Emulating Sega Pico

Nemesis · Post by **Nemesis** » Wed Jun 04, 2008 4:33 pm

Alrighty, the Pico unit arrived in the mail this afternoon. It's taken all evening, but I've got a "working" adapter, and I've dumped a few roms. I say "working" because it's not really working yet. I've got a bad joint or a stray bit of solder somewhere or something, because I'm getting a little bit of intermittent data corruption, so I'm going to consider my current dumps to be bad until I can get the adapter reliable. I'll have another look tomorrow when I've got a fresher pair of eyes.

Oh, and while I remember, there are a couple of errors in the Pico cart pinout on that japanese site. Pins 22 and 25 are swapped, and they need a little more explanation as to how they relate to the Mega Drive interface IMO:
22 OE(IC11#8*) - Connect to AS (B18) on Mega Drive
25 CE(CAS0) - Connect to CE0 (B17) on Mega Drive

Nemesis · Post by **Nemesis** » Thu Jun 05, 2008 12:25 pm

Ok, here are the first two Pico cartridge dumps to be released in the public domain:

http://nemesis.hacking-cult.org/Pico/Mi ... 28U%29.zip
http://nemesis.hacking-cult.org/Pico/So ... 28U%29.zip

I'll be dumping a larger batch of Pico cartridges soon.

TascoDLX · Post by **TascoDLX** » Fri Jun 06, 2008 10:19 am

Nicely done, Nemesis! I only took a peek but rest assured I'll take a closer look when I have the time.

Both games handle level 3 ints but not level 5 ints (the latter will crash Mickey's game).

notaz · Post by **notaz** » Mon Jun 16, 2008 5:35 pm

Hey Nemesis, can you do some sound recordings of Sonic PCM samples from the real hardware? I just wonder how they are supposed to sound.

Nemesis · Post by **Nemesis** » Mon Jun 16, 2008 10:34 pm

Yeah, I can manage that. My second Pico unit arrived last week (the first one was "sacrificed" to make the dumper). I haven't tried it out yet though. I'll power it up and capture some audio sometime this week.

BTW, once my new etching tank arrives, I should be able to rig up a reverse adapter: Running a Mega Drive cartridge on the Pico. I haven't had a serious look at it yet, but potentially, I should be able to load some custom code into a flashcart and run it on the system. If there are some specific tests you want to run on the hardware, I might be able to arrange it in the near future.

tails92 · Post by **tails92** » Tue Jun 17, 2008 9:23 am

According to the docs, the Pico doesn't manage the addresses of the joystick like a normal megadrive would.
For the matter, I tried booting some megadrive roms with a changed header in the Pico-enabled picodrive emulator, and they wouldn't get any input.
I don't know if this also applies to the real hardware, but if it does, you'd either need to patch the megadrive games or to come up with some way to put the joystick status the same way as it is done on a stock md.

Nemesis · Post by **Nemesis** » Tue Jun 17, 2008 9:36 am

I wasn't planning on running regular Mega Drive games on the Pico, although that could be an interesting experiment. What I meant was I could compile some basic test roms for the Pico, eg, to test the behaviour of the PCM chip, and run them on the system using a Mega Drive flashcart.

Chilly Willy · Post by **Chilly Willy** » Tue Jun 17, 2008 4:37 pm

If there weren't too many places to patch, seems you could use a Game Genie to make a Genesis cart work. You'd need patches for each one, though.

Nemesis · Post by **Nemesis** » Tue Jun 17, 2008 10:14 pm

I'd just modify a ROM and run it off the flashcart if I wanted to get a Mega Drive game running on the Pico. There are too many differences to just use PAR codes to patch. The control interface doesn't even work in approximately the same way, it's likely attempts to write to the 0xAXXXXX memory block would lock up the system, there's no Z80 at all, and it's probable the game would need to write "SEGA" to the protection address on the Pico in order to do much at all. Besides, the Game Genie or PAR wouldn't run on the Pico for the same reasons a game wouldn't run on the Pico. It wouldn't be difficult to modify a Mega Drive game to at least boot from the Pico, but I'm not planning on trying it at this point in time. Too much other stuff to get done.

Chilly Willy · Post by **Chilly Willy** » Wed Jun 18, 2008 12:51 am

That different, huh? I haven't looked at the doc yet - I was thinking it was more like the Atari 7800 where it was just an Atari XL with the hardware at a different location.

ElBarto · Post by **ElBarto** » Tue Jul 08, 2008 6:17 am

Thank you very much for those information, I've started to add it in MESS. (of course you're credited).

cdoty · Post by **cdoty** » Fri Jul 11, 2008 6:32 am

ElBarto wrote:Thank you very much for those information, I've started to add it in MESS. (of course you're credited).

Out of curiosity, how will MESS handle the display of the pages?

ElBarto · Post by **ElBarto** » Sat Jul 12, 2008 8:43 am

cdoty wrote:
ElBarto wrote:Thank you very much for those information, I've started to add it in MESS. (of course you're credited).
Out of curiosity, how will MESS handle the display of the pages?

For now I don't know how I will do that, maybe use the artwork part of MESS but the artwork cannot be "clicked".

Charles MacDonald · Post by **Charles MacDonald** » Fri Jul 18, 2008 10:59 pm

The ADPCM chip is a NEC uPD7759 that has been rebranded by Sega. Here's the datasheet for the same 52-pin QFP version of the chip the Pico uses:

http://www.modelektronik.com/download/upd7759.pdf

It's emulated in MAME, so it should be a snap to support. If you need timings, the blue thing to the left of the chip is a ceramic resonator which probably runs at 640 KHz.

notaz · Post by **notaz** » Sat Jul 19, 2008 11:29 am

Thanks for the info. Looks like you are right, and the chip sits there in the slave mode.

Great to see you here, Charles!

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Emulating Sega Pico

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