HDD (or flash) instead of a CD, questions...

eteream · Post by **eteream** » Fri Aug 27, 2010 9:19 pm

I am wondering if this is possible:
1) physicaly attaching a HDD into SCD.
2) modifying the BIOS to access HDD instead CD while playing games.

The BIOS is the only code wich access to CD at low level?
or there are games that run CD directly? or do it all of
them?

Any other problem?

TmEE co.(TM) · Post by **TmEE co.(TM)** » Sat Aug 28, 2010 11:42 am

You can do it, since games are supposed to use BIOS for accessing the CD drive. If some game doesn't then that game will not work.

However you got one problem : CDDA. You need an additional microcontroller setup to facilitate it and if you go that route, you might aswell just emulate the CD drive and have no need ot mess with the BIOS itself.

8bitwizard · Post by **8bitwizard** » Mon Aug 30, 2010 3:14 am

Replacing the BIOS to make that work would be a lot of trouble, especially because of the problem with CDDA audio. Also, the Sega CD is not an IDE device. I think the Xbox was the first console to use an IDE interface for optical drive / hard disk.

It would be much less trouble to make a RAM cartridge that can read from an SD card.

Unless of course your point is to run "backups", in which case get a proper backups unit. Or better yet, get a chipped/softmodded Xbox or PSP and run an emulator.

Post by **KanedaFr** » Mon Aug 30, 2010 9:13 am

I'm personnaly interested in this topic for a simple reason : MegaCD lifetime.
The CD drive (lens...) won't live forever and don't know how long we will be able to find replacement part....
So something like a HDLoader would be very interesting...

I started to think about it 2 months ago...but, as you said, I don't see (yet?) how to handle CDDA....perhaps a dedicated MP3 decoder connected to SR/L2 ?

HardWareMan · Post by **HardWareMan** » Mon Aug 30, 2010 12:45 pm

KanedaFr wrote:how to handle CDDA....perhaps a dedicated MP3 decoder connected to SR/L2 ?

Yes. Or you can store whole image uncompressed and output cdda as stream 44.1kHz/16bit/2channels on DAC. I think some controller and CPLD required, but it is possible.

Post by **KanedaFr** » Tue Aug 31, 2010 7:50 am

....unless it would be easier to replace the CD drive (and all logic chips coming with) by a new one....
I know it's hard because the logic chips are on the mainboard and that drive speed could alter FMVs

I don't know what the best approach :
'virtual' CD drive or alternative CD drive ?

HardWareMan · Post by **HardWareMan** » Tue Aug 31, 2010 10:23 am

KanedaFr wrote:I don't know what the best approach :
'virtual' CD drive or alternative CD drive ?

I think, virtual CD drive is more attractive because in case of flash using it will be quiet, less power and enough fast (and for image replace too!). To able play CD-DA, we need DAC, some fast controller (AVR or something, I don't know, must think about it) and big enough CPLD/FPGA. It's all possible, if required doc's are available. Is there any?

Post by **KanedaFr** » Tue Aug 31, 2010 10:51 am

about MegaCD hw ?
sure, follow the link

a quick schema of the hardware is on MegaCD/Hardware/Cdh-iv-horz.gif

lc89510 datasheet is easy to find
KSS240a is harder, the only one I have is a pinout sheet...in russian

more on Eidolon

HardWareMan · Post by **HardWareMan** » Tue Aug 31, 2010 11:19 am

KanedaFr wrote:KSS240a is harder, the only one I have is a pinout sheet...in russian

Can you show it?

Gerrie · Post by **Gerrie** » Tue Aug 31, 2010 11:27 am

There *should* be a datasheet on Eidolons-Inn that covers the CD controller IC (LC89510). It's a datasheet of a hardware compatible controller (the first 16 or so registers are the ones if interrest). I've uploaded it a long time ago and is way better then the other LC89510 sheets floating around the web.

Post by **KanedaFr** » Tue Aug 31, 2010 12:08 pm

HardWareMan wrote:
KanedaFr wrote:KSS240a is harder, the only one I have is a pinout sheet...in russian
Can you show it?

almost the same that the one available at http://www.4shared.com/get/REMknPft/Aju ... -240A.html

Gerrie wrote: There *should* be a datasheet on Eidolons-Inn that covers the CD controller IC (LC89510). It's a datasheet of a hardware compatible controller (the first 16 or so registers are the ones if interrest). I've uploaded it a long time ago and is way better then the other LC89510 sheets floating around the web.

there is a datasheet package uploaded by Pablo
I think you talk about the datasheet about the SAA7380 with a very interesting feature LC89510 compatible with ATAPI interface (make it possible to use a standard CD Drive ?!)

Gerrie · Post by **Gerrie** » Tue Aug 31, 2010 12:20 pm

KanedaFr wrote:I think you talk about the datasheet about the SAA7380 with a very interesting feature LC89510 compatible with ATAPI interface (make it possible to use a standard CD Drive ?!)

I can't access Eidolons from my work, but yes that's the datasheet I (and others) used for SegaCD emulation.

Post by **KanedaFr** » Wed Nov 10, 2010 9:06 am

I recently found an interesting linkabout CD emulation.
It's about emulating a CD from an ISO on a SD Card...

Chilly Willy · Post by **Chilly Willy** » Wed Nov 10, 2010 6:33 pm

KanedaFr wrote:I recently found an interesting linkabout CD emulation.
It's about emulating a CD from an ISO on a SD Card...

Yeah, like that, but with an old fashioned interface, not a USB interface.

Post by **KanedaFr** » Sat Nov 13, 2010 9:25 am

sure....
now I have to find the best way to do it :
- replace the KSS with a logic board
or
- replace the logic (LC89510,...) with another one