Search found 21 matches

by jotego
Mon Nov 26, 2018 12:03 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

All calculations performed in OPN2_PhaseCalcIncrement function actually take 4 cycles on real hardware. I've simplified it as all data used in this function enter to the PG block at the same time. Replicating all latches would be big headache for linear C emulator. Probably there are some other opt...
by jotego
Sun Nov 25, 2018 5:29 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

One FM clock in my code is 6 master clocks. For example in Genesis Plus GX emulator OPN2_Clock is called 1.27(7.67/6) million times per second(for comparison MAME code works at 53.267 KHz). Like real hardware my implementation updates registers within 12 FM ticks. Look carefully to OPN2_DoRegWrite ...
by jotego
Sat Nov 24, 2018 6:27 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

I have no any other documentation unfortnately. YM3438 die shot is pretty clean, so just labeling certain bits was enough to understand it's logic. Vectorizing entire chip is overkill i think. About cycle accuracy: Emulation core runs at YM2612's internal FM rate(i.e 24x of YM2612's sampling rate)....
by jotego
Sat Nov 24, 2018 6:02 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

nukeykt wrote:
Sat Nov 24, 2018 4:47 pm
Sik wrote:
Sat Nov 24, 2018 4:33 pm
But register $2A only has 8 bits...
LSB bit of PCM is mapped to $2C:3.
Exactly, and MSB is inverted in order to get correct sign for addition with other channels:

Code: Select all

pcm_data = { ~pcm[8], pcm[7:0] } ;
(Verilog code)
by jotego
Sat Nov 24, 2018 8:15 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

Probably my cycle accurate YM3438 emulator (which is basically translation of YM3438 schematic to C code) can give some insight about YM2612/YM3438 internals. That's an impressive piece of work. I will look at it carefully. Particularly I want to learn more about the undocumented bits. I do not see...
by jotego
Fri Nov 23, 2018 10:49 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

Surprise surprise, I was wrong. I thought I remembered them being 24 units/layers deep, and they are, but they're broken up to two groups of 12, with logic in between and at the beginning and the end. I don't have time right now to fully transcribe it, but given the other findings here, it seems re...
by jotego
Thu Nov 22, 2018 12:35 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

The operator parameters (for all units: EG, PG, OP) are stored in 24-deep circular shift registers whose outputs are basically just the control signals for all the units in the chip. There's no way to write to the middle of these--they can only be written to when that particular operator's data com...
by jotego
Wed Nov 21, 2018 9:21 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

I am quite confident from viewing the die shots, and it seems to be sufficiently confirmed from testing, that whenever you write a data value, BUSY gets set, and gets cleared exactly 32 cycles later. On the die shot it's just a 5-stage counter, not connected to anything else. Of course the chip act...
by jotego
Thu Apr 27, 2017 9:34 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

Very informative. I have updated the wiki on the JT12 repository with the information. I am setting up a board to take direct measurements so expect news in the coming weeks about the latest topics we have discussed.
by jotego
Wed Apr 26, 2017 8:08 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

The chip could have a different logic to generate the BUSY for the keyon I looked again, and as far as I can tell this is not the case. The BUSY timer's only inputs are chip reset and a signal indicating a data address was written, and it has one output. This output goes to a unit which puts values...
by jotego
Fri Apr 21, 2017 2:22 pm
Forum: Sound
Topic: too many YM2612 infos ?
Replies: 14
Views: 3327

Re: too many YM2612 infos ?

I disagree with closing YM2612 topic. It should stay as discussion thread. Also I disagree with making LFO, EG, PG threads. Threads should made when someone have question about it, and he make topic with this particular question. As any other thread. Sound implies not too many themes at all: YM2612...
by jotego
Fri Apr 21, 2017 8:58 am
Forum: Sound
Topic: too many YM2612 infos ?
Replies: 14
Views: 3327

Re: too many YM2612 infos ?

We need somebody to scourge through it and make proper reference documentation from the data there. The problem isn't even the length, it's that it's a disorganized mess where unless you know the exact page ahead of time you'll be screwed if you're looking up for something in particular (not to men...
by jotego
Fri Apr 21, 2017 8:52 am
Forum: Announcement
Topic: Future of SpritesMind
Replies: 38
Views: 9713

Re: Future of SpritesMind

I am a newbie in the forum but let me share my two pennies about this topic: -I think this is a valuable forum about Megadrive hardware and software development. -I think that is already enough. It is always hard for people to come and together and make projects in their spare time. The most we can ...
by jotego
Tue Apr 18, 2017 12:04 pm
Forum: Sound
Topic: too many YM2612 infos ?
Replies: 14
Views: 3327

Re: too many YM2612 infos ?

At the moment that topic is the source of information for YM2612 of the whole internet. We have to be careful about messing with it as there are links pointing to it all over the internet...
by jotego
Tue Apr 18, 2017 9:49 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 378759

Re: New Documentation: An authoritative reference on the YM2612

Very interesting. Let me comment: The thing is that, if your implementation is correct, it would take a maximum of 18+23=41 cycles to update the keyon states of all four operators. Which means, you could write a certain keyon value, wait the 32 cycles the dumb BUSY timer (and the datasheet) told you...