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30th-Aug-2012 02:44 pm
Let there be light:
2012-08-30 GD-EMU proto V2 #1

And there was light:
2012-08-30 GD-EMU proto V2 #2

More pictures to follow soon :)

Status so far:
Voltage regulators - check
MCU starts - check
Bootloader operational using 3V3 UART - check
MCU JTAG - check
C runtime stub + simple exception handling - check
Status LEDs - check
UART 115200 8N1 console - check
Interrupts - check (need to investigate if registers are really properly saved though)
External RAM - check (problem found, should be fixed now)
High speed SD interface - in progress

Random fun fact: Many SD/SDHC cards exhibit various little quirks in SPI mode so the code needs to be aware of those to work properly in every case. One would think the native SD protocol is so tightly standardized that there should be no such surprises. Well, I just found a bunch of 2GB Kingston SDs that respond to ACMD41 with bad CRC7...

EDIT: Turns out the R3 answer is the only one not protected by CRC7, that space is marked as reserved and just filled with all-ones. I'm still not getting the busy bit within reasonable times on these Kingstons but I suppose reading the docs few more times might teach me something new again.

Anyway, here's the actual thing:
2012-08-30 GD-EMU proto V2 #3

Now it's a proper prototype, with all these wires and blinking LEDs. A few things are still missing on the PCB but right now I need to get SD protocol working so I can fetch FPGA configuration image and test it.


High speed SD interface - check
DMA on SD i/f - check
Basic FAT support - check
FPGA - in progress

I'm using my own FAT library, which has no write support but it was designed to be fast while consuming as little RAM as possible. In fact current SD cards are so fast it makes sector buffering impractical, since the lookups and LRU queues kill any gains with additional overhead. I suppose it'd be different if the CPU was clocked above some 400MHz and had some fast L1 cache.
Right now I get average of ~10MB/s in test that seeks to random part of 1.2GB file and reads 1-3500 consecutive 2352-byte long chunks. This is to simulate RAW image reads for GD-ROM. So pretty well I'd say, a nice boost compared to 2.5MB/s I got over SPI.

The native SD interface required a pretty much complete rewrite of some code, so I'm not 100% sure it's stable and all, but seems to work for hours without problems so far.
3rd-Sep-2012 01:15 pm (UTC) - Questions!!!
I have some questions,

1. Price??? (not exact price an estimation)
2. What do you believe will we have something before Christmas?
3. Will futures like:
-Usb hdd support
-Usb game loading
-More advanced game selection
-Other planed features?
exists in your mind?
4. Feature firmware updates for bug fixes or improvements?
3rd-Sep-2012 02:10 pm (UTC) - Re: Questions!!!
Read the next blog entry I'll make soon.
3rd-Sep-2012 01:51 pm (UTC) - This will sell like hot cakes!
Just go Kickstarter with this project and you'll see how successful it will be! Then we make it go viral and bam, you're rich! Man, I am so excited with this, this is a dream come true! You rock dude, you're GOD!!!
3rd-Sep-2012 02:10 pm (UTC) - Re: This will sell like hot cakes!
Read the next blog entry I'll make soon.
18th-Oct-2012 06:50 am (UTC)
I'm looking forward to this going 'gold'. My Dreamcast has trouble reading GD-ROMs but works fine with CD-R.

How about cooking up a broadband adapter as your next project? ;D Technically it *should* be simpler since you wouldn't be dealing with proprietary data formats. The network chip Sega used is common as dirt and IIRC the expansion port is a modified subset of the PCI bus.
20th-Oct-2012 02:00 pm (UTC)
Someone in Japan did try that, with some success. Unfortunately that page no longer exists it seems.

AFAIR it was the Realtek chip plus Altera or Xilinx FPGA to emulate the PCI layer. Quite frankly it was not a very cost-effective solution :)

If it wasn't for compatibility with all current software I'd go for older ISA-based Realtek (10Mbps only is still enough) and just connect it pretty much directly to the modem port. Wouldn't be a problem to write a Linux driver for that, and perhaps modify the homebrew that used BBA (including GD rippers). The games and WWW browsers though... not so easy.
20th-Oct-2012 01:53 pm (UTC)
good work however i do have some questions
...is there a limit on sdhc size?
is the dreamcast bios need to be re-writen to handle the interface?


im kind of worried about yet another image format
20th-Oct-2012 10:37 pm (UTC)
I may be forced to impose a limit in order to keep the code simple. We'll see. So far I've tested it on 8GB SDHC without problems. I don't have any bigger cards at the moment :)
As for the BIOS, it stays as-is. The whole idea was to just swap the drive for a 100% compatible replacement and not have to worry about anything else. It's also why there won't be any fancy GUI - because the BIOS stays unmodified.

There's a way to convert GDI or CDI into new format and it takes just a minute or even less. You only need to do it when you put the image on the card (though I suppose Makaron will support that format as well), so it's not a big deal. I really with people would understand that it's not a PC, there are no gigabytes of RAM for file caching, and even keeping track of multiple open files is slowing things down.
24th-Oct-2012 05:00 am (UTC) - Congratulations :)
Congratulations man, you made something special here, I hope that you sell the boards in a close future in that case I will be like "shut up and take my money" ha ha, your project will revive many dreamcast I'm sure. I understand you with all those trolls making bad comments just ignore them and take all the time you want to complete the project, I had same incident with a similar project some time ago, about reading the maplebus (I made a prototype to connect dreamcast controller to a PC by USB HID) I post some info in a forum and then the trolls want that project NOW but the working prototype is all that I want to do (of course I share all my info and gave some advise those that want to do it) you know what I mean...
24th-Oct-2012 11:01 am (UTC) - Re: Congratulations :)
Connecting Maple to PC (via USB or otherwise) it also something I was looking into. I've seen some AVR-based projects that can work with DC gamepads but only because there is little data being exchanged there. Maple is being handled by tight software loop and it kinda works but just barely.

I wanted to make better interface that could be used along with my emulator and also support VMU and PPP. Problem is, I don't really see how it could be done without some additional logic on the Maple side to handle the state changes on data lines. FPGA would be an overkill, and discrete logic is probably too complicated. So, a small PLD chip would be best, it would include a simple shift-register for that purpose. But I never really made any attempts to test this theory in practice :)
5th-Nov-2012 01:32 pm (UTC)
Well in fact it's something like the xk3y for xbox 360 you're building here right ?

(but i think it's harder beacause the dreamcast don't use sata)

keep up the good work ! !
17th-Nov-2012 11:11 am (UTC) - Nice !
I have done myself the reverse engineering of the Sega DC Atapi bus some years ago (2009) :

Some pictures :

The goal was the same : replace the GD-ROM and keeping the maximum compatibility level.

This is nice to see that someone else make more progress on with this board !


Jeff / HxC2001
20th-Nov-2012 02:01 pm (UTC) - Re: Nice !
I see you've also used DE1 board.
12th-Apr-2013 01:09 am (UTC) - Complete?
Any chance this is complete as of yet?
16th-Apr-2013 06:19 pm (UTC) - Re: Complete?
Sorry but no, it isn't. Can't say more at this time.
10th-Jul-2013 01:59 pm (UTC) - still on it?
first awesome clean almost perfect job !!:D

are you still working on the project ?
17th-Jul-2013 11:25 pm (UTC) - Re: still on it?
In spare time. Which is quite rare commodity these days.
25th-Aug-2013 05:29 pm (UTC) - Region?
First of all, wow this looks so awesome! I'm gonna buy one as soon as it's available!

Second, will this make the Dreamcast region-free?
28th-Jan-2014 01:42 pm (UTC) - Looks awesome!
I would love one of these to play with.

I have a few DC's laying around I use, and some spares.

Really great project and i wish you the best of luck :)
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