[ ] Monday, 29 December 2014 [ ]

Sparks will fly

Christmas lectures from the Royal Institution.

2 out of 3

two screens

Only 2 monitors…
pic.twitter.com/zKRO93yAU6

— Fred Crowson (@fcbsd) December 29, 2014

Jonathan pointed out that output pipes are limited to two on Sandy bridge: 

On Mon, Dec 29, 2014 at 08:57:15PM +0000, Fred wrote:
>
> I currently have three monitors connected to my laptop but if I try to
> enable X on the third one I'm getting the following error:
>
> port:fred ~> xrandr --output VGA1 --auto
> xrandr: cannot find crtc for output VGA1

...

> vga1 at pci0 dev 2 function 0 "Intel HD Graphics 3000" rev 0x09

Sandy bridge only has two output pipes, it isn't possible
to use three outputs.  Radeon hardware tends to support more
outputs http://xorg.freedesktop.org/wiki/RadeonFeature/#index7h2

Ivy bridge supports three outputs with two of them sharing
a clock assuming the system has two displayport outputs (and none do?).
Haswell is a bit less restrictive still.

Quoting https://01.org/linuxgraphics/documentation/3-pipes

"3-pipes is a feature that allows users to have 3 Monitors plugged in.
It is present at 3rd Generation Intel Core processors with Intel
HD Graphics (codenamed IvyBridge) and 4th Generation Intel Core
processors with Intel HD Graphics (codenamed Haswell).

For other platforms only Dual outputs are supported.

IvyBridge limitations
In order to get 3 screen outputs at Ivybridge you shall use 2 Display
Ports + any display with some limitations on modes supported.

Haswell limitations
Haswell 3-pipes is less restrictive than Ivybridge. You can have 3
screns with

* 2 Display Ports + any display

* 1 Display Port and 2 HDMI or DVI

* 1 VGA and  2 HDMI or DVI

and no restrictions on mode combination."

Dave Josephsen

Interesting blog.

$Id: diary,v 1.38 2025/01/01 22:43:54 fred Exp $