I think most of us would agree with everything you said.
The problem is that the easiest way to upgrade the tone generator would be to remove the existing MSM5232 and simply replace it outright with the new one.
I am reasonably sure that we can duplicate the exact behavior of the MSM5232 by the replacement 40 pin module EXCEPT that the envelope generator behavior will be 100% digital as opposed to the existing half digital, half analog control.
The way it works now is the 80C85 does all of the 8 bit envelope generator math but then outputs the EG level into an 8 bit digital to analog converter because the MSM5232 has VCA inputs for each voice level.
In the digital replacement, we're going to have the 80C85 send the EG level to the drop in replacement TG via digital write messages. And the new TG will then do its own 32 bit digital math to produce the appropriate voice output levels.
I don't think there's a big distinction to be made with the above. They're essentially the same. But I look forward to hearing other opinions.
The new TG will have to emulate the existing 16', 8', 4', 2' feet outputs for the 8 DCO's. When it switches to enhanced mode those outputs will EACH be a voice. The existing MSM5232 does mixing of the digitial voice outputs internally and then there are two blocks of resistor ladders that determine square and triangle waveforms. In the new device, we will duplicate that behavior but in advanced mode the outputs will be analog waveforms for each voice.
And an interesting side feature will be that the analog inputs that were used for each DCO envelope generator level might be able to be retooled to provide modulation control of the oscillators.
It really opens up many new possibilities because by using a 32 bit processor for tone generation we can probably offload a ton of things away from the 80C85 and let the new TG do it. This will dramatically alter the capabilities of the synth.
As I've said before already, I am going to need help! Volunteers please.
/Mike
On Monday, October 13, 2014 10:55 AM, "John David Duncan john.david.duncan@... [korgpolyex]" <korgpolyex@yahoogroups.com> wrote:
Hi,
I've missed a little of the discussion but I think I've seen three different ideas:
- replace the 8085 CPU
- replace the tone generator
- add a tone generator based on a new processor chip
Of these three ideas, I like adding a tone generator best.
It maintains the value of all the software and hardware work Mike's done so far.
It can be done in a way so that one 8085 code base works both for people who have the new tone generator and people who don't.
It preserves the Poly 800. By this, I don't mean every facet of the Poly 800 is worth preserving. I'm glad to see tape support go out the window. But I would prefer to keep the ability to play the original patches (via some upgrade path) and make the original sounds, rather than simply transform a low-end 1980s synth into a low-end 2010s synth.
JD