[rescue] 1920x1080 on LCD with a TGX+ :-) (was: Re: FB resolution in PROM)

Romain Dolbeau romain at dolbeau.org
Sat Nov 7 15:03:58 CST 2015

2015-11-04 15:31 GMT+01:00 Romain Dolbeau <romain at dolbeau.org>:

> Since it seems LCD capable of handling the FFB output @ 1920x1080 or
> 1920x1200 are either non-existent or very expensive, I've decided to see if
> it was possible to fix the output instead (inspired by Mouse for an SX,
> comment quoted below).

Still no idea how to change the video settings of a FFB or a SX, but since
it's documented for the TurboGX(+), I figured I'd give it a go.

The FB FAQ list a limited number of supported pixel clocks; I think 189 MHz
is also supported at least on the TGX+ (see the attribute 'oscillators' of
the device). However I couldn't leverage this clock, my monitor wouldn't
sync. Clocks not on this list would not set at all (the TGX+ falls back to
1152x900x66). If someone find a working setting with a pixel clock of 189
Mhz, please share (settings + LCD model :-)

However, by carefully tuning the settings for a 135 MHz clock, I did
actually succeed in getting a 1920x1080 setting that works with my test
monitor :-) (An Iiyama ProLite E2473HS this time).

This is the setting that works (... for me):

" 135000000,61869,54,20,222,20,1920,18,9,18,1080,COLOR,0OFFSET"

It gives 1920x1080 @ 54/55 Hz. I have a setting for 60 Hz that syncs but
the luminosity is wrong (lighter in the top 10-15% of the screen, darker
below, a bit worrying): "
135000000,67500,60,20,40,20,1920,18,9,18,1080,COLOR,0OFFSET" (the
horizontal sync pulse is way too short to be considered sane).

Somehow the "install-console" bit in the nvramrc doesn't work and I need to
"install-console" by hand at the OK prompt. Haven't figured out that one

Once booted, X retains the 1920x1080 settings and works just fine :-) Old
hardware, but it was properly design to be a bit future-proof :-) Too bad
the VGA inputs are disappearing fast...


Romain Dolbeau

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