[Server-devel] [XSCE] CentOS 7 quirk: VGA cable not re-attachable

[Adam Holt]

On Mon, Aug 29, 2016 at 8:16 PM, George Hunt <georgejhunt at gmail.com> wrote:

> I do most of my testing of real hardware, and came across the VGA problem
> also,  I've migrated to using the hdmi input to my monitor, and dongles
> that translate to hdmi.  And I'm able to swap the monitor cable
> indiscriminately
>

Cool to have that affirmative result: even if we learned in Bellingham, WA
(LinuxFest Northwest) late April that HDMI also needs to be inserted during
NUC bootup (often? always? sometimes? anyway demonstrated by Tom Gilliard's
main NUC 4 months ago!)

For those of us living in the dark-ages-of-VGA (thru no choice of our own,
funds are limited ;) here a few (final?) concrete tips/results on this
fragile CentOS support for VGA: (compared to Fedora 22 etc)

- 4 Different Screens were tested (4 diff manufacturers, some genuinely
modern) and the result is essentially the same in all 4 cases: VGA video
rarely if ever re-appears if your VGA cable (or Mini DisplayPort adapter
cable) is disconnected after boot, no matter how briefly?

- Fun Curiosity: you can reliably pull the power cable out of the LCD
screen (or power cycle the LCD monitor with its own ON/OFF button) and VGA
video *will* quite survive amazingly, promptly re-appearing on screen,
anytime later when the monitor's power (or power cord) restores electricity!

- Bonus Trivia: if the VGA cable is disturbed/disconnected-then-reconnected
while the monitor's off, video will NOT subsequently re-appear when the
monitor is later powered on.  How on earth "God Knows" that the video cable
was briefly disconnected-then-reconnected to the monitor while the monitor
itself was off, I have no absolutely no clue..but then again I don't know
enough about the VGA protocol to attribute this entirely to Voodoo ;-)

.On Mon, Aug 29, 2016 at 3:59 PM, Adam Holt <holt at laptop.org> wrote:
>
>> On Mon, Aug 29, 2016 at 5:50 PM, James Cameron <quozl at laptop.org> wrote:
>>
>>> Only tested one monitor?  Try another; the EDID communication path
>>> over VGA could have problems, or the data in monitor Flash unusual.
>>>
>>
>> I tried a different brand of LCD monitor, and the problem remains:
>>
>> Fedora 22 NUC allows re-attaching of the VGA cable every time, whereas
>> both CentOS NUC's are highly intermittent (the VGA cable fails to show any
>> video upon re-attachment, the vast majority of the time).
>>
>> In hindsight, the other LCD monitor (tested across all 3 NUC's) behaves
>> very much the same way.  Perhaps 10% of the time (or less) video
>> re-appears, sometimes triggered by starting/leaving X Windows using
>> Ctrl-Alt-F1 or Ctrl-Alt-F2 (or running "reboot" from ssh, on any machine
>> that was running X Windows at the time, causing video to suddenly re-appear
>> during the shutdown process) but regrettably on both CentOS 7 NUC's
>> (NUC6i3SYH & D34010WYKH) I haven't found any repeatable pattern that
>> permits video to be usefully restored (without a full reboot!)
>>
>> PS Problem occurs independent of CentOS 7 NUC's that are running X
>> Windows and those that are not.  I mention X Windows only because leaving X
>> / re-entering X seems to (sometimes) facilitate recovery of the video
>> signal in certain not-quite-repeatable situations.
>>
>> Also check age of monitor.  Mix not old and new wineskins.
>>>
>>
>> The earlier test monitor's from the prior decade it's true, but this
>> newer test from a much more recent vintage ;)
>>
>> --
>>> James Cameron
>>> http://quozl.netrek.org/
>>> _______________________________________________
>>> Server-devel mailing list
>>> Server-devel at lists.laptop.org
>>> http://lists.laptop.org/listinfo/server-devel
>>>
>>> --
>>> <http://lists.laptop.org/listinfo/server-devel>
>>> Unsung Heroes of OLPC, interviewed live @
>>> <http://lists.laptop.org/listinfo/server-devel>http://unleashkids.org !
>>>
>>
>


-- 
Unsung Heroes of OLPC, interviewed live @ http://unleashkids.org !
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