[ubuntu-uk] Screen resolution problems on dual-monitor setup

Jim Price d1version at hotmail.com
Wed Aug 10 17:41:03 UTC 2011

I think something is up with the attributions here - thunderbird and 
gmane are telling me this post is from Liam, but I think it may have 
been said by some combination of Liam and James, or just James:

On 10/08/11 15:13, Liam Proven wrote:
> On 10 August 2011 14:37, James Morrissey<morrissey.james1 at gmail.com>  wrote:
>> - - Do you know if the spec of your Radeon 200m supports these
>> resolutions combined? I would guess it does, but I'm not sure without
>> googling it. Do you know if it uses its own memory or shares system
>> memory, and if so, how much?
> - - - I am not sure, i came up with the following
> http://www.amd.com/uk/products/notebook/chipsets/radeon-xpress-200M/Pages/ati-radeon-express-200m-amd-specs.aspx,
> but don't know how to interpret most of it. Do you know if the
> information you need is on this page.

I've had a chance to google now - it rather depends on how the 
manufacturer implements the chipset. It supports sharing system memory 
and its own memory as an option by the look of it. If it is using shared 
memory, there should be a setting in the BIOS to set how much it gets.

>> Try changing resolution on one of the monitors in
>> ~/.config/monitors.xml, which is where i got the unity dock to only
>> show on the primary monitor.
>> Here, after i saved the changes to ~/.config/monitors.xml, and logged
>> out, i got an error message saying �that the resolution would not work
>> as i logged in.
>> - -What was the exact error message you got?
> - - - When i first did this and got the error message, i had only
> changed the resolution on the laptop (to 1280x800). When i changed the
> resolution of both of these i got no error message. Instead i ended up
> with the same problem as i had when following step 4 from my last
> email: screen smear (images would remain in the screen after things
> had closed, or leave remnants when i dragged windows across the
> screen).

It may have been an error to do with trying to get it to clone monitors 
at different resolutions - that just wouldn't work.

>> - -Can you post the monitors.conf you have at the moment?
> - - - Which file exactly do you need for my monitors.conf.

Sorry, typo alert. I should have typed monitors.xml but I was thinking 

> The
> ~/.config/monitors.xml, looks like this at the moment:
<snip config.xml for brevity>
>> - - First I need to know what version of Ubuntu you are running, as
>> there are differences between them, and I like to post stuff which I
>> can test in the same environment before I post it.
> - - - Natty 11.04

That's good - as I remember xrandr works pretty well in Natty.

>> - - You also need to decide which of the two windows is going to have
>> the (I assume) Gnome menus on it
> - - - I initially had this problem, but found a blog post telling me
> to edit �~/.config/monitors.xml. In that file i changed
> "<primary>no</primary>" to �"<primary>yes</primary>" in order to get
> the unity dock on the laptop monitor ("LVDS"), making it the primary
> monitor. Now the Gnome menus seem to work. i get the global menu
> showing only in the monitor in which the active programme is running.

The other way is to move the monitor you want to be the primary to be to 
the left of the other one in the system>preferences>monitors dialog.

> Liam Proven's blog page, just linked, describes my machine. A 6 year
> old Asus, which can no longer handle windows.

The next bit sounds like it might be attributable to Liam? Or not?

> Aha! That is interesting.
> I will say that on my old Thinkpad, to use multiple monitors at all, I
> have to drop all the screens down to 16-bit colour.
> (Either 65,535 or 32,768 colours, it makes no real difference. Most
> "16-bit colour" modes are actually 15-bit colour: 5 bits for R, G&
> B.)
> On Windows I have to do this manually, by setting both screens,
> individually, to 32K colours - *then* changing resolutions. The
> Thinkpad only has 16MB of video RAM, which limits it to 2 screens at
> 1024*768 in 24-bit colour. In  16-bit colour, I can run 1024*768 +
> 1280*1024. On Ubuntu, there is no UI for changing colour depth, so I
> use the xorg.conf file I documented in my blog.
> You might want to try this if your machine is of a similar age.

I'm thinking checking the amount of memory allocated to the graphics in 
the BIOS might be worth doing. For X to have enough memory for both 
displays at 32bit colour, you would need ~75MB, although the settings 
are likely to be in power-of-two increments, so you might need to set it 
to 128MB shared memory as the next highest setting.

> There are no proprietary ATI drivers for my "Mobility Radeon" chipset
> - it's too old.

That's what I suspected.

Can you tell us what model of laptop you have there, so I can google for 
the graphics configuration it supports?


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