iiinova — where your digital self keeps evolving

Plutiedev @plutiedev.com · 16/08/2026

Something tells me that the extended resolution for PAL in Streets of Rage was tacked on at last minute (look at the bottom side of each screenshot).

Streets of Rage title screen. The character sprites don't line up with the bottom of the screen and cut off at different points (and none of them touch the bottom border).

Streets of Rage character select. Mostly works but there's a visible black border at the bottom because it's not centered.

Start of round 1, the only part that actually looks correct because they extended the background to cover the extra room.

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Plutiedev @plutiedev.com · 30/03/2026

Peripheral ID 0x0E is still one of the biggest mysteries.

input a6.l = controller port address; output d7.b = $00 modem, $0d = Mega Drive Joy Stick, $0e = Ram Disk, $0f = ETC. or None; use d0, a0

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Plutiedev @plutiedev.com · 26/03/2026

Amusingly they "undid" that in Sonic Jam, it uses NBG0, NBG1 and sprites (NBG2 and NBG3 are unused). Besides pause menu can't show up here anyway. Leaves me wondering how they handled planes. My question was more why they didn't use NBG3 to avoid "window" and pause menu sharing the same layer.

Screenshot of the Data Select screen. It has a bunch of vertical-shaped slots for each file (and a smaller square one labeled "No Save"). For the larger slots, it shows a level icon ("New" since they're unused) as well as the selected characters (Sonic and Tails). There's a red frame around the selected slot, as well as arrows indicating you can change the character. The background is a low contrast Sonic. At the bottom there's a text saying "Data Select".

NBG1: the frame with the slots for the files, as well as the level icon ("New" in this case) and "No Save" label.

Sprites: the characters, the cursor, and the "Data Select" text.

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Plutiedev @plutiedev.com · 25/03/2026

They rewrote the effect so the platform is on another layer (instead of splitting the foreground in two through scrolling) but the platform is now on the pause layer so it sits on top of everything (oops)

NBG0 layer: the part of the Death Egg the platform was attached to.

NBG1 layer: the dark sky in the background.

NBG2 layer: pause menu and the platform.

Sprite layer. Don't mind the garbage (I used debug mode to place some monitors).

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Plutiedev @plutiedev.com · 25/03/2026

For whatever reason in the Sonic Jam version of Sonic 3 (NOT the original) the HUD gets hidden for a moment when the platform detaches from the Death Egg. 1:09:39 youtu.be/CVZcCK0skLY?...

Sonic is looking up on the final boss platform as the Death Egg detaches. The left side of the platform is covering the I in "rings" as well as the "Sonic" and lives count at the bottom left (but not the icon).

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Plutiedev @plutiedev.com · 14/03/2026

Apparently whoever designed the syscalls had the same idea as me (treat IRQ2 as a way to get the Sub CPU's attention rather than only as a way to pass vblank timing) Does the Sub CPU BIOS use it for anything beyond the user call timing?

Triggers INT2 on the Sub CPU via the IFL2 bit (for this reason, it should be called during VBLANK). Also syncs the COMCMD cache values to the GA registers and the COMSTAT values from registers to the cache.

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Plutiedev @plutiedev.com · 14/03/2026

It has VDP and joypad routines (and even routines for the communication ports), it's more of a BIOS than the Sub CPU one lmao Calling it Main CPU BIOS probably makes sense (also to set it apart from the rest of the boot ROM).

To be pedantic, "Main BIOS" is somewhat of a misnomer here. A more accurate term may be "Boot ROM System Library", and indeed for a while in Megadev we prefixed these calls with "bootlib". However, we eventually decided to go with "bios" as it is shorter and there is a symmetry to having a bios on both the Main and Sub side. Moreover, the entire internal ROM is very often colloquially called "the BIOS" especially in terms of emulation.

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Plutiedev @plutiedev.com · 16/12/2025

Took a quick look at Body Count and looks like they changed the Sega Mouse with the Mega Mouse, as expected from the region (yes, US mouse is "Mega" and non-US mouse is "Sega", they got it backwards). Also that's definitely Not Bruce Willis™.

Screenshot of Body Count device select screen. There's a guy who looks like Bruce Willis in the background holding a gun. Text: Player 1. Two icons at the bottom: 3 button controller (not selected), European Sega Mouse (selected). The mouse is square-ish and has two blue buttons separated by a small gap.

Same as the other screenshot, but the Sega Mouse has been replaced with a Mega Mouse. This mouse is a lot rounder, has three normal buttons + a small Start button below, and there's no gap between those three buttons.

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Plutiedev @plutiedev.com · 16/12/2025

This is going to go underreported but Garfield The Lost Levels replaces the password and bonus round options with one that lets you watch several of Garfield's animations.

Original options menu. Garfield. Difficulty: kitty (selected). Password. Music: 01. SFX: 001. Bonus Round. Exit. To the left of the title is Garfield looking tired (from having to push in the title when you enter the menu).

The Lost Levels options menu. Garfield. Animation: (no text after the colon, selected). Difficulty: kitty. Music: 01. SFX: 001. Exit. Garfield is to the left of the title, looking like he's climbing on something because we're playing that animation.

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Plutiedev @plutiedev.com · 16/12/2025

I was wondering what were the changes in the Sega Channel version of Bloodshot (er, Battle Frenzy) and it didn't take long to find.

Screenshot of the walls in the first room. The texture is incomplete and half of it looks like a glitchy mess.

Screenshot of the same room, with the texture fixed.

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Plutiedev @plutiedev.com · 15/12/2025

So the Sega Channel guide in Argentina and Chile was bilingual, huh? (I assumed it'd stick to one language, not offer both)

Sega Channel Game Guide. To return to Now Playing, Please reset your adapter. VRC Ratings/Clasificaciones VRC. Game Categories. Gameplay Help. Accessories. Troubleshooting Guide. [Spanish ahead] Categorías del juego. Ayuda en el Sega Channel. Accesorios. Guía para corregir problemas.

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Plutiedev @plutiedev.com · 08/11/2025

Also funny you mention downloading games since their original idea was to let you download games *to floppy disks* mdshock.com/2018/07/08/t... (that never panned out, of course)

Modem. Sega has put a lot of effort into researching network gaming, but that would be out of the question without a modem. If you are worried about cost, it appears that Sega is going to sell its high performance modem for an unprecedented low price. The modem will allow you to play games in real time with distant friends. In addition, Sega will eventually offer new games which can be downloaded onto floppy disks using the modem, so you can avoid the nightmare of waiting in line for new releases.

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Plutiedev @plutiedev.com · 07/11/2025

Today in YM2612 instrument serendipity:

A waveform that looks like mostly quiet noise with two small spikes and then one large glitch spike, repeated over and over.

YM2612 parameters for this instrument. MUL: 0, 0, 0, 0. DT: +3, +3, +3, +3. AM: off, off, off, off. TL: 26, 127, 127, 0. SL: 0, 0, 0, 0. AR: 31, 0, 0, 31. DR: 0, 0, 0, 0. SR: 0, 0, 0, 0. RR: 15, 15, 15, 15. KS: 0, 0, 0, 0. SSG: off, off, off, off. Feedback: 7. Algorithm: 2. Note: C-4. LFO: off. PMS: 0, AMS: 0. Help labels: A/C: edit, D-pad: select, B: play.

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Plutiedev @plutiedev.com · 04/11/2025

If there's a constant about Sonic 3, it's that the barrel will keep trapping players who don't know the trick to get past it.

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Plutiedev @plutiedev.com · 03/11/2025

Virtual Lab for Mega Drive www.plutiedev.com/blog/20251103

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Plutiedev @plutiedev.com · 03/10/2025

Nope, besides every level palette is guaranteed to be referenced directly because their address would be included in the level header.

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Plutiedev @plutiedev.com · 02/10/2025

Uh, is this palette in Sonic 3D used anywhere? I can't find any references to it (address is $0250E2, right after Sonic's palette) Absolutely sure that it's a palette because it's sandwiched in the middle of the LONG list of palettes that are used in the levels.

Palette that goes from black to orange for 10 colors, then light gray to dark gray for 6 colors.

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Plutiedev @plutiedev.com · 18/09/2025

You can't have the FDD and MCD at the same time, sadly. You can grab a Sega AI keyboard and paint it black for the aesthetic at least, I don't think you can plug it though :P

Photo of the unreleased Mega Drive keyboard.

Photo of the Sega AI keyboard, which looks nearly identical aside from being white instead of black and the blank key being an "AI" key.

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Plutiedev @plutiedev.com · 09/09/2025

Whose mother did I insult this time?

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Plutiedev @plutiedev.com · 27/08/2025

This kind of stuff is why it takes forever to figure out how the VDP works from the reverse engineered verilog (ironically, there's usually less going on than it looks like).

"In viewport" area check. PLA V: end of viewport inverted (l170), undo the NOT (w457), merged with VDP reset to force on if reset (w458). PLA V: start of viewport (l172). Viewport enabled? vertically (t38), =0 by w458, =1 by l172. PLA H: end of viewport (l137), merge with reset to force on if reset (w392). PLA H: start of viewport (l130). Viewport enabled? horizontal (t29), =0 by w392, =1 by l130. Display enable? (reg $01 bit 6) PLA V: line 511 (l162). Status port VB flag (w439) from l162 and display enable, goes to status port VB flag; NOT to get active scan (w466) to PLA table. In viewport area? (w389) from t38, t29 and display enable; delay by 8x hclk2 (l616), pick timing (w1075) mode 5 = l616, mode 4 = w389; delay by 3x hclk2 (l618), to w1068 (layer mix logic). In viewport area? (w388) from t29 and w439. Delay until next hclk2 (l417), again (l470), pick timing (w821) mode 5 = l470, mode 4 = w388; to w811, w812, w820, w822, w823 (sprite render logic). Delay w388 until next hclk2 (l512), delay again (l513), high to low transition (end of viewport area) (w850), delay until next hclk2 (l514), To w841, w842, w877 (sprite render logic). *w388 and w389 look like they may be practically the same at first, but the main difference is that w389 does not include line 511 as part of active scan, while w388 does include it.

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Plutiedev @plutiedev.com · 11/05/2025

I suppose this also means that not many people know that the piece used for the puzzle mode is also dropped as a normal piece from level 30 onwards, right?

Screenshot of Sonic Eraser from much later, at level 30 and score 307200. There's no Sonic here, but the unusual thing is that the piece with the stick and ring that normally only appears in puzzle levels is now in the grid.

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Plutiedev @plutiedev.com · 11/05/2025

How you can tell that I'm the only person who bothers to play Sonic Eraser: tcrf.net/Sonic_Eraser

Screenshot of a portion of the Sonic Eraser article on TCRF. Unused Sprites. Sonic Eraser. Artwork: (keep reading) Description: Sprites of Sonic running upwards, pulled from Sonic 1.

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Plutiedev @plutiedev.com · 03/03/2025

Fun fact: Sonic 3D doesn't have a 50000 points time bonus because they don't expect you to beat any act under 30 seconds. Anyway, beat Volcano Valley 3 in 27 seconds (and Spring Staidum 3 in 31, could have done faster there too if I paid more attention)

Sonic got through act 3. Time taken: 0:27. Score: 1900000. Time bonus: 10000. Ring bonus: 900. Total: 0 (it didn't count the tally yet).

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Plutiedev @plutiedev.com · 01/03/2025

This tweet is too good to let go x.com/tanglewoodga...

Tanglewood (@tanglewoodgame)
Shout out to our test bench Mega Drive. Over 3,000 cartridge insertions in the last two weeks, dropped regularly, accidentally had a 50v PSU plugged in, and has just survived its third coffee spill to the motherboard. Still running flawlessly. These things are built like tanks.
4:07 PM; Mar 8, 2019

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Plutiedev @plutiedev.com · 28/02/2025

Huh, found a couple of misplaced rings near the end of Diamond Dust 2. It's easier to see in Director's Cut but they're there in vanilla too.

A section near the end of Diamond Dust 2 from Director's Cut with the camera pointing far into the wall, you can see two rings seemingly floating in the wall, including shadows in the air.

Same area from the original game, one of the rings is barely visible in the corner. You can see the ice turret from right before the big ring floor.

The area with the rings, using the level editor. It's entirely wall (including snow floor, which you can't walk on), the rings and their shadows are somehow seemingly floating on a corner in this area.

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Plutiedev @plutiedev.com · 15/01/2025

What the waveform looks like if you wonder (apparently I can't mix a video and an image in a single post)

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Plutiedev @plutiedev.com · 15/01/2025

This is not what I had in mind…

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Plutiedev @plutiedev.com · 17/12/2024

I heard rumors of a service called X-Mail coming soon, I wonder if this is it?

XBand menu with four icons: X-Mail, Bandwidth, XBand News, Return.

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Plutiedev @plutiedev.com · 10/12/2024

Trying to trace the SG-1000 hardware family, I may have missed stuff or gotten something wrong. Note that these aren't necessarily backwards compatible, just derived. (dotted line = add-on)

SC-3000 is derived from SG-1000 (with the SK-1100 add-on). SF-7000 is a SC-3000 add-on. Master System is derived from SG-1000. Mega Drive is derived from Master System. System E is also derived from Master System. Teradrive is derived from Mega Drive and IBM PC/AT. Mega CD is a Mega Drive add-on, Mega LD is derived from Mega CD. Pico is derived from Mega Drive, Copera is derived from Pico. 32X is a Mega Drive add-on, Picture Magic is derived from 32X. Mega Tech is derived from Mega Drive, which in turn led to Mega Play. System C is also derived from Mega Drive.

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Plutiedev @plutiedev.com · 08/12/2024

I thought that YouTube had just added overshooting the scroll because it's common in mobile but turns out it's Firefox (even the Plutiedev site does it even though I added nothing)

Screenshot of the Plutiedev home page, the text is starting about halfway through the screen because of being pulled down.

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Plutiedev @plutiedev.com · 18/11/2024

New Solitaire win animation just dropped.

The screen fully covered in cards facing up.

The screen being covered by cards facing down too.

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Plutiedev @plutiedev.com · 20/02/2024

The water slide has no collision in this corner. (used debug mode to make it easier to get there for the screenshot but it's doable without it)

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Plutiedev @plutiedev.com · 20/02/2024

"How underused is the VRAM in special stages?" "Yes"

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Plutiedev @plutiedev.com · 18/02/2024

Today in weird things: if you roll into the block, you'll keep pushing it while rolling (Sonic won't stop). 今日のおかしいもの：ブロックに転がったら転がってる中で押してる（ソニックがやめない）

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Plutiedev @plutiedev.com · 15/02/2024

Huh, I didn't know that the Telegenesis had a logo all this time. メガドライブFAN vol.1 page 40

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Plutiedev @plutiedev.com · 15/02/2024

メガドライブFAN vol.1 (page 44)

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