Forsaken Well

All Rheas have been shipped so it’s time for that small GDEMU run. I will open orders, as usual, on Saturday. As promised I will try to better match the time to USA west coast. If my calculations are correct you should be able get up at 8 and still have time for shower and breakfast. I’m not making it USA exclusive but I do reserve the right to reject other orders.

Also, people, the “Name” field in the ordering form? It’s for your name. Preferably it should match the Paypal one, it makes my life easier. I’m not selling your personal info on the side to Facebook or Google (or anyone else for that matter), I’m not that evil. Besides Paypal probably already did that long ago 🙂

Now, I wanted to explain a few things regarding FM Towns Marty because it gets a lot of flak from uninformed people. Some even actually own the console and still repeat that BS anyway…

First thing is the Marty CPU. The 386 “haha, slow piece of shit” SX. Well, I now have a working generation 3 Towns tower and have run some actual tests to compare. Here are the RAM read and write results, done for 8, 16 and 32-bits access patterns:

Marty FMTg3
Read (ms) Write (ms) Read (ms) Write (ms)
BYTE 17170 12315 21600 12155
WORD 8590 6170 10810 6080
DWORD 5565 3140 5410 3050

Noticed something? Write is faster than read – that’s curious but not that uncommon, depends on any extra cycles that have to be added to meet setup and hold times to make things reliable. Plus the tests aren’t identical. But the real shocker is how Marty is actually way faster at 8- and 16-bit reads, and pretty much matches 32-bit ones even with it’s reduced 16-bit bus. How is that possible if the tower has a 386DX CPU running at the same clock speed?

The answer is actually simple – wait states. Now this is a bit of my speculation but back in ’88 or so, when Towns was close to release, DRAM was still slow and expensive. And much like today the faster you went, the more it cost. So first generation Towns had a slow RAM that required 3 wait states to work, and my guess is that setting was left for gen 2 and gen 3 to keep things at the same speed and not break any compatibility. The CPU was the same anyway.

Marty was released after gen 3, along with generation 4 and the new U-models that had the monitor integrated in the case. These too were 386SX based. By that time though DRAM was considerably faster and so it’s running with zero wait states, basically removing that SX half-width data bus penalty. “Wait,” you might say, “wouldn’t optimized software deal mostly with 32-bits anyway?” – and that is faster on the DX, if not by much. Plus what about VRAM? Well, I’ve run some more tests:

Marty FMTg3
BYTE 15090 23625
WORD 7560 11815
DWORD 7550 5920
FONT 367450 383870

These are VRAM writes, and the last test is font rendering (again measured in ms). As you can see Marty is way faster except for 32-bits – which is now exactly the same speed as 16-bits due to CPU having to split each access into two and no clever optimizations for that taking place. So only very optimized 32-bit block copy routines will be faster on the 386DX. But hey, that’s probably what games mostly use, right? Perhaps, but 386 doesn’t have any cache memory (not counting TLB) and you still need to actually run the program, and x86 code is messy. Which means every instruction is RAM read, often more than one if the fetch is not power-of-two bytes long, or longer than 4 bytes, or unaligned. At which point Marty will pull ahead and indeed the font test was faster on the SX-based system.

So, TL;DR is Marty has it’s issues but slow CPU is not one of them.

By the way, there is a program that can change the wait states on gen 1-3 Towns, though keep in mind the actual slow RAM is still there, you can’t reduce it by much and expect the system to still work. As a rule of thumb you can go one less wait state with each generation, so my unit can actually go to zero and still seems to be stable. I’ve tested that setting too and, except 32-bits, RAM reads are still slower than Marty. But with writes getting a bit faster and 32-bits too, the font test is now clearly won by the tower. Starting with generation 4 there is also a FAST mode, basically zero wait state mode guaranteed stable by manufacturer. Though to be frank if the 386 isn’t cutting it for a game you want to play, neither FAST mode nor a 486SX will help. You need a DX2 or Pentium based machine.


UPDATE: GDEMU orders were open what, 3 minutes, and everything went. In fact it’s possible some of you will have to wait a bit more since I might have oversold a bit – this was a small batch after all.

423 thoughts on “Forsaken Well

  1. It’s like two trolls practicing for the big leagues. This is their proving ground.

  2. I’m probably like super duper lucky, it’s my first time buying and i manage to get in on both the Rhea the last time and Gdemu this time. The Open order time is not even in favor of my region, I just did some guessing on the “clues” that was mentioned in gdemu’s post. I don’t sit whole day in front of the computer, i just carry on with what i do/sleep then alarm and come back to it when i think it will open up. Actually i think of it as a game, guessing the release time. ^^ good luck to the rest who have yet to get one. Use Control+F5 for refresh.

    • I also got very lucky, my first time buying was a GDEMU a few months ago and the pre-order was up for like 10-15 minutes. I’m located in The Netherlands and it was 12:00 PM when the pre-order was opened. I’m now waiting for my next pre-order which is the Phoebe 🙂

  3. So no phoebe this weekend either?…lolz…..dieing to stop having to buy CD-Rs….if the discs arent real and in the original case, i dont want them around! Out of mostly every retro disc based console only need discs for Saturn, Sega CD, PCEngine CD, Marty, and PCFX – i love to shrink that list as often as possible -SD4Me, spoiled by my gdemu and all my everdrives and other ODEs!

  4. Is there a way to check what Rhea firmware is currently running on a Saturn?
    I updated to the latest Rhea v3.90 firmware and im using RMENU v0.2,0.

    • Hi gdemu,

      I have an boot up issue for my GDEMU. please view below video. I’m not able to boot into menu, but able to load gdi file(not cdi) by clicking the switch button on gdemu. I also tried input a cdi file into folder 02, not able to load by clicking switch button. I formatted my sd card as fat32 cluster size 32kb. Do you have any idea? Thank you,

      • Are you sure the image is good and the region matches your console? Does it work as burned CD in your Dreamcast?

      • please see below current setting of GDEMU.ini file, my DC is Japan version(VA1) . It works fine on regular GDrom, no issue with loading original DC game disc.

        The “GDmenu_v0.6.cdi” image file was included in “GDmenu_v0.6(24-08-2016).zip” I downloaded from “link” page.

        Seems “auto_region = 0” is not on GDEMU operation page, it’s for Rhea and Phoebe root setting, I give it a try to input to GDEMU.ini file, but seems not work.

        open_time = 500
        detect_time = 250
        image_tests = 1
        auto_region = 0
        reset_goto = 1

      • GDEMU doesn’t do region patching and anyway the menu software is all-region and should alway work. Try renaming the file to disc.cdi. What video cable are you using, VGA?

      • I removed auto_region from GDEMU.ini file, and renamed the file to disc.cdi. but still get the same issue. would it be my console issue? i try a few games. it can load the gdi file in 02 folder by clicking the switch button, but no able to load cdi file under the same folder. do u have “GDmenu_v0.6.gdi” file? i wondering if it work or not, cus i can use GDEMU to play gdi game file. Thank you,

      • Can you boot any CDI images at all? Try downloading some DC demos or homebrew games.
        Also, you can always try re-flashing the device with the current firmware from my page. In case you somehow got a wrong version or something.

      • I’m unsure but it looks like you renamed the menu to disc.cdi. (With a full stop at the end)
        Try disc.cdi
        Also check to see if your operating system has hide extensions for known filetypes enabled – if it is then disable it to make sure the filename is correct 🙂

      • To gdemu,

        yes, i try a few dreamcast games in cdi image . non of them work. It’s only works when i input gdi image in 02 folder. That’s why I wanna know if you have GDmenu_v0.6 in gdi image format so I can give it another try~~

        I updated the firmware to 5.15.0 when i first receive the device. so it should be in most current version.

        To Nightbreed,

        my windows OS always untick “hide extensions for known file types”, no full stop at the end of cdi, Thanks for your comment

      • I’ll re-check my code on weekend but there is a good chance you have a somewhat rare late VA1 with newer BIOS. SEGA disabled CD-ROM booting in a (too late) attempt to curtail piracy.
        Does your console still have a working drive? Are you able to boot any burned CDs?

        The menu software could be re-packaged as GDI but I don’t have a version like this ready. Give me a few days, I’ll see if I can dig up some DC tools to try that.

      • Just a Thought, but I am going to guess this buyer is in Japan? Shouldn’t Dreamcast Systems be Plentyful and super cheap? Why not just try another Dreamcast VA1 and see if that solves the problem. WOuld be a good way to trouble shoot if it is system, ODE or software.

      • To gdemu,

        Thank you, will give another try with burned cd. I appreciate your help.

        To Abe,

        I’m a US buyer…; I have another Dreamcast, but with VA0 motherboard. I do think about to get another Dreamcast for test…; but it’s not easy to find a VA1 Dreamcast in Boston area…

      • To gdemu,

        I have tried to boot a few burned CDs, non of those burned CD work. I know you are busy with gdemu; phoebe’s shipment and others. But I guess I may need your help to re-package menu software to GDI format so I can give another try. Please let me know if you get any update; Thanks again for your helping.

      • Wow!!!!
        I can not express my gratitude to you in words; It works!!! Thanks so much for your helping; my Dreamcast can now boot into the menu and load other gdi files from the list…; Thanks a again; appreciate your helping.

        This console was purchased from Tokyo by my friend and shipped over to US. Is it easy to dump the bios? If you interest it; I will try search the method or tutorial online and see if I’m able to dump the bios and send to you

      • You won’t be able to dump the BIOS since all the tools are packaged as bootable CDs. Plus you’d need a BBA or serial dongle. I can maybe rewrite my own code and try to store the result on GDEMU… but that’s a very low priority for me right now.

  5. for the moment still not get the paypal invoice for me.
    Maybe because i’m in the bottom in the preorder list (added by gdemu).

  6. Thanks GDEMU. Got mine today here in NC, USA. The west coast time zone ordering really helped out. Hopefully you can do the same thing for the rhea/phoebe at some point.

  7. I just got my GDEMU. I’m on the west coast of the US. Thanks for doing this @GDEMU!

  8. I just got my GDEMU as well. I live in the Boston area. Thanks!!!!

  9. Just got my gdemu in the mail today. Let me tell you about the shipping, that was fast as hell. Coming from overseas to NJ, USA. I was expecting a lil over a month until it reaches me. Thank you very much GDEMU, i look forward to the weekend to test out this bad boy. Much love.

  10. Any update on when the Phoebe sale will happen? Also, do you have a timeframe for when you will open up DocBrown sales to everyone?

    Finally, have you had a chance to make any progress on PCE CD? Is it going to work with the Duo/R/RX or just in the Addon Super CD module? I have been trying to find out the answer to that last one for a while.

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