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  • Joined: 12 May 2021
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Master System Everdrive on SG-1000
Post Posted: Wed May 12, 2021 4:41 pm
Pretty much self explanatory, but...

I finaly got an SG-1000 and I noticed all the Master System to MarkIII adapters on ebay.

So is it possible to run a master system everdrive on an SG-1000 ?
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Post Posted: Wed May 12, 2021 5:38 pm
You can try, but I doubt if it will work and if it does, maybe not all the roms will be loaded.
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Post Posted: Wed May 12, 2021 6:23 pm
The menu won’t work but I think it is otherwise OK.
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Post Posted: Wed May 12, 2021 7:57 pm
Maxim wrote
The menu won’t work but I think it is otherwise OK.


When I tried it, I was unable to get it to load stored rom. (Using a Chinese clone)
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Post Posted: Thu May 13, 2021 5:14 am
I tried this a while ago and couldn't get any EverDrive to work. I suspect it might need more RAM? I tried both stored (SG-1000) ROM and with a card inserted
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Post Posted: Sat May 15, 2021 12:16 pm
Hi

I did the same a few weeks ago but I was unable.
The adaptor is useful for programming but not for Everdrive. I removed the chip of a 32kB cartridge (transbot game) and replaced it by a EEPROM. I was able to play games

Later, I also expanded the RAM of my SG1000 to 2k and the Sega Basic Level II started. In a few days I am planning to uploads photos

What I have not tested is the everdrive after the RAM expansion, but I am afraid it is not enough.
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Post Posted: Sat May 15, 2021 4:09 pm
I suspect the RAM is the problem.
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Post Posted: Sat May 15, 2021 5:03 pm
Maxim wrote
I suspect the RAM is the problem.


I wonder if it's possible to turn off the console RAM and use cartridge SRAM for this by patching+replacing the EverDrive "menu" program to use Sega mapper registers? However I don't know whether that part of the cartridge "works" at that point of the boot process
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Post Posted: Sat May 15, 2021 6:10 pm
I don’t think Everdrive supports mapping RAM to the right part of the address space. It ought however to be possible to make a version of the OS that works this way. I think it would be interesting to make custom OSes to support this sort of thing as well as other niceties like cover art or different forms of game presentation.
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Post Posted: Sat May 15, 2021 6:24 pm
Good point! I forgot EverDrive might not even implement that part of the Sega mapper protocol

I guess you could put some RAM on your cartridge pin adapter too, along with boot ROM to map it in place of console RAM, and have something like a DahJee adapter but with different addresses. However I don't know whether turning off system RAM even works on these machines
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Post Posted: Sat May 15, 2021 8:34 pm
bsittler wrote
However I don't know whether turning off system RAM even works on these machines
Enri's schematic shows that it only supports the hardware disable - the pin on the card edge he named "DSRAM"
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Post Posted: Sat May 15, 2021 8:39 pm
lidnariq wrote
bsittler wrote
However I don't know whether turning off system RAM even works on these machines
Enri's schematic shows that it only supports the hardware disable - the pin on the card edge he named "DSRAM"


Thanks, I hadn't made that connection! So a hardware adapter may indeed be possible
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Post Posted: Tue May 18, 2021 1:34 am
Just one question: The firmware to list and load the ROMs works as a SMS software, right?

If it is true, using the Master Everdrive on a SG-1000 will need to load a SMS soft to access the menu before loading a SG-1000 ROM, and the SG-1000 is incompatible with SMS softs.

Two ideas to make the Master Everdrive run on a SG-1000 are:

1) Create a dedicated firmware who uses a menu in SG-1000 mode instead of a menu in SMS mode;

...or...

2) Create a firmware who loads the SG-1000 ROM directly without running any menu first. The SG-1000 ROM can be selected by using some text-based file, like a .INI file. Of course, to change the game, the file must be edited to load a different ROM.


This is just theory over an "and if" scenario... I can be saying some "bul****t", but who knows...?
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Post Posted: Tue May 18, 2021 1:50 am
Yeah the menu is SMS software, and I think the logic to auto-boot a game when no SD card is present is also part of that SMS software. Really I think the majority of differences between SMS software and SG-1000 software are around which VDP features they rely on and how much RAM they require, so if the menu can be altered to run in the TMS VDP modes and not assume more RAM than SG-1000 has maybe it could work? The result would also still work fine in an SMS though it would not work in a Game Gear without the addition of palette setup and would not work in Master System 3 Collection or Megadrive at all since those use a VDP lacking TMS VDP modes
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Post Posted: Tue May 18, 2021 3:23 am
It looks like the OS update from Krikzz's web site is just a 32KB (v1) or 64KB (X-series) blob of Z80 code. I'm not saying it'd be easy to rework it into something that only used the older video modes, but there's no obvious FPGA data hiding inside it ... I think it looks doable?
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Post Posted: Tue May 18, 2021 3:49 am
lidnariq wrote
It looks like the OS update from Krikzz's web site is just a 32KB (v1) or 64KB (X-series) blob of Z80 code. I'm not saying it'd be easy to rework it into something that only used the older video modes, but there's no obvious FPGA data hiding inside it ... I think it looks doable?

Maybe this question can be directed to Krikzz.

Who knows if it's possible to make a dedicated SG-1000 menu to make the Master Everdrive compatible with the SG-1000 system, and Krikzz can make such dedicated firmware/menu...

Even more: Maybe a system-detection code can load a dedicated SG-1000 menu if the Master Everdrive is conected into a SG-1000 system, and load the regular menu in any other system... So, you don't need to swap files to make the Master Everdrive run on SG-1000 and SMS systems.
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Post Posted: Tue May 18, 2021 8:15 am
It ought to be possible to make a 32KB menu that supports both video modes. The OS blobs seem to be reverse-engineerable - and there is a source dump for an older version. However much of the complexity is in the file system support for the SD card and the way it interacts with the CPU - I suspect it works by loading large chunks from the SD to RAM and then parsing them. Thus it will need that RAM, and presumably using the cartridge RAM will interfere with its ability to correctly persist saves to the SD card. Maybe there’s more than 8KB of RAM on the Everdrive so the upper area could be used without breaking most games?
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Post Posted: Wed May 19, 2021 5:17 pm
I would love a firmware revision of everdriver running over the SG1000. Meanwhile, I have tested a .sg rom on the everdrive running over the SMS.
After a turning-on without the SD card, it directly starts without loading the OS menu
.
But this empty SD card everdriver running on the SG100 has not started. It blocks at a green screen. I don't know it whether it is a RAM or VDP problem.

My SG1000-II is mooded with 2kRAM instead of default 1kB. I have ordered a 8kB chip to mod it again. I let you know.
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Post Posted: Wed May 19, 2021 7:43 pm
Another factor that is likely adding to this is the missing memory read and write + IO read and write signals on the sg-1000 cart connector. This was the reason why the sg-3000 multi card didnt work on the sg-1000. They made a new revision a few years back that had extra logic in it to work around these missing signals. The master system is also slightly different as you have separate io request + mem request and read + write pins so its not directly compatible without some extra logic.
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Post Posted: Wed May 19, 2021 8:11 pm
I can definitely run the "v1" firmwares in MEKA. It initializes the screen, displays the text "Settings reset to default, press any key" in mode 4, and then doesn't actually find the correct interface to the FPGA and reboots to the same screen every time you press a button.

Looking in MEKA's debugger, the menu is definitely making use of having 8KB of RAM available, such as a VDP upload queue at $D580, and other stuff at $D180 and $DF80.
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Post Posted: Wed May 19, 2021 8:47 pm
wasup wrote
Another factor that is likely adding to this is the missing memory read and write + IO read and write signals on the sg-1000 cart connector. This was the reason why the sg-3000 multi card didnt work on the sg-1000. They made a new revision a few years back that had extra logic in it to work around these missing signals. The master system is also slightly different as you have separate io request + mem request and read + write pins so its not directly compatible without some extra logic.


With that said.. tyere is actually a /memreq, /read and /wrote on the sg-1000 cart comnector so you could use a not gate on the /memreq to make your own /ioreq and that would make it compatible with the master system usage of the pins. Thats all assuming the everdrive actually uses the /ioreq pin... if it doesnt, all of what ive said can be ignored.
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Post Posted: Wed May 19, 2021 9:00 pm
It tentatively looks like the v1 hardware OS doesn't use the I/O ports at all. On a boot in MEKA, it writes (only) to special MMIO registers at $FFF8, $FFF9, and $FFFC.

Disassembling "os-v9.mso" doesn't show any I/O to anything but the VDP and joypad registers. It looks like it expects some kind of interface in the $8000-$BFFF region afterwards.
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