On 2020-07-03 14:54, Lars Brinkhoff wrote:
Johnny Billquist wrote:
Oh, and just for the people who don't want to read a lot of
documentation, the smooth scrolling is essentially done by the
terminal by changing where the source of the video signal generation
picks up font information [...]
I hope that made sense... :-)
Thanks, I think it does.
Emulation at this level of detail really isn't that uncommon now.
I can't say that I've seen much of it anywhere. The VT100 also have a
lookup table for each line, so that scrolling can be done fast, but
which also means that the video generation needs to also go through that
table. While obviously you can always emulate anything, the emulating of
detail down to analog signals is not something you do that often, unless
there is additional reasons to. One reason being that this starts
becoming a performance problem. Many analog simlulations/emulations are
not done in realtime because of that.
But if we want to emulate a terminal, I would say that realtime
emulation of the hardware is a must.
And it's easy to just do it partially. You do have the video memory, and
for most purposes that would be good enough for the emulation to work
satisfactory, a thing like the smooth scrolling means you no longer can
stop at the abstraction of the video memory...
And to take this one step further. Emulation of this then means you
need to start emulation the video signal generation. And that in turn
means you are going to do emulation of the CRT phosphor.
I have no idea how MAME works, but SIMH does that for vector displays.
Well, MAME also do vector displays. Asteroids being the classical example.
The current implemenation may not be suitable for raster displays, but
it wouldn't be a huge step to add this.
At some level this is obviously rather trivial. We are after all simply
talking about generation of a signal based on the scanning of memory,
and a bit of logic to do the sweeps and sync. An interesting question
becomes at what speed it can be done. Vector displays have a limit on
the number of vectors that can be displayed without flicker, and for the
old machines, that was not too great to start with, so simulations can
certainly deal with it, and can even get away with some cheating to make
it work even when pressed. After all, since you're also faking the
phosphor decay, it can be varied as needed. With a raster display
though, you need to be doing all the lines all the time, at an
acceptable rate, and deal with the additional hardware logic of the CRT.
Again, definitely not impossible. But I'm curious what the speed would
look like, and I cannot remember seeing anyone who have already done it.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: [email protected] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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