[mythtv-users] IMON LCD backlight

Ronald Frazier ron at ronfrazier.net
Thu Dec 10 04:41:56 UTC 2009

On Wed, Dec 9, 2009 at 11:01 PM, Jarod Wilson <jarod at wilsonet.com> wrote:
> For some reason, this currently seems to be broken, and nobody has come up with a
>fix yet. The lcdproc daemon can be configured to turn the display off, and it does turn it
>off for a bit during shutdown, but the display lights back up as soon as the box finishes
> powering off... So far as I know, we send the exact same display off packet sequence
>as windows does, so I can't really explain it. My best guess is that maybe the imon driver
>needs to be unloaded cleanly (modprobe -r), sending those display off commands in its
>module_exit() routine, and then maybe it'll stay off, but its just a WAG. Not high on my
>priority list to poke at it though, but I'd welcome any assistance in determining root cause
>and a fix.

It's been a few years since I did my initial experiments with the LCD,
so I hope my memory is correct.

As I recall, you are correct that we do send the same data as windows
does. When I was testing, I did both monitoring from the windows side
using usb snoopy, and I installed windows in a virtualbox instance
running under linux and monitored what usb commands got passed through
to the hardware. I couldn't find any sort of command that we aren't
passing properly.

As far as your modprobe comment, I don't think that's it. I
experimented with writing a userspace driver for the device using
libusb and I got the same results. It seems unlikely to get the same
problem through 2 different interfaces, so I suspect it's something
lower level. My WAG has always been something like linux issuing a USB
bus reset on poweroff.

Anyway, it's annoying, but I learned to live with it....mostly because
my machine does suspend-to-ram, and for that the LCD actually stays

Disclaimer: none of this is very fresh in my memory, so I hope I
didn't say something that was inaccurate. Also, I'm not a very
experience driver writer, so it's possible I completely screwed up in
my testing/debugging methodology. Take that for what it's worth.

Ronald Frazier Photography - http://www.ronfphoto.com/
Blogging About Photography - http://ronfrazier.blogspot.com/

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