How does RISC OS decide screen mode?

I'm using RISC OS on a collection of rPis with assorted monitors. Some
of the monitors use composite video.
When the standard distro starts, RISC OS comes up in 1920x1080. On the
7 inch TV, this results in buttons appri=oximately 0.3 mm high, which
are quite hard to hit. Changing the screen mode is, at best, fiddly.
Am I right in assuming that the composite video doesn't support EDID,
or anything like it, so the initial resolution (during boot) is set
solely by config.txt?
Am I right in assuming that the Auto MDF somehow picks up this
information to set the RO screen?
If I force a low res mode in config.txt, can I then use a hi-res mode
Can I set up config.txt so it uses EDID if available, and if not,
defaults to low res?
Since the monitors I'm using vary from 19 inch to 7 inch, some VGA via
HDMI adapeters, some composite, and I'd like to have an SD card image
I can clone to any of them, the screen res issue is complicating
Any suggestions as to how I address this?
Alan Adams, from Northamptonshire 
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Alan Adams
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There are two modes: The mode the GPU runs, which is set by EDID or config.txt The mode RISC OS uses for its framebuffer, which you can change with the DisplayManager in the usual way The RISC OS mode is scaled to the GPU's size, and output out of HDMI or composite.
If you're using composite there's no EDID so config.txt will set the mode.
RISC OS can change the GPU mode, but I don't know the circumstances it does.
You set two modes in config.txt, one for HDMI and one for composite. I think the HDMI mode should use EDID. If no HDMI is detected then it should use the composite settings. The RISC OS mode is independent (as far as I know, though I don't know the full details).
Reply to
Theo Markettos

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