RE: [stella] Joystick Port Baud rate...

Subject: RE: [stella] Joystick Port Baud rate...
From: Manuel Polik <cybergoth@xxxxxxxx>
Date: Thu, 15 Nov 2001 02:19:29 +0100
Hi Glenn!

>>Does this make any sense to you hardware guys? :-)

>Since the 2600 has no interrupts, and no input buffer, 
it's hard to do truly 
>reliable general purpose I/O.

But what I want to do is 'special purpose I' only :-)

>I think you'd be better off building a MIDI interface 
on the cartridge 
>itself and maybe having a chip on the cart 
automatically write to a RAM area 
>(it can be read-only to the VCS, but read-write to the 
chip on the 
>cartridge).  That way the RAM area can act as a FIFO 
buffer and you can 
>process the MIDI data that accumulates during VBLANK.
>You'd have to have a hot address the 2600 can hit to 
indicate that it's 
>processing the buffer (so that any new data gets put in 
a secondary area if 
>necessary) and another hot address that tells the chip 
to clear the ram and 
>copy the secondary buffer data back to the main buffer.

I see your idea... Hm... I'm not sure if I should like 
it or not. It's too much cheating somehow :-)

Next step would be placing the TIA inside the cartridge 
too, and throwing the VCS away :-)

One thing, that is part of my current concept, is that 
no video output is necessary at all, not even a TV is 
needed. So I don't need to care about VBLANK or any of 
that stuff. I can use _all_ cycles for 

>Along the line, the chip in the cartridge could 
possibly do some 
>pre-processing of the MIDI data so that it is presented 
to the 2600 in an 
>easy-to-digest fashion.  For instance, you could pre-
quantize the 7-bit MIDI 
>volume data to the 4-bit 2600 volume setting.  You 
could also interpret 
>channel/voice data and convert that into direct 
distortion settings in the 

All that preprocessing, if really necessary could be 
done by the circuit plugged into the joystick port, too. 
And this circuit is needed anyway, for the opto-

>If you wanted to simplify things further, rather than 
an expensive to design 
>chip, you could have some kind of MIDI interface 
software for the PC that 
>performs the preprocessing in real-time before sending 
the signal down the 

Well, I have a PC, my brother still uses an Atari ST and 
our friend with the studio equipment is running a MAC of 

>According to my rough calculations, at MIDI speed, 
assuming that you are 
>totally maxing out the MIDI bandwith just for the 2600, 
you'd have 64 bytes 
>per 60th of a second to process.  I don't see how that 
would ever happen in 
>the real world, though, when controlling a device that 
only has 2 sound 

Hm... everything sounds sooo doable. So why isn't any 
MIDI stuff existing for the VCS so far? :-)

>The networking layer on the PCs could be peer-2-peer 
and handle all the 
>connection issues for the 2600.

Hehe... and I recently thought that creating a 2-Player 
Roguelike game with 2 VCS connected via Joystick ports 
is way over the top :-)


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