More tea please.

High resolution with a Matrox G550

Klaus and I spent several hours on Friday getting his new monitor to work with his slightly aged graphics card. His new monitor is a Samsung 2048×1152 LCD/TFT.

The G550 specs claim that it supports this resolution through the VGA output. Unfortunately, somewhere along the line, the DDC data was being ignored. The display specs stated that it supported a pixel clock up to 157 MHz, but Xorg told us otherwise and would limit it to 140 MHz.

So the first thing to do was to get it to ignore the DDC data, as this was definitely wrong. The “NoDDC” option in xorg.conf does this:

Section "Device"
    Option "NoDDC"

After much testing of various modelines and configuration, we discovered the undocumented “ReducedBlanking” option that allows higher resolutions to be sent over VGA connections with a short blanking period between lines. Modern TFT displays support a reduced blanking interval, as they don’t have to allow time for an electron beam to move back to the other side of the screen.

This did make me wonder whether in the days of CRTs anyone had thought of alternately reversing the direction of each horizontal line supplied through a VGA cable. I think this would allow for a reduced blanking period, higher resolution or reduced pixel clock. I guess CRTs never got up to the resolutions where this was an issue.

The trick is to put this in the “Monitor” section of your xorg.conf:

Section "Monitor"
    Option    "ReducedBlanking"

This isn’t mentioned in the xorg.conf man page. It should be!

Once we’d found that option and used Erich Boleyn’s CVT Timings Program to generate the required ModeLine with a reduced blanking time, the monitor and graphics card worked fine.

The next challenge was getting a second monitor to work on DVI output of the graphics card. Unfortunately we came across a bug that would have required us to rebuild the mga driver from source. After spending many hours getting the first monitor to work, this was too much for us to bear for one day.

There is a patch in the Xorg bug tracker that will hopefully make it’s way into a release of the mga driver in the future (unfortunately I can’t remember the bug details). Then Klaus’ monitors will both work.

Posted at 3:32 pm on Monday 9th March 2009
One Comment

Formica IEEE Talk

Jeff and I are giving a presentation on the Formica robots on Tuesday evening for the University of Southampton IEEE Student Branch. We’ll be doing a live demonstration with robots. More information can be found on the UoS IEEE site.

If you’re at the University of Southampton, this should be a nice opportunity to see what sort of stuff you can get up to during your fourth year.

Posted at 9:00 am on Monday 9th March 2009
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Shed Roof Manufacture

Jeff and I spent a chunk of the weekend working on constructing our shed. I haven’t blogged about our progress for a while. Since my last update, we’ve constructed the four walls:

Shed with Walls


Yesterday we spent about 2 and a half painful hours in B&Q. Most of that time was spent in the insulation aisle trying to decide which insulation offered us the most efficient translation of money into thermal resistance. (Yes! Our shed will be insulated :-) This took ages because all the products provide different statistics on how good they are at insulating. The means to understand or convert between these values were not available to us. We asked a B&Q employee, but he was more interested in telling us that there was some insulation available for half-price.

We eventually resolved the issue after Jeff found the datasheet for one of the products with his iPhone, allowing us to compare it against another.

Saturday then dissolved into other non-shed related things.


We’d also bought some other bits and pieces at B&Q, including some OSB and roofing felt. As soon as we started moving tools outside, it started raining. Of course by the time we’d finished repairing and putting up the awning, it had stopped raining.

We had to leave the protection offered by our awning to assemble the roof frame further down the garden. Five minutes after we’d started work on the patio, it was raining hard. A couple of minutes later, it was hailing. I think Joe took a video of us cursing about the rain from my window.

The hail stopped after a few more minutes and we spent the next couple of hours fitting the studwork into the frame. Then we began adding the OSB that will form the top of the roof:

Shed Roof Construction

It then got dark. We went through the familiar rigmarole of getting a light out and deploying the extension lead from the house. More rain. Wet sawdust is not nice! Our roof now has the outer layer of OSB on it. Unfortunately I have no pictures of this, as we were trying to get out of the rain.

Hopefully we’ll get the roof up in our next episode of construction. After that it’s the exterior cladding. It’ll be really good once that’s on, as it’ll feel like we’re really in a shed!

Posted at 2:55 am on Monday 9th March 2009

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