melonDS aims at providing fast and accurate Nintendo DS emulation. While it is still a work in progress, it has a pretty solid set of features:

• Nearly complete core (CPU, video, audio, ...)
• JIT recompiler for fast emulation
• OpenGL renderer, 3D upscaling
• RTC, microphone, lid close/open
• Joystick support
• Savestates
• Various display position/sizing/rotation modes
• (WIP) Wifi: local multiplayer, online connectivity
• (WIP) DSi emulation
• DLDI
• (WIP) GBA slot add-ons
• and more are planned!







Download melonDS

If you're running into trouble: Howto/FAQ
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More camera trouble...
Jul 6th 2025, by Arisotura
So I had made a nice post about Let's Golf and how it was fixed...

But, obviously, as far as DSi camera support is concerned, it wasn't all.


I looked at another game that was running into issues with the camera: Assassin's Creed II. The Wanted feature in the menu uses the camera, if you're playing the game on a DSi, but on melonDS, it just showed nothing at all.

Quick investigation showed why.

Normally, when using the camera, games will set up the DMA with a block length of N scanlines, and a total length matching the length of the full camera picture. The DMA channel will also be set to trigger an IRQ when it's done.

However, this game does things differently. The DMA channel has no total length setting, and is just set to repeat infinitely. It transfers picture data to a small temporary buffer, from which the game reads when needed. No idea why they did it this way, but regardless, shows why it's good to emulate things accurately. Anyway, a NDMA channel that is set to "repeat infinitely" will trigger an IRQ after each block, but due to an oversight, melonDS never triggered any IRQ.

After fixing this, I did have the camera feed showing up in the game's UI thing, but it was rolling. Heh. Couldn't have been so simple.

This turned out to be because of the timings for the camera transfer. The timings melonDS used were a big fat guess, and were way too fast for that game.

I dug up my old camera test homebrew and modified it to track camera timings from the DSi. Took some time to figure out the logic behind the numbers I was getting -- there was more time between camera DMA transfers when running in 256x192 mode, than in 640x480 mode. In fact, it makes sense: internally, the camera always runs at 640x480, and the HSync/VSync are the same, but when told to output a 256x192 picture, the camera simply skips some of the scanlines.

... read more
4 comments (last by jiink) | Post a comment
Windows OpenGL issues fixed, finally!
Jun 28th 2025, by Arisotura
I went on a quest and battled the worst enemy imaginable.

Worse than a thousand orcs.

I fought endless privacy settings screens. Warded off all sorts of bullshit offers. Resisted the temptation to throw my brain in a lake.

I installed Windows 10 on my old laptop Crepe, so I could finally fix the issues with multiple windows and OpenGL.

CasualPokePlayer greatly helped me understand the problem, too.

Basically, due to the way melonDS works, when using OpenGL, we create the GL context on the UI thread, then use it on the emu thread exclusively. This is so that the OpenGL renderers can access OpenGL without needing extra locking. Window redrawing is also done on the emu thread.

The issue was due to how I originally implemented the multi-window mode. When a second window is created, it shares its GL context with its parent window. This way, everything OpenGL related will work on all windows. Except it turned out that the parent context was created on the UI thread, then made current on the emu thread, before the child context was created. Windows doesn't like that, and thus, fails to create the child context.

So it took some reworking to get this working smoothly, but the issue is fixed now.

This means that the proper 1.0 release will be soon -- for real. This issue was the last show stopper, basically.

... read more
13 comments (last by I have no ideas) | Post a comment
DSi bugfixes
Jun 24th 2025, by Arisotura
So, yeah... The current mood around melonDS is "it does most things pretty well already", as far as emulation is concerned. While it's certainly true for the DS side of things, there's still a lot to do with the DSi. And this randomly piqued my interest.

Notably, we still have a bunch of games that can't get ingame, generally hanging on something DSP-related.

So I took one of those games: Let's Golf.



When run for the first time, the game has you create a profile, by first entering your name, then taking a selfie to be used as a profile icon. All fine. However, here the game freezes before you can get to the selfie part.


So I dug into it to try and figure out why it was freezing. We knew it was trying to use the DSP, but not much beyond that... anyway, I extracted the game's DSP binary to get more insight. The DSP was just running its main loop, waiting for incoming commands. On the other hand, the ARM9 was stuck, waiting for... something.

The ARM9 was using the PDATA registers to read the DSP memory, however, that got stuck. The bug turned out to be silly: PDATA reads/writes can have a fixed length set, but the code handling them wasn't calculating that length correctly, so there wasn't enough data being returned. Hence the ARM9 getting stuck.

When fixing that, I could get to the selfie screen thingy.



... read more
6 comments (last by Arisotura) | Post a comment
Proper melonDS 1.0 release "soon"
Jun 21st 2025, by Arisotura
Apologies for taking so long to do a proper release.

Regardless, I think most, if not all, of the bugs that were found in the 1.0 RC have been fixed, so expect the proper 1.0 release soon. Hopefully.

The main issue would be the lack of functional Windows CI, but we're working on it...

We also have fun plans in mind for further releases, but we'll see once we get there.
8 comments (last by Jajanos) | Post a comment
Technical issues #2
Jun 14th 2025, by Arisotura
You might have noticed the lack of Windows builds on the nightlies page.

Sorry about it. The Windows CI is broken. Our CI expert Nadia has been on it for a while, so hopefully it should be back up again... someday.


On the flip side, the little loser stopped trying to take the server down, so that's atleast one positive.
3 comments (last by ded-doed) | Post a comment
Technical issues
Jun 8th 2025, by Arisotura
It appears that in the past days there have been resource usage spikes on our server. So either someone is trying to DDoS us, or the AI garbage bots are hitting our site.

I'm going to come up with a response to this, but in the meantime, there may be technical issues (like earlier, MySQL was down for some reason). Sorry about it.

Edit- we should be mostly good now. I thought it was AI slop taking us down, but it turned out to be a little moron spamming the board's search system with absurdly long queries. So yeah, problem solved.
14 comments (last by feen) | Post a comment
Small DLDI fix, and maybe more
May 26th 2025, by Arisotura
Mental health still complicated. Getting somewhat better...

I made a more personal blog, to post about other fun projects of mine (including the WiiU gamepad stuff) and other fun shit. If you're interested, it's here: https://arisotura.dreamwidth.org/


Anyway, I committed a fix to melonDS. May not seem like a lot, but after months of not touching the code at all, it's something.

Just today, I heard about a DLDI test program failing on melonDS, which piqued my interest.



I'd have thought DLDI was a solved problem, so this was interesting. What's going on there?


DLDI is a standard interface that was developed to allow clean support for different DS linkers. Since they all have different hardware interfaces and different ways to access their storage medium (CF or SD card), homebrew apps would need to embed drivers for each linker they intended to support, which would be quite a mess.

Instead, the homebrew itself only includes a DLDI stub, with a simple header and dummy functions. The linker's loader then patches the homebrew with its own DLDI driver when loading it: the DLDI stub is replaced with the linker's driver, which contains the adequate code for accessing the linker's storage medium. The driver contains some simple functions, like "initialize", "is the card inserted", "read sectors", "write sectors", etc.

melonDS implements DLDI in a similar way.

... read more
9 comments (last by Arisotura) | Post a comment
melonDS RC bugs
Apr 29th 2025, by Arisotura
The RC has lasted quite long, heh...

It seems that a recurring problem with it is that multiple windows don't work with OpenGL. The issue is that it seems to be a Windows problem -- I tested it on Fedora and it works fine (although there is another weird bug related to hiDPI scaling).

If you've paid attention to the window decorations on my screenshots, you've prolly seen it -- the last Windows I've been willing to use was Windows 7, but I use Linux now...

The aforementioned OpenGL issue is likely related to context sharing, so hopefully not a complex issue. I'd just need to install recent Windows in a VM of sorts, or have someone else do the testing and fixing.

I guess that's also why I'm less motivated by melonDS these days... my brain is all about the intellectual stimulation and challenge. I guess a lot of emudevs are like me too, it's more fun to go after emulation bugs or reverse-engineer hardware :P

We'll come up with a fix, though.

We always do.
22 comments (last by RoundCactusSM64) | Post a comment
Little news...
Mar 17th 2025, by Arisotura
Thank you all for the kind messages, it means a lot to me.

Things are still rough for me. On one hand, I'm dealing with old personal issues that I have never really addressed properly. On the other hand, I have been feeling very pessimistic about the state of the world and the future for years now, so that doesn't help. There's also surgery recovery playing into this, but that should hopefully get better with time. Anyway, I'm going to try a new type of therapy, since previous attempts haven't really helped.

As far as melonDS is concerned, there won't be much news from me for a while. I think I need a break from it. Sometimes it just feels good to focus on something else.

I could talk a bit more about the Wii U gamepad stuff, though. For now, I mainly post in threads at GBAtemp and nesdev, but I could make a kind of blog for it. I don't know... I intended to make a blog of that kind for it and other personal projects, but, you know, ADHD.

Anyway. The Wii U gamepad.

As you might already know, that gamepad is a nifty little tablet with its own processing power. It runs off an ARM9 CPU clocked at 108 MHz, with 4 megabytes of RAM. Okay, it's less powerful than the DSi, but there's something about running custom software on it that I like. It scratches a very particular kind of itch for me.

It's actually a little project I had started back in 2016, around the same time melonDS was born. Which resulted in some files for this project having melon-themed names too. Heh. Anyway, I was able to run some custom code on the gamepad, but couldn't do much beyond toggling the rumble motor -- the gamepad version of your typical 'blink a LED' embedded hello-world program, I guess. Lacking hardware documentation and proper means to upload and debug gamepad code, I was fumbling in the dark, and didn't get much done. I had made another attempt in 2022, but it also went nowhere.

Last year, I went for it again, but used a FPGA to replace the gamepad's SPI FLASH memory. In a more detailed post, I could go in details about how this was done and the clever tricks it uses, but long story short, this not only lets me easily upload code to the gamepad, but it also serves as a handy debug output.

This checkerboard pattern may not seem impressive, but it took a bunch of trial and error to get this to show up at all on the gamepad screen. This isn't the DS where the screens kinda Just Work(tm) and you can display basic stuff with some simple initialization. The gamepad requires you to initialize the LCD and video hardware before anything will be displayed.

... read more
28 comments (last by anon) | Post a comment
Sorry.
Feb 27th 2025, by Arisotura
I am completely burnt out.

Haven't touched melonDS in forever. Even with gamepad stuff, I'm slow.

My mental health is terrible.

Don't expect much news from me for a long while. As far as the proper 1.0 release is concerned... I don't know.

Sorry.
60 comments (last by Reual) | Post a comment
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