ChanServ changed the topic of ##yamahasynths to: Channel dedicated to questions and discussion of Yamaha FM Synthesizer internals and corresponding REing. Discussion of synthesis methods similar to the Yamaha line of chips, Sound Blasters + clones, PCM chips like RF5C68, and CD theory of operation are also on-topic. Channel logs: https://freenode.irclog.whitequark.org/~h~yamahasynths
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<andlabs>
oh someone dumped that ROM fo rsure now?
<andlabs>
I remember people being unsure about the contents for some reason
<cr1901_modern>
YM2413 ROM isn't dumped AFAIK, and doesn't have debug modes to dump it. But VRC7 does
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<Foone>
sounds like we need to get some of them to john mcmaster for decapping so the ROM can be optically read out
<Lord_Nightmare>
the ROM is implant rom, its a pain in the ass to stain. I think JM has already tried once a number of years ago
<Lord_Nightmare>
he may need anothe ym2413 or several to try again
<Sarayan>
The default instruments?
<cr1901_modern>
Correct. Staining doesn't have a 100% success rate :(
<cr1901_modern>
Sarayan: Default instruments? AFAIK, there's only one programmable instrument on ym2413, and Idk if it has a valid value on reset (probably not)
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<cr1901_modern>
But of course if you point that out, you'll (not totally unjustified) be pointed out as a pedantic ass using esoteric knowledge to one-up someone who cashed in on the "lucrative" retro market.
<Foone>
eh. inaccurate is a problem, but "cashing in" and "surface level" doesn't bother me that much, to be honest.
<Foone>
the dremels-and-open-carry stuff is more bothersome
<Foone>
but yeah... my own personal interaction with him definitely supports the inaccurate and surface-level take
<Foone>
I basically sent him a bunch of disks with a spreadsheet saying what they were
<Foone>
then I wrote out some more spreadsheets to clarify the stuff he didn't undrestand, then we voice-chatted to clarify it even more, then he did a video which was full of "and there's this disk and I have no idea what it is!"
<Foone>
so much so that I had to do a big thread explaining what a lot of stuff was because he did such a shit job of showing it off
<cr1901_modern>
.oO(Of course, doing a deep dive into obscure media would also be a lot of work for a video)
<Foone>
regarding how hard to stain the YM2413 is, I wonder if anyone has used that method where you slowly laser-cutter your way down to the die, which in theory should give you a still-functioning exposed die
<Foone>
and then attached probes directly to the die to read out the ROM that way
<cr1901_modern>
This was how the Sound Blaster DSP was read out, according to ej5
<cr1901_modern>
As well as the DSP-1 in the SNES (both the crashing plane and not-crashing plane version :P)
<Foone>
the DSP-1 in the Pilot Wings cart, you mean, then.
<Foone>
because that's why there's two versions: it's in the cart, not the console
<Foone>
but yeah, makes sense
<cr1901_modern>
yes
<cr1901_modern>
Same DSP used in Super Mario Kart and a few others. I just remember how the plane crash was an incredibly obscure and amusing piece of knowledge when I first learned about it
<ej5>
we didn't use the laser method though
<ej5>
i've tried the laser method before and it burns everything to a crisp
<Foone>
I think you may have turned it up too high
<ej5>
basically with the sb dsp we decapped with fuming nitric
<ej5>
then i did a partial reverse engineering of the entire 8051
<ej5>
i was looking for test modes. they do exist, but they were too complicated for me to figure out in a reasonable amount of time
<Foone>
I imagine all large lasers have a knob on the side that goes from "amuse cats" to "correct eyesight" to "burn chips" to "explode the moon"
<cr1901_modern>
>and then attached probes directly to the die
<cr1901_modern>
Well, the SB DSP was read out doing this, correct?
<ej5>
so instead i figured out how the ROM worked, then read it out 1/8 bit at a time using a probe station
<ej5>
just one probe
<cr1901_modern>
ahhh
<ej5>
with a probe station it's really only practical to get 1, maybe 2 probes at once
<cr1901_modern>
How do you read out addrs that aren't used in the ROM?
<cr1901_modern>
if you can only insert 1 probe?
<cr1901_modern>
i.e. the Creative banner I imagine is unused data, but I saw it in the hex dump of the first 16-32 bytes you posted in a paste.
<cr1901_modern>
(forget how much data was in the paste- not much)
<Sarayan>
that's the implant rom in the middle, right?
<ej5>
i connected the 8051 in external address mode and fed the data bus with the NOP instruction
<Foone>
ej5: speaking of pulling data out of a rom... would you happen to know if that 80186/80188 logic analyzer probe you got on saturday would work with an NEC V40?
<ej5>
so the program counter just counts up from 0, hits all the addresses.
<ej5>
not offhand
<cr1901_modern>
ej5: oooh, that makes sense. I thought maybe the DSP had a special pinout or something that doesn't expose external addr mode
<ej5>
(naturally, when i try to google "NEC V40" fucking chrome expands it to "NEC V404" and tries to sell me an LCD monitor)
<Foone>
heh, same
<cr1901_modern>
or that when external addr mode was enabled, the internal ROM doesn't output to the bus
<cr1901_modern>
to the internal data bus*
<ej5>
yeah the address bus is always connected to the ROM, but the data bus on the ROM has an enable line
<ej5>
so in EA mode that enable line is always false
<ej5>
i just picked off the digital signal right before the enable gate
<cr1901_modern>
^that was my follow up
<cr1901_modern>
Sarayan: That would be my guess, comparing to VRC7 (implant ROM middle left)
<ej5>
apparently the V40 is not pin compatible, so i don't think it would work
<Foone>
ahh, ok. thanks for checking
<ej5>
why, do you have a V40 system?
<Foone>
several! Specifically, the Videonics video editing system
<Foone>
it's got a weird undocumented ROM chip in it and being able to debug the CPU would be a good first step towards dumping the ROM
<Foone>
realistically I probably will get the ROM contents by continuing to trace out the PCB and then making some educated guesses about where address pins might be, but it sure would be nice to skip all that work
<Foone>
the system is crazy fun. it's that one that stores the OS on a VHS tape
<ej5>
wild
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