Hi Rob, On Wednesday 15 October 2008, Rob Owens wrote: > Laurent Pinchart wrote: > > Hi Rob, > > > > On Wednesday 15 October 2008, Rob Owens wrote: > >> Has anybody gotten a webcam to work on an LTSP-powered thin client? I > >> asked on the LTSP list but apparently nobody there has done it before. > > > > Could you describe the problem with more details ? A quick summary of the > > hardware/software setup would probably be interesting too. > > LTSP is Linux Terminal Server Project. Basically it allows you to run > low-power, diskless workstations (also called thin clients) completely > over the network. The thin clients retrieve a basic operating system > from the LTSP server, then establish a remote session (graphical or > otherwise) to the LTSP server or to any other server you specify. > > The key here is that there is no embedded operating system on these thin > clients. They use PXE or Etherboot to get their operating system from > the LTSP server. > > The thin clients run a local X server (downloaded from the LTSP server), > and then all applications run on the LTSP server. A 200 MHz thin client > with 64 MB of RAM is capable of running modern software very quickly. > Well, really it's only displaying the software -- it's actually running > on the server. > > Anyway, this causes some complications when plugging local devices into > the thin client, because the server needs access to these devices. > Local usb storage works. Local sound works. But I haven't come across > anyone using local webcams. When I tried it, it didn't work, but I > didn't try for very long. I have to borrow the webcam to do my testing, > and I have limited time to do my testing.
Do you know how local USB storage is handled ? Obviously, as the USB storage device is plugged into the thin client, the thin client operating system (both kernel space and userspace) must support the device and somehow "export" it through the network. I see two ways this can work for USB storage devices. Either the thin client acts as a USB-Ethernet bridge (USB/IP), with the server handling the actual USB mass storage protocol, or the thin client mounts the device locally and exports it through the network (NFS, CIFS, ...). In the first case the same system might be used for webcams, although the latency and bandwidth requirements are quite different. > So the problem can be attacked in a few ways. All of these depend on > getting the proper modules to load when the camera device is plugged in, > which I think I can handle. > > 1) Run the video application (luvcview, for instance) locally on the > thin client. LTSP calls this "local applications" and I'd consult the > LTSP list for instructions on doing that. That's probably the easiest path for you, although it might be a bit heavy on the thin client resources. > 2) Run the video application on the server (the normal way LTSP works), > but convince the video application to access a video device over the > network. You will need a server process on the thin client to forward the video stream to the server-side application, which will then re-forward them to the thin client's display. The CPU and memory constraints incurred by the Linux UVC driver would still have to be handled by the thin client as in option 1, but you will save the application's memory and CPU footprint. In case of simple applications such as luvcview I think this will actually be slower than option 1. > 3) Have LTSP treat the local webcam the same way a local USB drive or a > local sound card is treated. Unfortunately I don't know the specifics > of that, so I was hoping to hear from somebody "sure I've done that > before, it's easy!" Can you ssh into the LTSP box ? If so you can easily check if USB mass storage devices are locally mounted or exported through the network using USB/IP. > Thanks for any advice you guys might have. > > By the way, I'm trying to use the ProScope HR camera at the 9 thin > clients that are installed in my company's machine shop. The cameras > are to be used for inspection of some very small parts. This camera > does work on Linux using the uvc driver. Best regards, Laurent Pinchart _______________________________________________ Linux-uvc-devel mailing list [email protected] https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
