how about a solid state alternative to gdrom?

**darkblu** · March 10th, 2006, 02:03

ok, that's just an idea, and as i'm a software guy i may be talking hw gibberish here, but has anybody ever considered replacing the gdrom drive for a flashcard reader emulating the gdrom? i would venture to guess it would require emulating as little as two drive ops: seek and read sector. anyway, has anybody ever bothered to probe the gdrom interface cable?

**semicolo** · March 10th, 2006, 12:34

we've got the pinout but that's all, I've never seen any protocol information.
And I don't have any logic analyser to check it out, but already thought of using something else in place of the gdrom (but without more information it's just a dream for now).

**Masta-G** · March 10th, 2006, 16:01

I think it should be possible but you would probally be near impossible to "emulate" the gdrom so you can boot dreamcast games/homebrew from your flashstick/hd without altering the bios. It would be easier to replace the bios with a generic loader which would support the pinout with a custom made storage system.. would be nice for linux and maybe some homebrew stuff but commercial games wont do I guess...

**darkblu** · March 10th, 2006, 16:38

well, the only problem i can think of with booting from such an emulated "gdrom" would be that it may take some extra op sequence for self-testing and reporting to the host's POST routines. so that would come as an extra work to the basic op seek and op read emulation. but otherwise it would be transparent to the host bios. that is, once the gdrom bus has been analysed, what'd be the problem with providing a PIC on the flash side to emulate whatever protocol, including dummy self-test sequences?

**Tomlo** · March 11th, 2006, 03:37

Even if it were possible why do it, the last time I checked a CD-R is alot cheaper than a flash stick of any size and the only advantage is that it would be able to write to the flash stick but that would require massize modification. It would only be of use to people making games/apps and even then using a CD-RW would be more logical even though the laser is at risk.

Here is some information on the GD-ROM:
http://mozcom.com/~sknkwrks/gdcontroller.html

It explains that basically a GD-ROM is made out of cheap CD-ROM Parts and noting else special, that link should be enough information for anyone who wants to try it.

**darkblu** · March 11th, 2006, 04:46

Originally Posted by Tomlo

Even if it were possible why do it, the last time I checked a CD-R is alot cheaper than a flash stick of any size..

the idea is not to get a cheaper alternative to the iso users. it's meant for coders convenience as such a device would provide for much simper and convenient upload cycle - no burns or transfers over the serial. just a single flashcard which, if big enough, can also hold gdrom images as a bonus.

.. and the only advantage is that it would be able to write to the flash stick but that would require massize modification.

i never originally thought of allowing the dc to write back data to the flash, but now that you mention it, it may not require that much effort, homebrew software aware of the emulation may just bypass the gdrom's original read-only protocol.

It would only be of use to people making games/apps and even then using a CD-RW would be more logical even though the laser is at risk.

i see nothing logical in using cd-rw's for coding purposes on the dc. neither did the early homebrew dc coders - that's why the coder's cable came to be. not to mention that the gdrom is the first part to fail and render a dreamcast unusable, and being as obsolete as it is, the gdrom is dc's achilles heel.

Here is some information on the GD-ROM:
http://mozcom.com/~sknkwrks/gdcontroller.html

It explains that basically a GD-ROM is made out of cheap CD-ROM Parts and noting else special, that link should be enough information for anyone who wants to try it.

with all due respect to the author of that page, it is all speculations and guesswork. and even if it happens to be all correct, i can't see how manufacturing a gdrom at home can solve the issue with lacking gd-r's. a flash-based gdrom emulator, OTH, requires some amount of research, but once designed would be a totally mainstream device that can give the DC the longevity it deserves.

**semicolo** · March 11th, 2006, 14:53

the chip in my dreamcast is a toshiba tc9450af instead of the oti9220

**Tomlo** · March 12th, 2006, 01:17

wow...

Well the chips in different DC's GD-ROM differ in the different models but as far as I can tell they are all made of modified cd-rom parts, I am sure alot of that site is guesswork but the basic idea of that article is to say that the GD-ROM is for most parts a cd-rom which may be easy to emulate.

I also have a Tochiba chip in one of my gd-roms, but didnt check the others, oddly enough I have an old CD-ROM with the OAK and Sony chips.

I figgure that if it were easy to get a dreamcast to write back to its storage medium there would have been people sticking HD's and CD burners sucessfully in them by now expecially since GD-ROM is basically connected by an IDE cable, I dont see how a flash card would be any easier.

It would be faster for coders to use a flash card than burns or transfers over the serial, but it would be massive work.

Instead of an alternative to a GD-ROM wouldnt it be easier to attach the flash drive to the expansion port and instead try to emulate the zip drive. Even though im not sure if it even ever worked its a better candidate since it already has the ability to read and write and all the work could be done externally.

**darkblu** · March 12th, 2006, 02:11

Originally Posted by Tomlo

I figgure that if it were easy to get a dreamcast to write back to its storage medium there would have been people sticking HD's and CD burners sucessfully in them by now expecially since GD-ROM is basically connected by an IDE cable, I dont see how a flash card would be any easier.

apparently to bypass the original read-only protocol you need first to decode it. after that you need to build up a write protocol that (a) would not interfere with the original one and (b) would be understood by whatever sits at the other end of the bus*. so you can't just stick in anything until the original protocol has been analysed. but once that is done, yes, you'd be able to plug in many things at the expense of some interface logic that'd speaks both protocols, e.g. an appropriately programmed pic.

It would be faster for coders to use a flash card than burns or transfers over the serial, but it would be massive work.

no pain no gain. i personally would gladly participate in such a project, just with code only as my electrical engineering is nil.

Instead of an alternative to a GD-ROM wouldnt it be easier to attach the flash drive to the expansion port and instead try to emulate the zip drive. Even though im not sure if it even ever worked its a better candidate since it already has the ability to read and write and all the work could be done externally.

that's not bad either but it has two drawbacks:
1) you won't be able to boot from it.
2) as the gdrom still remains the boot device the moment it dies your dc is a relic, regardless what you have in the expansion port.

* remember the original pc parallel port you'd attach your printer on - by design it was data-write-only (before the bi-directional parallel ports came into being), but people still ran clever bi-directional protocols on it by using a read-protocol together with the write-only protocol, but the party at the other end of the bus had to be smart enough to get that.