[mythtv-users] Trouble with two HD-PVRs on one system

David Engel david at istwok.net
Thu Nov 12 00:06:30 UTC 2009

On Mon, Nov 09, 2009 at 06:04:27PM -0600, David Engel wrote:
> I'm going to try other cabling combinations tomorrow to see if I can
> figure out what's going on.  At this point, I think the leasting cause
> is that my system is just cursed! :)

Cursed is still in the running, but this is looking more and more like
it's probably a motherboard and/or host controller problem.

First, having both HD-PVRs connected through an external hub to my
development system works fine.  Good.  It should work with my
production backend then too, so back to it.

Much trial and error revealed that the HD-PVRs will not flake out
unless one is connected to the back panel and the other is connected
to the front panel.  Connecting both with or without an external hub
to either the back panel or the front panel results in flakiness.

It turns out my motherboard has two EHCI controllers.  One handles the
back panel ports and the other handles the internal/front panel ports.
Further testing showed having any other high speed USB device attached
to the same controller as an HD-PVR will cause problems.  For example,
accessing a USB flash drive will cause the HD-PVR to flake out.
Strangely, the HD-PVR activity does not seem to affect the flash
drive.  Is it possible the HD-PVR driver is too sensitive to
contention on the bus?

Anyway, the motherboard is a Biostar TA790GXB A2+ with an ATI
SB700/SB800 south bridge.  I tried searching for USB problems with for
that board and chipset and nothing like mine came up.  Does anyone
know of some low-level USB or PCI settings that might be worth

David Engel
david at istwok.net

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