Sega Dreamcast System RAM 16MB+ & JTAG hack

hy bro , you can do it?? O_O or what happend

 

I know this is an old post but if you're still looking for linux, here's a build:
http://dcemulation.org/files/homebrew/dclinux-010605.7z

it's probably not the most recent one, but that's it.

 

Never saw this thread the first time around.

@LeGIt did you ever make any further progress?

Sounds like an awesome mod.

 

Bumping. Anything new with this?

 

hi bro, any news o progress or already is closed the project

 

I know it should work in theory, but before I had time and no money, now I have money and no time. Hopefully I'll be able to get back around to it as and when but I doubt it will be any time soon sorry. It should be quite simple for someone to pick up where I left off though

 

Interesting. I actually tried to do a RAM doubling hack in 2009.

I took 2 DCs, desoldered the RAM from one of them to use on the second. Stacking two chip on top of each other just barely works if you bend all the legs from the donor straight down. I left one address line string out into the air and planned to attach it to CS2, no drilling should be needed for that, just a bit of wire. See some photos I took at the time:





I even have finished code somewhere in preparation of finishing this hack, but unfortunately it ended with me blowing the thing up. Result:



I can't quite figure out what happened here. If I could I would try again. I'm pretty sure I didn't short anything because I went over and checked all contacts 3 times before turning the power on.

 

You cant just stack the ram, you need to use the extra address (or chip select line) line to enable/disable the chips to switch between them.

Did you leave an address line leg up or the chip select leg?

 

Quite, but even missing that it shouldn't blow up.

The chip select leg was left up.

 

which were the ram chips of more capacity found (reference)?
and were they pin compatible or almost pin compatible?

Regards

JOSÉ

 

I haven't tried it, but the Micron MT48LC4M32B2P (any speed grade) looks like a good bet.

Pinout is almost identical - the only difference is pin 21, which is NC on the original chip and A11 on the Micron part.
Mode register bits are the same (the Micron also supports CL1, which the Samsung part doesn't)
Both devices have 4 banks, 256 column addresses and use 64ms 4096 cycle refresh

In theory, all you should need to do is connect the A11 input pin to CPU_A21 and it should work...

 

mmmm.. i have to try that,i am not shure but ,my dc under dreamshell running under sd card has a strange bug ,some times when restart the dc ,it refuses to detect the sd card,must put unconected for at lest 30 minutes,then i power on and detects card again ,i am almost shure the ram capacitors remain charged and the ram don´t clear .....
well a little of topic but any help would be good

Regards

JOSÉ

 

With new emu GDrom or USB GDrom; could we use virtual memory like internal HDD for Xbox, to improve Ram avalable?

 

I m interested in this project too... I m an electronic/informatics technician, with good soldering skill and with a laboratory with good equipment. I m going to mod my Dreamcast with dual bios, internal VGA and SD card. This could be my next testing mod. I can help you giving you some memory modules from old rams and graphic cards if you need and if I find some on old hardware devices I have. I can even give you desoldered modules of ram since my soldering rework station is ESD safe and perfect to do those things

 

Now a little bit off topic question. Tonight I read about internal VGA and SD card and I had an idea... Maybe it s stupid, and maybe someone just tried this way. Leaving all the differences in ram quantity and in the process of games boot between Naomi/triforce and Dreamcast would it be possible to use an SD card adapter as dimm board to emulate Naomi games on Dreamcast? I know you have to write an emulation software and mod parts of games to use less ram but maybe... I read that SD card adapter is 5mb/s fast and could be a decent bandwitch. Sorry if my question is stupid but I have this idea spinning around in my head all the night

 

The sd card goes through the serial port which I think is around 250 KB/s in terms of speed.

 

you can see a speedtest in this site:
http://multimedia.cx/eggs/dreamcast-sd-adapter-and-dreamshell/
545kbytes/sec in write and 672 in read,and maybe it could perform better if you try with a uhsIII or a class 10 sd card if supported because this test was performed with a pny 2gb card wich I suppose is an older one.I can t test it now,because I m waiting for components to mod my dreamcast,but maybe there are some other problems in my idea...Or else it s strange no one found this solution before.
Once in sdcard the content that should be in naomi s dimm board are I think is optimized to be read from a physical memory so the bandwitch could be ok.Another thing that brought to me this idea is the fact that naomi takes from 3 to 5 mins to push gd files to dimm board so taking virtua tennis 2 in consideration that is about 75 megs on naomi you can see the writing speed of dimm board is not fast.
But don t know...only asking about this crazy idea,maybe someone could tell me I m thinking wrong

 

VA1 MB:
Bottom Side Between SH4 and PVR is R147.
Connect a wire on the side closest to SH4 is CPU PIN 15 - A19: Pulled U/D on R147
Bottom Side Between SH4 and PVR is R122
Connect a wire on the side closest to SH4 is CPU PIN 14 - A21: Pulled U/D on R122

Swap Stock 86TSOP Ram Chips With MT48LC4M32B2P x2
Send the two additional Address lines to PIN 21 on each SDRAM.
=32MB ?

 

So if you guys did end up figuring this out, would it give the free RAM to any game/application on the Dreamcast? I saw someone say they had the code to activate it written. Would this code have to be used as a boot-disc of sorts? Or could it only be used if a game/program was coded to support the expanded RAM?

Cool stuff though. I hope eventually it is figured out and well documented

 

Any apps would have to be written to utilize the added ram. Same issue with the Xbox apps and later PSP's that had more ram. When you do the 128mb ram mod on Xbox it only works for the newer updated apps that utilize it basically. This would be good for homebrew stuff going forward that took advantage of it. Older games and stuff wouldn't know the difference.