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

For hardware talk only (please avoid ROM dumper stuff)
eteream
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Post by eteream » Sat Apr 30, 2011 1:03 pm

I read a bit of the implementation of the LC89510 and since it has his own memory, memory map and code, to replace it, we need a CPLD+RAM+ROM+PIC or, more simply, a FPGA.

And, well, in a FPGA we can implement the whole MCD. So, as someone said, there is no point here.

I dont understand why some say that changing ROM code is a hard way. If the CDDA problem doest exist it will be the easiest (as far as I see...).

And well, this is not about making backups. To make a backup simply put a CDR in your drive and press burn.

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Nemesis
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Post by Nemesis » Tue May 03, 2011 1:02 am

Unfortunately my webhost is down right now, so I can't host this properly, but this might be of interest to some of you:
https://rapidshare.com/files/460329424/LC8951.zip

It's a 127-page scan of the complete, official documentation from Sega on the Sanyo LC8950 family of controllers used as the CD controller in the MegaCD. I found it on the web while mining for documentation awhile back. I don't think it's very widely known about, but it's a lot better than the other documentation I've seen referenced in this thread. Might be of interest for some of you working on the MegaCD.

Chilly Willy
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Post by Chilly Willy » Tue May 03, 2011 2:44 am

eteream wrote:I read a bit of the implementation of the LC89510 and since it has his own memory, memory map and code, to replace it, we need a CPLD+RAM+ROM+PIC or, more simply, a FPGA.
It looks easier to replace the CD drive and emulate the interface the LC8951 uses via a CPLD.

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HardWareMan
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Post by HardWareMan » Tue May 03, 2011 3:46 am

Nemesis wrote:Unfortunately my webhost is down right now, so I can't host this properly, but this might be of interest to some of you:
https://rapidshare.com/files/460329424/LC8951.zip
Very interesting... Thanks.

Eke
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Post by Eke » Tue May 03, 2011 11:51 am

Nemesis wrote:Unfortunately my webhost is down right now, so I can't host this properly, but this might be of interest to some of you:
https://rapidshare.com/files/460329424/LC8951.zip

It's a 127-page scan of the complete, official documentation from Sega on the Sanyo LC8950 family of controllers used as the CD controller in the MegaCD. I found it on the web while mining for documentation awhile back. I don't think it's very widely known about, but it's a lot better than the other documentation I've seen referenced in this thread. Might be of interest for some of you working on the MegaCD.

yep, it covers all CDC registers/interrupts with lot of details, more accurate than the SAA7380 manual which is on Eidolon's Inn. It was also uploaded there as JPEG files, same place as usual (thanks to ElBarto !):
http://www.megadrive.org/~elbarto/md/Do ... al/LC8951/

I don't know where this comes from but Synergisticis actually the company who developed Silpheed :wink:

eteream
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Post by eteream » Tue May 03, 2011 9:31 pm

Chilly Willy wrote:
eteream wrote:I read a bit of the implementation of the LC89510 and since it has his own memory, memory map and code, to replace it, we need a CPLD+RAM+ROM+PIC or, more simply, a FPGA.
It looks easier to replace the CD drive and emulate the interface the LC8951 uses via a CPLD.
As I see it:
The CPLD to do the memory map (MCD runs about at 12mhz) to controller memory and controller registers, also you need a little of memory to do so, and a pic to read from SD which accept commands through mentioned registers.

I've noticed that the rom modified approach also needs a CPLD to decode bus directions. The CDDA problem can be solved using a multicore pic, one core to read data, another to read music and send it directly to the music DAC, for example.

In any case FPGA now are enough cheap, can provide exact simulation, have space for several systems, VHDL or verilog are not so much difficult coming from C, so...

panzeroceania
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Post by panzeroceania » Sun Jul 17, 2011 8:25 pm

This would be a great project. It would preserve the hardware, and allow you to play with theoretically less loadtimes. I'm looking to get floppy emulation hardware for a lot of my old PCs (X68000, FM Towns, etc) so an optical disk emulator also seems like a good idea.

There are already people doing such for the Wii and Xbox 360 I think. It'd be a more noble cause for older game systems though where piracy isn't the first motive. it'd also be a great convenience factor like flashcarts as apposed to always having to have your entire library available in your playing room.

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KanedaFr
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Post by KanedaFr » Mon Jul 18, 2011 6:29 pm

Unfortunatly, I never found details on how they did CDLoader on PS2, WII, XBox....
It would be interesting....

panzeroceania
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Post by panzeroceania » Wed Jul 27, 2011 11:59 pm

I'm sure if you asked on their forums you could get a little more information behind the hardware

http://www.wodejukebox.org/

http://www.xodejukebox.org/

LocalH
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Post by LocalH » Fri Jul 29, 2011 12:39 am

I know that the game loaders for the PS2 use a little bit of resident code to hook into the system disc I/O routines to feed the data from another source (whether USB, HDD, Ethernet, or IEEE1394 depending on the loader). Might be doable on the MCD through a BIOS replacement (don't most games read data through the BIOS routines?).

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KanedaFr
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Post by KanedaFr » Sat Jul 30, 2011 10:49 am

I first thought update the bios was the thing to do but experts here told me not ;)

Chilly Willy
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Post by Chilly Willy » Sat Jul 30, 2011 8:22 pm

Replacing the CD at various levels moves from needing more software (changing the BIOS) to more hardware (emulating the CDROM or one or more of the CD interface chips). So there are pros and cons for whatever method you take.

Least hardware/most software: simple CPU driven IDE port attached to 68000 with all new BIOS fully rewritten to access IDE devices.

Most hardware/least software: replace CD drive mechanism with hardware interface that emulates said mechanism.

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HardWareMan
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Post by HardWareMan » Sun Jul 31, 2011 1:47 am

If all software uses BIOS for access to CD-ROM then no need so low level hardware emulation, right? But, we don't know for sure, is there some games, which do some direct access to CD hardware, so low level emulation is the best and hardest way. And you don't need to change the BIOS or any other software.

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KanedaFr
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Post by KanedaFr » Sun Jul 31, 2011 7:07 am

interesting note, HWman.....
perhaps emu autors could help us on this one : did you meet games which rely on fully emulated hw and not only bios ?

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TmEE co.(TM)
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Post by TmEE co.(TM) » Sun Jul 31, 2011 7:32 pm

There are 2 kinds of CDC used so the games that use HW directly have to have 2 pieces of code for each thing.
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