Date   : Thu, 02 Jan 2014 15:07:27 +0100
From   : kortink@... (John Kortink)
Subject: Modernisations

On Thu, 02 Jan 2014 12:08:59 +0000, Phil Blundell <philb@...>
wrote:

>[...]
>
>It probably wouldn't be all that hard to make a daughtercard to replace
>the video ULA and provide an HDMI or DVI output directly.  You could
>probably do that without introducing any appreciable output lag and I
>imagine the resulting video quality would be a bit better.

If only it was that simple.

First of all, the video ULA does not get all the signals that
are needed to do this, e.g. hsync, vsync, and the TTX pixel
clock (although it may be possible to derive it, since it
comes from the same source as the video ULA pixel clock).

Second, HDMI and DVI do not tolerate interlacing, nor the
(low) line and frame rates that are generated, which can
only be solved by buffering and then rendering at two or
four times the normal rate(s).

Which makes for a rather non-trivial piece of hardware.
Even more so when you also want to add smart adaptation
to the native resolutions of monitors (e.g. to avoid
scaling by non-integer factors, or maintaining aspect
ratio).


John Kortink