[linux-dvb] Multiple em28xx devices

Markus Rechberger mrechberger at gmail.com
Thu Apr 9 16:31:14 CEST 2009


On Thu, Apr 9, 2009 at 4:05 PM, rvf16 <rvf16 at yahoo.gr> wrote:
> Hello.
>
> I am trying to use two Terratec Cinergy Hybrid T USB XS FM tuners, at
> the same time, on the same system.
> Both work great when used solely.
> When used simultaneously the second one gives the following error :
>
> v4l2: unable to open '/dev/video1': No space left on device
>
> I am using the em28xx-new-b2e841c05e94 driver from
> http://mcentral.de/hg/~mrec/em28xx-new on a Fedora 6 system.
> I have opened this topic in the em28xx mailing list
> http://mcentral.de/pipermail/em28xx/ but it seems it is not maintained
> any more.
>

hmm I'll check this there has been an update of the mailsystem on that
box recently.

> According to comments on relevant problems (the following is for spca5xx
> driver for cameras with same problem) :
> -----------------------
> When other USB devices are present on the same host controller bus as
> the camera, the bandwidth requirements of the spca5xx driver are not
> being met, with some hardware configurations.
> The spca5xx driver is asking for more bandwidth than is available which
> results in these error messages.
> -----------------------
>
> We are, under these circumstances, advised to either insert the device
> in another USB socket or even install a PCI card with extra USB sockets
> so that the device ends up in different bus.
> I tried to insert the second device in another usb socket but it always
> ends up at the same bus with the first one :
>
> #lsusb
> Bus 005 Device 014: ID 0ccd:0072 TerraTec Electronic GmbH
> Bus 005 Device 015: ID 0ccd:0072 TerraTec Electronic GmbH
> Bus 005 Device 001: ID 0000:0000 Bus 002 Device 006: ID 046d:c50e
> Logitech, Inc. MX-1000 Cordless Mouse Receiver
> Bus 002 Device 001: ID 0000:0000 Bus 004 Device 001: ID 0000:0000 Bus
> 003 Device 001: ID 0000:0000 Bus 001 Device 001: ID 0000:0000
> which happens to a lot of people from what i have seen.
>
> As this is a laptop with 4 USB sockets :
>
> # lspci | grep USB
> 00:1d.0 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI
> #1 (rev 01)
> 00:1d.1 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI
> #2 (rev 01)
> 00:1d.2 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI
> #3 (rev 01)
> 00:1d.3 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI
> #4 (rev 01)
> 00:1d.7 USB Controller: Intel Corporation 82801G (ICH7 Family) USB2 EHCI
> Controller (rev 01)
>
> i cannot install a PCI card with extra USB sockets so there goes
> workaround number two.
>

you can simply try to load the em28xx with alt=3

modprobe em28xx alt=3

as long as the bus is not fully utilized this should work fine!
remember you only have 480 mbit; analog TV at least requires up to 170
mbit for 1 device.

cheers,
Markus
> In spca5xx case a developer patched the driver so that the bandwidth was
> throttled in such a way that two devices used simultaneously would never
> exceed maximum.
>
> Can that be done with em28xx?
> If not, is there any other workaround to this problem?
>
> Thank you.
> Regards.
>
>
>
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