A Rawnsley <rcomp@xxxxxxxxxxx> wrote:
By and large, the mode def files we generate use VESA timings,
but often tweaked to ensure compatibility with as many devices
as we can test. There are, unfortunately, different
implementations of the VESA standards, which can't be easily
made accessible via the RISC OS UI. For example, there are
so-called "reduced blanking" modes, which massively reduce the
"wait times" on the mode timings, and in turn reduce bandwidth.
Most monitors prefer this, but some *may* work better with
longer blanking.
Initially, I tried to use longer blanking with ARMX6 because we
had more video bandwidth to play with, but I found that it was a
double edged sword, and most test monitors seemed to like the
lower bandwidth reduced blank modes.
HINT: It is worth commenting that the MDF contains a number of
refresh rates for high resolution modes. Some of these use
different calculation methods, with the goal that different
refresh rates may work better with some monitors.
By way of example, one of our testers has a DGM 27" 2560x1440
screen. At 1080p, it worked best with the 56hz MDF mode, and at
2560x1440 the 55hz one works best (actual numbers may not be
accurate).
At 4k, full (ie. no reduced blanking) bandwidth would exceed what
we can do on i.MX6, so we have to use reduced blanking, but it
falls in line with 4k standard definitions that I've seen for
Linux online. I should, however, stress that I've only tested
on one 4k monitor, due to funds!
TVs can be a bit funny generally. Often they will only do 720p,
1080p and so on. They *may* only accept very specific timings.
I have an issue with my Pana Plasma whereby it is correctly
positioned when wired to my ARMX6 directly, but shifted if
connected via Pioneer amp/receiver.
This build of ARMX6 OS will allow you to read monitor specs via
EDID. To do this press F12 and do a *Help ScreenModes. It'll
tell you the *command needed to read EDID to an MDF. I think it
is something like *CreateModeFile SCSI::4.$
It'll write the EDID/MDF to a file with the device's name in the
folder specified.
You'd think this would be the magic bullet needed for any monitor
or device, but I've not found this to be so. Indeed, with the
DGM mentioned above, even using EDID info doesn't seem to result
in happiness, yet the (55hz) mode I mentioned produces a lovely
picture.
However, it *may* help get a bit of a handle on your TV.
One last thing - you mention KVM... the sooner you can move away
from KVMs the better. I've had several people with issues
related to KVMs (esp old KVMs) in the last few weeks, and loathe
them now even more than I already did. Screens have multiple
inputs for a reason, and unless you're prepared to regularly
drop 100ukp+ on a decent new KVM, I'd strongly advise trying to
stop relying on them. I even lost a sale of some ARMX6s because
they weren't compatible with a 1990s VGA/PS2 KVM! Sorry to
rant.
