[MinnowBoard] NVRAM Issue: No Video, but UEFI not bricked

J.H. warthog19 at eaglescrag.net
Mon Feb 16 05:03:19 UTC 2015


On 02/15/2015 08:47 PM, John Roach wrote:
> Hello all. I'd like to revive this as it has been a problem this last
> week.  One day I had to re-flash my boards 3 or 4 times until I got a
> working setup.  Now when I turn off the MinnowBoard and turn them back
> on I get nothing until the Ubuntu loading screen.  Similar to what
> Hans was talking about above.  I also ran into the same symptoms as
> described in this comment
> (https://bugzilla.yoctoproject.org/show_bug.cgi?id=7027#c8).  Seems
> bug 7027 hasn't had any more activity on it, does anybody know how
> widespread this issue is or if a fix is planned?
> Cheers,

Bug 7027 is a hardware problem, contrary to Corwin's assertion in
comments #7 and #8.  The problem is primarily a lack of level shifters
on the differential pair for the HDMI signaling, and a possible issue
one the i2c lines and an existing level shifter not having the right
resistors in place to drain correctly.

(Re-)Flashing the board will not resolve this, and if it does it's
incidental and/or a different problem.  What you are describing above
(with the display only becoming visible once the OS has changed the
screen resolution) is part of this bug (most likely relating to the
resistors, but could be partially due to the level shifting on the
differential pairs).

Is this being addressed: yes, however the fix requires a new part and a
spin on the board, and there's several things all getting dealt with at
once there.  There's no ETA on when that's going to be completed and
out/available.  Since the bug is waiting on that fix to make it into
hardware, there's not much to comment on there till the new hardware is
completed.

There is a potential work around if you are having issues, however.  If
you can snag a powered hdmi switch and place it between your monitor and
the MAX this seems to generally resolve the problems, as it acts as the
level shifter and the i2c issues also seem to get dealt with.  I'll
admit it's not the most elegant fix, but everyone who's had problems and
tried it has reported success so far.

- John 'Warthog9' Hawley


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