Friday, 1 January 2016

Overriding a video mode for a specific monitor with a Raspberry Pi

I have a Raspberry Pi I use for fiddling about.  It has an odd little 10.4" Lilliput monitor with an 800x600 native resolution and a variety of inputs, including both HDMI and DVI:

  • If I use the DVI input, it reports a DMT (Display Monitor Timings - computer monitor type) with 800x600
  • If I use the HDMI input, it reports a CEA (Consumer Electronics Association - TV type) with a preferred resolution of 1280x720

I prefer to use the HDMI input as the cable is thinner and easier to connect (especially important with something as light as the Pi).  However, when I do, the Pi picks a rather blurry 1280x720.

I can force this in /boot/config.txt with the following lines:
# set DMT mode
# set 800x600 @ 60Hz
However, this is annoying if I plug the Pi into a different screen.  It is possible to force a specific mode only when a particular monitor is connected.

First, find out the display ID:
pi@mincepi ~ $ tvservice -n
Then edit config.txt to add a section in square brackets to override it:
The trailing [all] is to specify that the following lines apply to all monitor types and is just a safe thing to put in case some additional directives are applied below it.

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