JTAG of Cave CV1000 PCBs

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Buffi
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JTAG of Cave CV1000 PCBs

Post by Buffi »

I've been writing up some stuff about how JTAG of CV1000 PCBs work. Maybe it's of interest for some users here. Makes it quite easy to dump U4 if you have any weird revisions.

https://github.com/buffis/cv1k_research/tree/main/JTAG
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parodius
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Re: JTAG of Cave CV1000 PCBs

Post by parodius »

Very interesting. Any chance of being able to access the U23/24 sound data flash chips further down the road ?
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Buffi
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Re: JTAG of Cave CV1000 PCBs

Post by Buffi »

Not through JTAG no
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pegboy
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Re: JTAG of Cave CV1000 PCBs

Post by pegboy »

So correct me if I'm wrong, but won't this allow you to convert one game to another? Other than the sound rom, you should be able to dump/reprogram the PCB code/graphics?

So for instance, with this allow me to convert a DFK 1.5 -> 1.0 or Futari 1.5 -> 1.0 and back again? I'm assuming those both use the same sound ROM so it would work perfectly?
Buffi
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Re: JTAG of Cave CV1000 PCBs

Post by Buffi »

pegboy wrote:So correct me if I'm wrong, but won't this allow you to convert one game to another? Other than the sound rom, you should be able to dump/reprogram the PCB code/graphics?

So for instance, with this allow me to convert a DFK 1.5 -> 1.0 or Futari 1.5 -> 1.0 and back again? I'm assuming those both use the same sound ROM so it would work perfectly?
> So correct me if I'm wrong, but won't this allow you to convert one game to another? Other than the sound rom, you should be able to dump/reprogram the PCB code/graphics?

It's possible.

> So for instance, with this allow me to convert a DFK 1.5 -> 1.0 or Futari 1.5 -> 1.0 and back again? I'm assuming those both use the same sound ROM so it would work perfectly?

Both of these are possible. Note that both of those conversions require writing to U2, which is quite scary for a few reasons:
1. It takes 3 days to write (and another 3 to verify)
2. If your NAND has factory bad blocks (common), writing a romset without bad blocks wont work. For this case, the script will disallow it though.
3. If your NAND has bad blocks not in the bad block table, writing may fail as well
4. I haven't tested it much (see docs)

In theory though yes, you could use this for that.
Unless you are prepared to deal with the consequences of it not working (fixable, but requires desoldering/soldering), I wouldn't attempt it.

edit: Note that I haven't really looked at the structure of 1.0 vs 1.5 of these games. If it's just adding more data to the end of U2 blocks, upgrades could probably be sped up significantly by only handling the relevant pages, and downgrades might not even need changes to U2. As mentioned, haven't looked at this though!
edit2: Disregard edit above. Had a quick look at it, and suspect you want to do a full rewrite.
Last edited by Buffi on Fri Apr 16, 2021 11:52 am, edited 1 time in total.
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Sumez
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Re: JTAG of Cave CV1000 PCBs

Post by Sumez »

Nice job, Buffi. It's great to finally have this sort of documentation out in the open.
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