A pair of small Linux system reviews [LWN.net]

One simple question

Posted Dec 10, 2007 9:34 UTC (Mon) by tialaramex (subscriber, #21167) [Link]

What is it that you need DVI for? Do you have a DVI-D only flat panel that you were hoping to
connect ? I suspect such panels are a bad investment, DVI-D doesn't have the performance to be
as long-lived as VGA's analog RGB was, it already looks strained at today's resolutions. If
you just need a DVI connector and not DVI-D protocol then a $0.50 passive converter is much
cheaper than a Mac Mini.

One simple question

Posted Dec 10, 2007 15:17 UTC (Mon) by alankila (subscriber, #47141) [Link]

My experience with DVI compared to VGA is that DVI produces noticeably crisper picture. It's
important especially for text, where contrast seems better with DVI. (It's easy to understand
that two unnecessary conversions in the signal path are not good for picture quality.) That
alone is surely worth something.

Second, related matter is that the flat panels I have been using tend to get fuzzier with time
and need a resync once in a while. I do not know why this happens, but it's an annoying extra
bother. It's often required when I get to work on monday, for some reason.

Situation is not so simple, but...

Posted Dec 10, 2007 15:26 UTC (Mon) by khim (subscriber, #9252) [Link]

It IS possible to produce crisp picture with VGA if you are using good video card (from Matrox, for example) and LCD panel with very good ADC. But cheap models are almost always unusable and in reality I'm yet to see onboard video with VGA connector I can tolerate. So I gave up trying and just refuse to use anything with analog video connection...

Situation is not so simple, but...

Posted Dec 13, 2007 9:57 UTC (Thu) by zdzichu (subscriber, #17118) [Link]

And a good cable. I have Matrox card and VGA only LCD. With good cable (1cm thick, filters on
both ends) image on LCD is crisp. With cheap cables bundled with some videocards/LCDs (thin,
about 4mm diameter, one or no filters) image is blurred.

One simple question

Posted Dec 11, 2007 0:57 UTC (Tue) by endecotp (guest, #36428) [Link]

> My experience with DVI compared to VGA is that DVI produces 
> noticeably crisper picture.

This should only become an issue at higher pixel rates.  These "mini" systems have relatively
low maximum resolutions, so it shouldn't be much of an issue.  I think that both of the ones
in this story use an AMD Geode which could only manage 1280x1024 last time I looked.  The
VIA-based boards can get up to 1600x1200 (and a few have DVI).

If you're seeing non-crisp images at lowish resolutions (say 1280x1024 or below), something's
broken.  Maybe a crap cable or wonky connector?  Maybe your X server has chosen a
high-frame-rate mode, e.g. 120 Hz?

My experience - and I have spent some time working with the ADCs that LCD monitors use - is
that unless you're unlucky analogue works OK at 1600x1200@60Hz, but you wouldn't want to go
higher than that.

One simple question

Posted Dec 11, 2007 2:07 UTC (Tue) by zlynx (subscriber, #2285) [Link]

I've got a pretty nice ViewSonic VX900 at home and I use the analog port to connect to a
Belkin KVM for a few servers.  The desktop machine uses the DVI.

The analog display really is crap, even at server resolutions of 800x600.

Every time I switch machines on the KVM the sync changes.  Even stopping X and restarting it
on the same machine (which does a resolution switch from console and back) makes it lose sync.
The alternating pixel gray X start screen is horribly fuzzy until I re-run the analog
auto-adjust.

VGA has always been a very silly idea for LCD.  Digital to analog to digital?  What is this,
display over a modem?

One simple question

Posted Dec 16, 2007 0:00 UTC (Sun) by endecotp (guest, #36428) [Link]

> analog port to connect to a Belkin KVM ... is crap

The KVM is almost certainly the problem.  Maybe you also have long cables?

> Every time I switch machines on the KVM the sync changes.

You might like to investigate some other brands of KVM gear.  To some extent, you get what you
pay for.

Disclaimer: I have worked for one of Belkin's KVM competitors.

One simple question

Posted Dec 16, 2007 21:35 UTC (Sun) by zlynx (subscriber, #2285) [Link]

I do not think the KVM is the problem.  It always worked well with a CRT display and the LCD
loses perfect sync even when switching from 800x600 to text console then back to 800x600.

It could be the video card, it could be the cables, it could be the LCD.  

But the point is that DVI does not have any of those problems because it is much less
complicated to do digital->digital->digital than digital->analog->digital.

Something is broken ? Of course !

Posted Dec 11, 2007 7:58 UTC (Tue) by khim (subscriber, #9252) [Link]

If you're seeing non-crisp images at lowish resolutions (say 1280x1024 or below), something's broken.

Yum. But unfortunately for small systems with high-density boards in these conditions more often then not in these conditions "something" is analog path of video signal on the board itself.

Plus constant problems with sync, etc. No, the VGA is very bad idea for LCDs...

Something is broken ? Of course !

Posted Dec 20, 2007 12:31 UTC (Thu) by endecotp (guest, #36428) [Link]

> for small systems with high-density boards in these conditions more often
> then not in these conditions "something" is analog path of video signal on
> the board itself.

This would also be true for DVI signals, where careful routing of the LVDS pairs from the
transmitter chip to the connector is needed.

If you want to CONNECT LCD monitor - you don't need DVI, if you want to USE it - you do

Posted Dec 10, 2007 15:21 UTC (Mon) by khim (subscriber, #9252) [Link]

Sorry, but the LCD must be connected via DVI to be usable - at least for me. I can work with LCD all day if it's connected via DVI, but only 4-5 hours before headache strikes if it's connected via VGA...

Right now I'm seein the LWN on HP's LP3065 connected via DVI (2560x1600) so I can assure you DVI is not yet at the end of it's life...

If you want to CONNECT LCD monitor - you don't need DVI, if you want to USE it - you do

Posted Dec 10, 2007 17:55 UTC (Mon) by alankila (subscriber, #47141) [Link]

You apparently have practical experience on dual-link DVI things. Will it work on Linux? What
graphics hardware do you have?

Dual-link DVI ? No FLOSS solutions at this time

Posted Dec 10, 2007 20:01 UTC (Mon) by khim (subscriber, #9252) [Link]

I'm using some Quadro FX card (lspci shows Quadro FX 3450) and it works "out of the box" (via DPMS) with nVidia drivers (I think I had trouble with "nv" drivers). Hopefully AMD (with community help) will have a compatible 100% FLOSS solution soon, but when the system was assembled we had no such promises and nVidia is less flacky...

Quite stable on this 64-bit box but as usual with binary drivers YMMV...

Some notes

Posted Dec 10, 2007 20:15 UTC (Mon) by khim (subscriber, #9252) [Link]

Dual-head is supported (I don't use it, but we've tested it and it worked) and there are commented modelines in xorg.conf:
Modeline "1920x1200" 155.0 1920 1984 2016 2144 1200 1203 1206 1212
Modeline "2560x1600" 348.16 2560 2752 3032 3504 1600 1601 1604 1656 -HSync +Vsync
Latest version of nVidia driver works just fine via just DPMS but apparently some older versions don't...

If you want to CONNECT LCD monitor - you don't need DVI, if you want to USE it - you do

Posted Dec 13, 2007 11:11 UTC (Thu) by job (subscriber, #670) [Link]

Why wouldn't it work? Dual-link DVI is a signalling standard so it's completely on the
hardware side. Linux doesn't know anything about what kind of transport the signal uses just
like it doesn't know what colour the cable is. (Perhaps you could ask the monitor using some
PnP magic, but I'm not sure even the monitor knows single-link from dual-link DVI.)

DVI dual link

Posted Dec 13, 2007 18:29 UTC (Thu) by tialaramex (subscriber, #21167) [Link]

Modern graphics chipsets may actually expect the driver to set this stuff up.

It might be as simple as flipping a bit, or it may be more complicated. There might be a
provided firmware controlled part of the chip which does it for you, or there might not. As
far as I remember there was a distinct piece of work for supporting things like dual-link in
the radeonhd driver.

So yes, Linux (or rather, the X driver) does know what sort of transport is being used, and
indeed for some types of hardware it knows the type of connector (this information is in a
firmware lookup table e.g. for the various DVI-like connectors) used, how the user is supposed
to use it (USB's HID standard specifies things like "thumb control" even though obviously a
hardware driver doesn't per se need to know that level of detail) even the color (Intel's HDA
tells you this, though it's not always very accurate)

The monitor definitely knows the difference, a display isn't required to implement dual-link
DVI if it doesn't need it and so they don't. The pins for the second TMDS link can be omitted
from the design altogether.

One simple question

Posted Dec 10, 2007 19:00 UTC (Mon) by leoc (subscriber, #39773) [Link]

There are all sorts of mATX and Via boards that support DVI (sometimes with an optional addon daughter card), so you could pick a small case and throw one of those in there to build your own small system with DVI. There are web sites like mini-box.com and logicsupply.com that specialize in this type of system. You can even buy them fully assembled so you don't have to do it yourself.

What is the problem?

Posted Dec 11, 2007 11:04 UTC (Tue) by man_ls (subscriber, #15091) [Link]

The Mac Mini makes a very nice Linux box. Mine (first generation PowerPC) runs Debian like a charm; only problem is that I haven't got around to make it sleep properly, but with a boot time of under a minute it is not such a hassle.

The only problem is that it is a bit pricey.

What is the problem?

Posted Dec 12, 2007 10:50 UTC (Wed) by Los__D (subscriber, #15263) [Link]

- And (AFAIK) with a power usage quite a bit higher than the low power systems presented
here...

What is the problem?

Posted Dec 12, 2007 11:25 UTC (Wed) by man_ls (subscriber, #15091) [Link]

True, mine uses from 32 to 85 W, and the newer ones little less. Still it is a far cry from the ~100 W (idle) for the typical tower.

What is the problem?

Posted Dec 22, 2007 15:02 UTC (Sat) by anton (guest, #25547) [Link]

The page you linked claims that the newer ones use more when loaded. I would expect that the PowerPC-based Mac mini uses about as much as my iBook G4 (1066MHz) with the screen light turned off, i.e., 12W-22W; maybe a little more, because the CPU is a little faster, but not as much as the page claims.

Concerning typical towers, 100W idle may be right, but if you are interested in energy efficiency, you can easily build one that takes less than 60W idle; a friend of mine recently built one that consumes slightly over 50W when idle: An Asrock board with the Nvidia 6150 chipset (with integrated graphics), an Athlon 64 X2 5600, 4GB RAM, and some drives were the main components.