Search found 49 matches

by Sauraen
Fri Nov 23, 2018 5:40 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

Anyway, another mystery solved! Yeah! I was wondering why it wasn't just uniformly 24 layers... By the way, any PCM rate that is not an integer multiple of 24 FM ticks will eventually have sound artifacts . I don't know if software developers were aware of this. Probably not. Anyone who has rudimen...
by Sauraen
Thu Nov 22, 2018 5:57 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

My implementation -so far as v0.61 of JT12- was assuming that a 24 CSR (circular shift register) only had an update point, so it would take 24 FM ticks to get new data in. That also made sense in view of the length of the BUSY counter, which Sauraen had reported to count for 32 FM ticks. However, t...
by Sauraen
Wed Nov 21, 2018 5:53 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

So I wonder if the original YM2203 structure of an input multiplexer, fed by the external data input on one side and the output of the shift register, followed by a 12-stage shift register was actually used twice in series. Thus having a total of 24 stages, where feedback goes from stage 24 to stag...
by Sauraen
Thu Nov 09, 2017 6:08 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

My understanding with the DAC "loud" test bit is that normally, channel values are output in an "impulse-like" fashion, for a fraction of their time slot (I think it should be 1/4, since there are 24 clock cycles per complete computation cycle and there are 6 channel values to output during that tim...
by Sauraen
Wed Apr 26, 2017 5:48 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

I do not understand what the interaction with the clock is. If I set to read LSB data and then read for 24 cycles, I am getting the LSB of all the 24 operators... but I am losing the MSB! If then I set to read MSB the operators are already at a different value (different clock) so I cannot get to r...
by Sauraen
Fri Apr 21, 2017 5:26 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

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 Sauraen
Tue Apr 18, 2017 3:04 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

I hope I have not lost you with this long post. A bit, but one thing I can say from an initial read-through: 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 cycl...
by Sauraen
Thu Apr 06, 2017 3:23 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

On a side note, do you happen to have this annotated chip image available somewhere, I couldn't find it back in the thread? I've posted small segments from it on occasion, but no. It's a 1.6 GB GIMP image with 6 layers or so (just different types of signals, not broken out into the actual chip laye...
by Sauraen
Thu Apr 06, 2017 3:14 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

Any chance you have located the "Key Code" calculation unit ? This would be a simple unit with a few OR/AND/NOT gates, taking highest 4 bits of FNUM value as inputs and outputting a 2-bit value (LSB of 5-bit Key Code value, MSB being BLOCK bits). Since this value is used by both EG and PG unit, it'...
by Sauraen
Tue Mar 14, 2017 7:37 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

I was wondering if you ever figured out the LFO and how it works exactly, especially regarding Phase Modulation. I never did a full reverse engineering of it, but here's what I have (from private messages to jotego): The LFO seems to have 3 sections: [*] 7-bit linear prescaler. The test bit 0x21:1 ...
by Sauraen
Mon Feb 27, 2017 9:08 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

HardWareMan is correct, those are large drive transistors, not ESD protection devices. The one between OUT and AVCC is the driver for the output pin, and the two in a pair near the "Control" label are indeed for driving the positive and negative clock lines throughout the chip. These are labeled in ...
by Sauraen
Sun Aug 14, 2016 3:40 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

operators are shifted arithmetically (not logically) by 5 bits The top 9 bits of the 14-bit operator output are sent to the accumulator, which adds the operators within one voice. So there's no question of shifting--it just takes the top 9 bits and discards the bottom 5. Only on PC where you are ac...
by Sauraen
Wed Aug 10, 2016 4:18 pm
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

1) It looks like 9-bit signed, but it's a little hard to tell since you have to read the lower 8 bits and the upper 1 bit separately. But it does appear that if there's nothing playing (or after power-up), the values is 0--it would be 0x100 if it was unsigned like you say, and that's definitely not ...
by Sauraen
Mon Aug 08, 2016 2:05 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

I'd buy one of these if you feel like making 2 instead of 1, Sauraen. Wish I had time to assemble the kit myself, but alas. Hit me up if you feel like making another. I'm flexible on the price. (serious offer btw, I'm fully aware of how much time and effort goes into a project like this) I apprecia...
by Sauraen
Sun Jul 31, 2016 6:12 am
Forum: Sound
Topic: New Documentation: An authoritative reference on the YM2612
Replies: 859
Views: 385624

Re: New Documentation: An authoritative reference on the YM2612

I should have known. The SYNC signal I was looking for isn't bit 15 of the test read data. It's much simpler than that. It's on the TEST pin. *facepalm.jpg* Bit $2C:7 indeed selects whether the TEST pin is an input or an output. But it's the opposite of what I initially thought (since it was "common...