[Open-graphics] bootstrapping the video mode

[Timothy Miller]

On 8/4/06, James Richard Tyrer <tyrerj at acm.org> wrote:
> Dieter wrote:
> > somebody wrote:
> >> It almost sounds like what you're asking for is the ability to watch
> >> the 80x25 text framebuffer, scan it periodically for changes, and then
> >> send that out via serial using vt100 codes so as to replicate what one
> >> would see on the VGA screen.
> >
> > If that is the easiest way for OGC to do it, it sounds like that would work.
>
> This should be straight forward and you can use it for both the
> character modes and the graphics modes (which still allow Video BIOS
> calls to write text to the screen).

Well, let's get to work on that nanocontroller, because that's the
only way we're going to get this.

>
> You have a character buffer for 132 X 60 characters (and attributes).  A
> DMA controller constantly reads it (raster scan).  The read character
> codes go to a character generator in RAM which outputs the video data to
> add to the attributes and this data is written to the screen frame
> buffer.  You could probably speed this up by having a 'dirty' flag for
> each character so that ones that hadn't changed since the last read
> would be skipped.

I'm not sure where to put the dirty flag.  Probably, what we'll do is
just have a shadow copy of the framebuffer as it was last updated.
Every update loop, we'll see what characters changed between not and
the last update and just send the appropriate VT100 codes.