Anyhow, I will double check what I can see on the system next time I go at the club.

About dual USB links, the problem is that they are nearly 7m between the telescope and the PC so multi USB with repeaters gets expensive!

Thanks for the usual extra quick answer!
Cyrille