Theorizing how to replace a VIC-II by hardware.

Well... I'm starting this as a discussion about what would be needed to
replace the VIC-II with hardware that would emulate it and expand/enhance
it.

For a start, I'm a reader. I read, ideas comes to my mind and then I ask, so
I can learn from people that actually know.

So...

AFAIK (and I'm telling this for people to know what is what I do know,
accepting corrections of course) , the VIC-II do cares about

- Display text and graphics.
- DRAM refresh.
- System clock generation.

--For the first, it reads from the CHAR ROM for text, or from RAM when
instructed to do so, mostly by KERNAL but also by custom routines. For
graphics, it reads from RAM, and is the task of the CPU how and what to put
in RAM for the VIC-II to render it as graphics (actually the text does also
works this way).

- For the second, the VIC do read data from the RAM chips just for them to
force their contents not to be lost.

- For the third, the VIC do send a clock pulse from one of its pins to one
of the pins of the CPU, that then outputs this signal to the rest of the
system.

So its inputs are power, of course, the clocks generated from the 8701 or
equivalent circuit, and the address and data bus.

And its outputs are the video signals, the DRAM refresh lines, the IRQ
lines, the BA line to control the CPU and stop it when needed.

Then, there is the read/write pin and the chip select pin as control pins.

So: what would be needed to emulate first of all for a C64 to believe that
the VIC-II is still there?

For me:

- The clock output. The CPU, and the rest of the system, won't work without
it.
- The DRAM refresh lines. DRAM contents won't last without it.
- The raster line register. There are things the CPU does when the raster
line is in certain locations, like triggering IRQs.
- The missing thing I am not aware of and that you are telling me.

With an FPGA or a PIC fast enough, maybe there would be a way to implement
this **as a first measure** to make a C64 *think* there is at a logical
level a VIC-II there, because at an analog level, the system doesn't care
about if there is a video signal coming from it or not, or if the graphics
are actually rendered: the CPU just read or write registers, gets controlled
by the BA line or IRQ, and gets ticked in by the clock pin.

The next step would be reading from the proper places (ROM, RAM or COLOR
RAM), and render the bitmap image taking care of the effects supposedly to
be applied by the raster line tinkering that the demos do (of course sprites
also have to be rendered).

And finally, get that bitmap converted to an output signal that would be in
a format that could be converted to *real* HDMI (digital) or component /
svideo (analog) video. It could be even encoded inside network packets to
have a VIC that could be remotely viewed through a network connection. This
final stage could get rid, maybe, of the PAL/NTSC (and SECAM) limitations,
because digitally it could be upscaled and up-frame-rated to modern
standards, applying filtering - or just having a 4K version of the classic
VIC graphics with the pixels upscaled to the size of actual bricks.

NOW is your turn (that I would actually appreciate as I love to learn)

- What do you think?
- Is it doable?
- Does it worth the work to do it?

Thanks all.

-- 

Saludos y cerveza.




--
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