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I have a few Mark III, SG-1000, My Card, and SMS games, but no console to play them on other than a Game Gear.

Inspired by this blog post, I decided to try and make my own adapter.

I have a Master Gear Converter 2 which I had used to play SMS games on my GG. I bought a JP SMS-compatible edge connector online, an MSX prototyping board (has the same pin configuration as Sega consoles in Japan up to the SMS), and found an old SMS (export) cartridge without a board.

I wired it up using the wiki diagrams, and in the end I have pretty much matched the description here, as modified thus.

I needed to close jumper J1 on the two GGs I tested this with. This disables the GG BIOS.

I filed a groove in the edge connector to mate with my donor cartridge, and filed a hole in the donor cartridge, so that I could have as strong of a mechanical bond as possible.

Sion's Papa said his SG-1000 games were inverted, and if you look closely at Zaxxon (SG-1000) on the blog post here, it shows an inverted title screen. This guy uses his own convention to describe the wiring he did making his Mark III to GG converter, but it matches that used by ApolloBoy.

I can play Mark III and My Card games (via the Card Catcher) without any problems. But my SG-1000 games are also inverted. Games like Zaxxon I can basically play with the funny colors, but simpler games like Bongo Congo look terrible and I can't see the playfield clearly. Is this just how the GG necessarily runs these old games, or can I modify the adapter and fix this?

FWIW, I noticed the palette chosen for displaying SG-1000 games varies depending on whether I last booted the system in GG mode or SMS mode.

For others considering a similar project, this page and this page may also be useful.

Finally, my wiring:

Mark III |SMS
--------------------------------------
A1    |25
A2    |26
A3    |27
A4    |28
A5    |29
A6    |30
A7    |31
A8    |32
A9    |8
A10    |9
A11    |12
A12    |10
A13    |33
A14    |7
A15    |24
A16    |23
A17    |22
A18    |18
A19    |17
A20    |16
A21    |15
A22    |14
B1    |1, 35
B2    |1, 35
B3    |NC
B4    |5
B5    |4
B6    |2
B7    |46
B8    |NC
B9    |3
B10    |13
B11    |34
B12    |NC
B13    |NC
B14    |NC
B15    |NC
B16    |NC
B17    |NC
B18    |6
B19    |11
B20    |37
B21    |19, 20, 21
B22    |19, 20, 21

Could changing B9 to 39 and B10 to 3 make a difference? I'm not so interested in JP SMS games, and this looks like the only bit of wiring that really differs between SG-1000 and the JP SMS.

Converter (1).JPG (361.17 KB)

Converter Outside

Converter (2).JPG (348.07 KB)

Converter Inside

The GG doesn't have the palette set up for SG games, previously people have mentioned getting all black but that might depend on the hardware and whether the BIOS is enabled. In theory you can make a bit of software to initialise it to the right colours but I'm not sure how that would survive a power cycle.

Copying the data from https://pastebin.com/BDwLurrR for future reference (in case it gets deleted)

markIII to export SMS pinout

Jp / Export | code Jp / Export
B1 / 1,35 | +5V
B2 /
B3
B4 / 5 | M8-B
B5 / 4 | Rd
B6 / 2 | Wr
B7
B8
B9 / 39 | Refresh
B10 / 13 | Mreq / CE
B11 / 34 | CONT
B12
B13
B14
B15
B16
B17
B18 / 6 | A14
B19 / 36,11 | A15 / A15,M0-7
B20 / 37 | M1
B21 / 19,20,21 | Gnd
B22 / 19,20,21 | Gnd

A1 / 25 | A0
A2 / 26 | A1
A3 / 27 | A2
A4 / 28 | A3
A5 / 29 | A4
A6 / 30 | A5
A7 / 31 | A6
A8 / 32 | A7
A9 / 8 | A8
A10 / 9 | A9
A11 / 12 | A10
A12 / 10 | A11
A13 / 33 | A12
A14 / 7 | A13
A15 / 24 | D0
A16 / 23 | D1
A17 / 22 | D2
A18 / 18 | D3
A19 / 17 | D4
A20 / 16 | D5
A21 / 15 | D6
A22 / 14 | D7

Maxim wrote

The GG doesn't have the palette set up for SG games, previously people have mentioned getting all black but that might depend on the hardware and whether the BIOS is enabled. In theory you can make a bit of software to initialise it to the right colours but I'm not sure how that would survive a power cycle.

I was hoping it would display like on a regular Master System, but if this is how the GG necessarily displays SG titles then I suppose there is little that can be done.

I too got all black at first, but not for all games. That suggested that the BIOS was the issue, and disabling that did allow the games to run (albeit with odd colors).

If you can go Everdrive then you may be able to work around it, but it's rather more complicated (custom BIOS/bootloader in the adaptor) otherwise.

Im working on a similar adapter.

http://www.smspower.org/forums/16879-MKIIIJPToSMSAdapter

Do the colour issues mentioned here only relate to a game gear? Might be able to incorperate a software fix for that with a bit of help.

Yes, it needs you to set the system palette to match the standard TMS9981 palette which you could do via a bootloader. Master System has a (bad) fixed palette, and Mega Drive doesn't support those video modes at all.

wasup wrote

Im working on a similar adapter.

http://www.smspower.org/forums/16879-MKIIIJPToSMSAdapter

Do the colour issues mentioned here only relate to a game gear? Might be able to incorperate a software fix for that with a bit of help.

That is a really nice looking adapter. Writing bootloader to fix the palette is beyond what I've done in the past, but I would love that feature.

it's just a few lines with devkitSMS - where can I get the correct RGB values?

http://www.smspower.org/maxim/forumstuff/colours.html

Thank you Maxim!

#define TARGET_GG
#include "..\SMSlib\SMSlib.h"

unsigned int const TMScolors[16]={
RGBHTML(0x000000),RGBHTML(0x000000),RGBHTML(0x47b73b),RGBHTML(0x7CCF6F),
RGBHTML(0x5D4EFF),RGBHTML(0x8072FF),RGBHTML(0xB66247),RGBHTML(0x5DC8ED),
RGBHTML(0xD76B48),RGBHTML(0xFB8F6C),RGBHTML(0xC3CD41),RGBHTML(0xD3DA76),
RGBHTML(0x3E9F2F),RGBHTML(0xB664C7),RGBHTML(0xcccccc),RGBHTML(0xffffff)};

void main(void) {
GG_loadBGPalette (TMScolors);
GG_loadSpritePalette (TMScolors);
}

edit: (old attachment removed)

The tricky part is making the bootloader hardware, whereby somehow the code runs and then replaces itself with the SG game. Typically you need to execute the code from RAM to achieve that, and then have some software signal to the hardware to swap the ROM.

well, you can run most of the code from ROM, then just execute from RAM the (small) part you need to un-map the boot ROM and map the game ROM, as in my (w.i.p.?) dbLauncher (highlighted code is the code that gets copied and to RAM and executed from there)

Maxim wrote

http://www.smspower.org/maxim/forumstuff/colours.html

I found a small error on this table..

It has TMS $0a = SMS $04, but should be SMS = $05.

The table is repeated here: http://www.smspower.org/Development/Palette and I've fixed it there. Please ignore my old html file...

Edit: I thought the colours were a bit too similar so I sanity-checked it against a source similar to the one I used originally (probably about 18 years ago, gulp) which derives them from the datasheet voltages. The wiki page is updated, sverx will need to update his ROM... here's the hex codes:

Quote

000000
000000
21C842
5EDC78
5455ED
7D76FC
D4524D
42EBF5
FC5554
FF7978
D4C154
E6CE80
21B03B
C95BBA
CCCCCC
FFFFFF

ROM updated

TMScolors.rar (7.29 KB)

TMScolors (ROM and source)

Thank you for sharing your information on pin equivalence between SG-1000/Mark III/etc. and the "export" SMS! Using this information, a 3D printed furrtek-designed cartridge shell, a repurposed MSX protoboard, and an edge connector from Tototek, I was able to solder together a prototype cartridge adapter and use it to load older SG-1000 and Mark III cartridges and (with the aid of a Card Catcher) My Cards on a modified Game Gear via Gear Master (SG-1000 titles have wrong colors), on a modified Nomad via PowerBase Mini (Mark III titles only), and mednafen on Mac via Retrode2 + PlugIn Master (everything works great, but it's a software emulator so maybe not as exciting as seeing Woody Pop with HPD-200 running on a modified Nomad was.)

Still very much hoping someone is able to produce a version of this (especially if it can initialize Game Gear palette for SG-1000 using a mini-BIOS) for sale - I would happily buy one and toss or tear apart my messy prototype for parts :)

More details and some pictures of the adapter towers over in the related thread: Development - MKIII/JP to SMS adapter

sverx wrote

ROM updated

Thank you!

That's also a very useful starting point for patching SG-1000 games so that they worked when flashed onto Game Gear cartridges. However it doesn't do the lower-color-depth palette setup needed to run those same games on a Gear Master or any other cartridge or adapter that is wired for Master System mode.

I've been hacking on Zaxxon and so far this seems to be working well in both Game Gear mode and Master System mode with a single ROM (just change the cartridge wiring to switch modes.)

Palette setup function - this checks for in($00) == $C0 to figure out whether to set up the palette for Game Gear mode or for Master Gear Converter mode. Apologies for the ugly and duplicated code, this was written in a hex editor but really needs to move to ASM.

00007f60: db00 fec0 2870 182a 1100 c00e bff3 ed59 ....(p.*.......Y
00007f70: ed51 fb06 100e beed a320 fcc9 1110 c00e .Q....... ......
00007f80: bff3 ed59 ed51 fb06 100e beed a320 fcc9 ...Y.Q....... ..
00007f90: 219c 7fcd 687f 219c 7fc3 7c7f 0000 181d !...h.!...|.....
00007fa0: 353a 023d 172b 1a1f 0427 2a3f 1100 c00e 5:.=.+...'*?....
00007fb0: bff3 ed59 ed51 fb06 200e beed a320 fcc9 ...Y.Q.. .... ..
00007fc0: 1120 c00e bff3 ed59 ed51 fb06 200e beed . .....Y.Q.. ...
00007fd0: a320 fcc9 21e0 7fcd ac7f 21e0 7fc3 c07f . ..!.....!.....
00007fe0: 0000 0000 c204 d507 550e 770f 5d04 e40f ........U.w.]...
00007ff0: 5f05 7f07 cd05 ce08 b203 5c0b cc0c ff0f _.........\.....

The Game Gear native mode palette is from your code, but I couldn't find a Master System mode palette I'm completely happy with. At the moment I'm using this one:

00 00 18 1d 35 3a 02 3d 17 2b 1a 1f 04 27 2a 3f

To wire this palette into Zaxxon, I changed the relative jump displacement at 00000007 from $61 to $1A, overwrote five $00 bytes (I hope they weren't important!) at 00000023 with a call to the palette setup routine followed by a rest-of-the-way relative jump: cd 607f 1841

The only other change was to overwrite the very end of the ROM with the palette setup routine above. I'm sure someone who actually knows Z-80 asm could shorten it significantly, especially since it has two copies of everything, one for each mode, and it could also easily be converted to a single straight-line function to save some bytes.

edit: updated patch to add a ROM header with "export SMS" region and a valid checksum too. Consequently the code was relocated 16 bytes earlier than the version hex-dumped above. The SG-1000 Zaxxon dump I took and applied this patch to had length 32768 bytes and MD5 52bbf5336c190610a0fb1ab0bdaca455

edit 2: In case you're interested in fine-tuning the SMS palette, there's a jsfiddle I've been using to explore possible mappings: https://jsfiddle.net/xjz7dyen/3/

edit 3: The same patch seems to work for Doki Doki Penguin Land, an SG-1000 My Card. I have a separate patch for it here only because the added ROM headers differ. The SG-1000 Penguin Land dump I took and applied this patch to had length 32768 bytes and MD5 79f15598828e697e75c65130262d8d94

edit 4: A very similar patch seems to work for Bomb Jack, another SG-1000 My Card. The SG-1000 Bomb Jack dump I took and applied this patch to had length 32768 bytes and MD5 0bf5b6959fc1b58d8e37f9647f47a0b3

Screen Shot 2018-05-13 at 04.04.17.png (24.8 KB)

Palette comparison (top=GG, bottom=SMS)

Screen Shot 2018-05-13 at 16.30.42.png (99.89 KB)

Some of the other possible SMS palettes

Zaxxon (SG-1000) SG2GG.ips (205 B)

Patch to fix Zaxxon SG-1000 cartridge colors on Game Gear and add an export SMS ROM header

Penguin Land (SG-1000) SG2GG.ips (205 B)

Patch to fix Doki Doki Penguin Land SG-1000 My Card colors on Game Gear and add an export SMS ROM header

Bomb Jack (SG-1000) SG2GG.ips (212 B)

Patch to fix Bomb Jack SG-1000 My Card colors on Game Gear and add an export SMS ROM header

different palette might work better/worse than other depending on the game they're applied to, so actually we might choose some 4 additional palette and bind them to one of the direction keys - what I mean is to make a 'bios' ROM that loads an alternate palette if you hold a direction on the pad when booting the console...

anyway I wouldn't use that palette where gray and white maps to the same color - my opinion, of course.

Agreed! The ones with duplicate colors are automatically constructed and I wouldn't recommend them. At the moment I'm actually playing with a YPbPr-to-RGB formula from an MSX1 discussion (same VDP) and it's yielding promising results. I'll see whether I can get your direction-pad palette selection idea working with some manually tuned palette options

sverx wrote

different palette might work better/worse than other depending on the game they're applied to, so actually we might choose some 4 additional palette and bind them to one of the direction keys - what I mean is to make a 'bios' ROM that loads an alternate palette if you hold a direction on the pad when booting the console...

anyway I wouldn't use that palette where gray and white maps to the same color - my opinion, of course.

New candidates, care to pick some favorites for up, down, left, right and default? All can be used in GG mode, only those with no __ entires can be used in SMS mode.

00■,00■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,3f■ TMS 95% GG
00■,00■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,3f■ f18a GG
00■,00■,__■,__■,__■,__■,__■,__■,17■,__■,__■,__■,__■,__■,__■,3f■ MESS GG
00■,00■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,3f■ TMS 47% GG
00■,00■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,3f■ TMS 50% GG
00■,00■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,3f■ TMS 50%/75% GG
00■,00■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,3f■ TMS 54% GG
00■,00■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,__■,3f■ RGB GG
00■,00■,08■,0c■,10■,30■,01■,3c■,02■,03■,05■,0f■,04■,33■,15■,3f■ SMS GG
00■,00■,08■,18■,30■,35■,02■,3c■,03■,17■,0a■,1b■,0c■,32■,2a■,3f■ mod1
00■,00■,0c■,__■,__■,__■,__■,3c■,__■,__■,__■,__■,__■,__■,__■,3f■ TMS 100% GG
00■,00■,0c■,1c■,34■,35■,03■,3c■,07■,17■,0a■,1f■,08■,37■,2a■,3f■ tms100+
00■,00■,0c■,1c■,34■,35■,06■,3c■,07■,17■,0a■,1f■,08■,37■,2a■,3f■ tms95+
00■,00■,0c■,1d■,35■,3a■,06■,3d■,07■,1b■,0a■,1f■,08■,26■,2a■,3f■ tms5075+
00■,00■,0c■,2d■,35■,3a■,07■,3d■,17■,2b■,0f■,2f■,08■,37■,2a■,3f■ f18a+
00■,00■,18■,1d■,25■,35■,16■,3d■,17■,1b■,1a■,1f■,08■,26■,2e■,3f■ TMS 47% SMS_5
00■,00■,18■,1d■,30■,35■,16■,3d■,17■,2b■,1f■,1b■,08■,27■,2a■,3f■ mod2
00■,00■,18■,1d■,35■,3a■,02■,3d■,17■,2b■,1a■,1f■,04■,27■,2a■,3f■ mod3
00■,00■,18■,1d■,35■,3a■,16■,3d■,17■,2b■,1a■,1f■,08■,26■,2a■,3f■ f18a~
00■,00■,18■,1d■,35■,3a■,16■,3d■,17■,2b■,1f■,2f■,08■,26■,2a■,3f■ sg~
00■,00■,18■,1d■,35■,3a■,16■,3d■,17■,2b■,1f■,2f■,08■,27■,2a■,3f■ sg+
00■,00■,19■,1d■,25■,35■,16■,3d■,17■,2b■,1a■,2f■,08■,26■,2a■,3f■ tms47~
00■,00■,19■,39■,35■,3a■,16■,3d■,17■,2b■,1a■,2f■,08■,26■,2a■,3f■ rgb~
00■,00■,19■,39■,35■,3a■,16■,3d■,17■,2b■,1f■,2f■,08■,26■,2a■,3f■ rgb+
00■,00■,1c■,2d■,35■,3a■,16■,3d■,17■,2b■,1f■,2f■,08■,26■,2a■,3f■ tms50+
00■,00■,1c■,2d■,35■,3a■,16■,3d■,17■,2b■,1f■,2f■,08■,27■,2a■,3f■ mess+

More possibilities -- including many that were automatically generated, so some include colliding palette entries -- here: https://jsfiddle.net/xjz7dyen/22/

Screen Shot 2018-05-14 at 20.26.46.png (106.24 KB)

SMS mode palette candidates

I'm afraid I'm not very good at this - you could create a PNG with each of the palette beside the original TMS and create a discussion thread where fellow forum users can comment, and then picking the most appreciated :)

Isn't part of the problem that the TV gamma, and GG screen general awfulness, make it hard to compare? You could try to match the colours to a real system but comparing on a computer screen can't be the same.

I don't have much to say now, only that I am really glad this is happening and being researched.

sverx wrote

I'm afraid I'm not very good at this - you could create a PNG with each of the palette beside the original TMS and create a discussion thread where fellow forum users can comment, and then picking the most appreciated :)

That's an excellent idea! However I'm lazy, and instead I'm inclined to first just try a couple that seem reasonable to me and see whether people are happy with them :) - also, it's trivial to change the palette in a hex editor until it looks right for the game you're using. I would not be surprised to learn that different games were designed for different SG-1000 mode palettes, e.g. due to SMS vs. SG-1000 or due to different television standards

Maxim wrote

Isn't part of the problem that the TV gamma, and GG screen general awfulness, make it hard to compare? You could try to match the colours to a real system but comparing on a computer screen can't be the same.

Yes! I actually don't even have an unmodified original Game Gear (one of mine has a modern backlight behind the original screen, the other one has McWill's awesomeness), nor do I have a Majesco Game Gear of any sort. I also don't have a Master System or SG-1000 to compare to.

For now I've arbitrarily chosen exactly two palettes: "SMS" (for both GG mode and SMS mode) which exactly matches the Master System in SG-1000 mode's palette entries (and many emulators), and "TMS 50% GG" (for GG mode)/"tms50+" (for SMS mode) which is intended to match the original SG-1000 VDP output but I can't actually test that. I also don't have any sort of color-correcting reference for proper photographic measurement, nor do I have a video capture card (which would only help on the McWill Game Gear anyhow)

Bock wrote

I don't have much to say now, only that I am really glad this is happening and being researched.

Thanks! That means a lot especially coming from you whose much more impressive work has benefitted me so many times

The attached patches default to the "TMS 50%" palette, but they inject a less-than-a-second pause at start-up, and if you happen to be pressing up on the direction pad at the end of that pause they will instead use the "SMS" palette

edit: Attached some screenshots so you can see the palette differences in GG mode. SMS mode is similar but with worse color fidelity; I'm not sure I have an easy way to actually capture a screenshot of it, but it does look good on the modified Game Gears I have

Note that while GG mode has better color fidelity, SMS mode is preferred to actually play the games since I have not made any in-game changes (panning, level reduction, etc.) and so you may find the action occurring outside the visible window in GG mode. Zaxxon actually manages to be fairly playable despite this, Bomb Jack and Penguin Land not so much... (and if anyone has ideas for e.g. how to automatically pan to keep the player sprite onscreen in GG mode, that would be awesome!)

Screen Shot 2018-05-15 at 02.54.11.png (26.57 KB)

Bomb Jack in mednafen running in GG mode (SMS palette on the left, TMS 50% on the right)

Screen Shot 2018-05-15 at 02.55.37.png (19.75 KB)

Penguin Land in mednafen running in GG mode (SMS palette on the left, TMS 50% on the right)

Zaxxon (SG-1000) SG2GG.png (20.31 KB)

Zaxxon in mednafen running in GG mode (SMS palette on the right, TMS 50% on the left)

Zaxxon (SG-1000) SG2GG.ips (537 B)

Up at start-up to use the SMS palette, down for CV palette

Bomb Jack (SG-1000) SG2GG.ips (537 B)

Up at start-up to use the SMS palette, down for CV palette

Penguin Land (SG-1000) SG2GG.ips (537 B)

Up at start-up to use the SMS palette, down for CV palette

bsittler wrote

instead I'm inclined to first just try a couple that seem reasonable to me and see whether people are happy with them :)

whatever floats your boat is surely fine for me :)

bsittler wrote

if anyone has ideas for e.g. how to automatically pan to keep the player sprite onscreen in GG mode, that would be awesome!

I think it's impossibile. Beside that, I'm curious about why you're not seeing the whole screen - shouldn't the GG go in "SMS mode" (fullscreen)?

You can set it to GG mode in hardware and you get a "zoomed" view. I'm not sure if the scroll registers work in this scenario - it's likely they do - and so you could inject a routine to set them based on some game state regarding the player sprite location. But I suspect games will not be very playable like this.

sure the scrolling works, the matter is that how can 'automatically' follow the player sprite?
The best you can do is possibly to reprogram some games so that when you copy the SAT (and making sure you do know which sprite is your player!) you also update the scroll registers accordingly... (also, don't forget they're write only...)

sverx wrote

bsittler wrote

if anyone has ideas for e.g. how to automatically pan to keep the player sprite onscreen in GG mode, that would be awesome!

I think it's impossibile. Beside that, I'm curious about why you're not seeing the whole screen - shouldn't the GG go in "SMS mode" (fullscreen)?

The patches make the same game ROM work in both windowed (GG) and fullscreen (SMS) modes. This is possible because GG mode leaves a special fingerprint in some of the port-mapped registers. I did this because (a) games are sometimes playable windowed with centered viewport already (e.g. Zaxxon), (b) sometimes the only wiring available is for windowed mode, (c) on the original GG screen many pixels blur together with strange artifacts in SMS mode, and (d) because I'm optimistic that with scrolling hacks additional titles might work this way too.

Expanding on (b), some cartridges are only wired for one of those modes but not the other: for example, anything plugged through an unmodified Beeshu Gear Master is SMS only, and some GG flash cartridges hardwire GG mode, as do most regular GG game cartridges -- so using one of these as a donor PCB without modified traces will force GG mode. The only GG PCB hardwired to SMS mode I have (one of the Mickey Mouse series) is too nice a game for me to consider taking it apart and using as a PCB donor. Others, e.g. GG EverDrive, support both modes using special hardware inside the (GG) cartridge, and choose which to use based on file extension. AFAIK the mode is not changeable at runtime by regular GG or SMS software means, though, as it involves changed electrical connectivity between a couple of the GG cartridge pins that don't have equivalents on the SMS or SG-1000/.../MkIII pinout.

Maxim wrote

You can set it to GG mode in hardware and you get a "zoomed" view. I'm not sure if the scroll registers work in this scenario - it's likely they do - and so you could inject a routine to set them based on some game state regarding the player sprite location. But I suspect games will not be very playable like this.

I hope to find out soon whether this is actually possible. Another possibility might be manual adjustment using an vertical sync interrupt handler patched to intercept e.g. START+optional direction and use that to choose which part to center - START alone to re-center, the others for window positions flush with the appropriate edge(s) of the SMS screen.

sverx wrote

sure the scrolling works, the matter is that how can 'automatically' follow the player sprite?
The best you can do, eventually, is to reprogram some games so that when you copy the SAT (and making sure you do know which sprite is your player!) you also update the scroll registers accordingly... (also, don't forget they're write only...)

Right, I was assuming this would need to be a semi-sophisticated patch likely based on trial and error and/or disassembly of the specific game. My hope is that some of these games are old and simple enough to actually use a single sprite index exclusively for the player or other "focus" point, possibly making identification of the code to patch a bit simpler. Some emulators actually have an option like this already, e.g. smsadvance which is dealing with a screen without enough pixels in the vertical dimension. Needed VDP state being write-only complicates things significantly

edit: I tested some more using my closer-to-original Game Gear (the one with modern backlight but original LCD, no McWill screen) and I think that in SMS mode some games are a lot more playable using the higher-contrast "SMS" version of the SG-1000 palette rather than the "tms50+" palette, even though the colors of the "tms50+" one seem to be much closer to what the SG-1000 software I'm working with look "correct" with -- e.g. Bomb Jack and Zaxxon colors look closer to arcade RGB, and to emulator output for emulators actually claiming to emulate SG-1000 as opposed to SMS. Unfortunately the GG SMS display mode drops a lot of pixels so e.g. it's very hard to spot the "splash" when a Zaxxon test shot hits an approaching wall. For now I just start the game holding the up direction on the pad when using the non-McWill GG and booting the game in SMS mode, which makes things uglier but reduces the number of accidental wall collisions.

A very similar patch worked on a Retrode dump of the Othello Multivision Q*Bert cartridge; the original dump was 8096 bytes and had the MD5 a768a8ae921126300e98f9d918a4a0c9 but the patch converts it to 32768 bytes to make room for the palette patcher (and a whole lot of zeros in between which the IPS format compresses very efficiently)

For this game the default palette (more like SG-1000 than like the SMS approximation) seems to work better on all systems than the SMS one. Q*Bert actually ends up being fairly usable even in "windowed" mode on the Game Gear

QBert (J) (MV) (SG2GG).png (18.39 KB)

Q*Bert in mednafen in Game Gear windowed mode showing both palettes

Q-bert (Japan) (Othello Multivision) SG2GG.ips (545 B)

Press up during start-up for SMS palette, down for CV palette

You can extend to 16KB, or put the header at 8KB-16, it's a never used feature of the BIOS. But I guess nobody cares about 32KB nowadays :)

Maxim wrote

You can extend to 16KB, or put the header at 8KB-16, it's a never used feature of the BIOS. But I guess nobody cares about 32KB nowadays :)

Yeah, that is my hope - ROM/flash should be cheap enough in this era. I was concerned when I read that no known game uses the SMS header with that size and was concerned that it could trigger bugs so I inflated to a known-good size.

In fact I just got SG-1000 Chack'n Pop (both unmodified MD5 286ba24b335a1600dfc611a0a9fe7875 as trimmed from a Retrode2 dump, and with the English translation patch applied previously MD5 fb5c6e4d23b192cf36d87192289444e2) working by inflating further (to 48k) but for this one I left the header at 7ff0 and the header lies and claims 32k to avoid bugs

edit: I also got my dumps of SG-100 Wonder Boy (MD5 76f29fee0cd3af921e488a276dace636 - I'll warn that it's certainly no comparison to Revenge of Drancon, quality-wise!) and Championship LodeRunner (MD5 f49d9ea611ccb9289994774406f20d06) working, though the latter one unfortunately seems to actually use the BIOS header area so it will likely only work correctly in a no-BIOS early JP-model Game Gear. These patches likewise inflate to 48k

edit 2: turns out Chack'n Pop uses the BIOS header area too, as part of the released heart sprite. Zero out 0x7ff0 ... 0x7fff to fix the glitch (I'll upload fresh IPS files once I have a chance to generate them)

edit 3: Chack'n Pop is fixed (no more BIOS header, freed heart sprite no longer accompanied by graphical errors)

edit 4: Sega-Galaga is added (48K inflation); my Retrode2 dump is likely incorrect (truncated to 40960 bytes, MD5 17a97b16c3c7551c1d0bc98271d65dd1) but seems to work fine; this is another no-BIOS-header dump, so you will need to defang, remove, or otherwise bypass your BIOS (e.g. using a flashcart with BIOS-defeating ROM prior to the "real" ROM) to use this dump. Sega-Galaga does a really odd thing at start-up where SP is initially pointed at ROM(!) and then repointed at RAM, and my patch works by relocating the second SP setup inside the inflated area

edit 5: Removed separate patch for English translation of Chack'n Pop as it is byte-for-byte identical with the patch for the untranslated version

edit 6: Finally got a Retrode2 redump of Sega-Galaga (truncated to 40960 bytes with MD5 7f7e1d564448fdce96d239ad9ebf37d6) which seems to match what others have reported; the same patch works; only differences were some strange infrequent bit-errors scattered throughout the earlier dump

edit 7: Othello Multivision Guzzler (Retrode2 dump trimmed to 8192 bytes with MD5 f3f1042745e96e29bfdf920d031b8cd5) works too

edit 8: Space Invaders (16384 bytes inflated to 32768 bytes, MD5 87a97b049ec01b1803b93f06d0407586) and Star Force (32768 bytes inflated to 49152 bytes, MD5 2cbd1f9f4927f9618390340f56f116a6) are working now too, both with BIOS headers

edit 9: Three more 32K dumps patched & working with BIOS headers: Lode Runner (MD5 4b4f02eb3cf7d5f9dcd1311d72e6d742), Monaco GP v1.1 (MD5 74121fd6f1024ee3d3f5d1db29956d7d), and Sindbad Mystery (MD5 7b0f2be3588337df59959ababbefe505)

Chack'n Pop (SG-1000) SG2GG.png (20.79 KB)

Chack'n Pop in mednafen in Game Gear windowed mode showing both palettes

Chack'n Pop trans [v1.02] SG2GG.png (21.88 KB)

Chack'n Pop English translation in mednafen in Game Gear windowed mode showing both palettes

Wonder Boy (SG-1000) [!] SG2GG.png (19.68 KB)

Wonder Boy in mednafen in Game Gear windowed mode showing both palettes

Championship Loderunner (SG-1000) SG2GG.png (19.05 KB)

Champtionship LodeRunner in mednafen in Game Gear windowed mode showing both palettes

SegaGalaga-SG2GG.png (15.64 KB)

Sega-Galaga in mednafen in Game Gear windowed mode showing both palettes

Guzzler (Japan) (Othello Multivision) SG2GG.png (23.03 KB)

Guzzler in mednafen in Game Gear windowed mode showing both palettes

SpaceInvaders-SG2GG.png (16.65 KB)

Space Invaders in mednafen in Game Gear windowed mode showing both palettes

StarForce-SG2GG.png (21.54 KB)

Star Force in mednafen in Game Gear windowed mode showing both palettes

Lode Runner (JEK) (SG-1000) SG2GG.png (13.91 KB)

Lode Runner in mednafen in Game Gear windowed mode showing both palettes

Monaco GP (Japan) (SG-1000) (V1.1) (32K) SG2GG.png (14.93 KB)

Monaco GP v1.1 in mednafen in Game Gear windowed mode showing both palettes