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
Audio interpolation
Apologies for the slow Summer! We don't have air conditioners in the melonDS HQ. The current climate is causing the team to slowly melt.

Anyway, audio interpolation is one of the emulation improvements that have been requested for melonDS. My general policy for emulation improvements is that they should allow for keeping the accurate code paths, and they shouldn't add too much complexity to the code. Audio interpolation is well within these bounds. Actually, I had implemented it in DeSmuME back then, and due to the way DeSmuME's mixer works, it was quickly done.

So I figured I would give it a try in melonDS.

The basic idea behind audio interpolation is to smooth out the audio samples as they're being upsampled. DS games may have downsampled audio to save on space and bandwidth, and the DS mixer doesn't perform any interpolation, which can lead to rough sounding samples. The reason the DS does no interpolation is most likely due to how its mixer hardware works, but obviously as an emulator we can ignore these constraints and do a better job.

It's also noting that, as far as melonDS is concerned, there are two parts we need to take care of: the DS mixer and the audio output.

In the DS, the mixer is driven by the system clock, like nearly everything else. If you ever coded for the DS, you might have wondered why the frequency registers for the audio channels are weird:

40004x8h - NDS7 - SOUNDxTMR - Sound Channel X Timer Register (W)

 Bit0-15  Timer Value, Sample frequency, timerval=-(33513982Hz/2)/freq

The PSG Duty Cycles are composed of eight "samples", and so, the frequency for Rectangular Wave is 1/8th of the selected sample frequency.
For PSG Noise, the noise frequency is equal to the sample frequency.

The SOUNDxTMR registers directly control the channel timers, which are driven at half the system clock. These work like the general purpose timers: they are incremented at half the system clock, and every time they overflow, they are reloaded to the SOUNDxTMR value and the channel advances to the next sample.

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Tragic news
[CONTENT WARNING: mention of suicide]

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Pride month and DMA timings
Well, happy Pride month, or whatever, dunno how to put it. As a trans girl of some flavor, I just want to reiterate support to the LGBTI+ community. I'm also not the only LGBTI+ member of the melonDS team, btw.

Now, let's talk about something more technical (so this post is not just a 'political statement' :P ).

DMA timings.

You might have noticed the timing17 branch. So what, another timing branch. Arisotura just loves these. Or something.

It's going to be some general timing renovation, depending on how far my motivation will take me. I started the work with DMA timings, figuring it would just be matter of taking into account that sequential timings only work when the address is incrementing linearly... well, it's hairier than that.

This is based on tests done at like 04:00, and this is the DS, so take this with a rock of salt.

Most memory regions in the DS have such timing characteristics that sequential accesses make no difference, atleast from the standpoint of DMA. The ARM9 and its 3-cycle penalty when using the bus are another story.

However, there are a couple regions that have different rules.


Main RAM (0x02000000)

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Well, guess we owe you another release soon
A quick 0.9.3 release would be welcome, especially to fix the stupid bugs that appeared in 0.9.2.

Like how touchscreen input will wrap around instead of properly clamping like it's always done. This is a good reminder to us to always test all features, even those that are granted for working. They work... until somebody introduces broken code that breaks them. It's not like this hasn't happened in the past, either, so we should do more quality control.

Sorry about this.

I haven't been doing a whole lot of melonDS coding lately either. I began researching some issues, began working on timing test suites, then veered to MPU stuff, and, well...

There are other things going on in real life, which doesn't help. I can't really focus on more than one big thing at once. There are a few going on right now: trying to find a bigger apartment to move in with friends, another housing-related thing I can't really post details about, and dealing with the obnoxious little pricks who live right next to my apartment and like partying all the damn time. Seriously they look like kids who got a fancypants sound system for Christmas or something.

Once these things have settled I will hopefully be able to work more on melonDS.

The first test suites I was making were for DMA timings. I'd need to polish them and add more test cases to make it good. Although really, the timings mostly boil down to a set of rules, some of which I have yet to implement into melonDS: for example, the maximum length of a sequential read/write burst is 118 units, and (figures) sequential bursts only work when the address is incrementing. The main issue I face is implementing the rules in an elegant and efficient way.

This doesn't even get into the fun part of CPU timings. You get the code fetch cycles, data access cycles, and other internal/etc cycles, which may interact and overlap in all sorts of fancy ways.

I want to address the timing issues once and for all, and I feel it's pointless to attempt things like full cache emulation if our underlying timing model is wrong.
Introducing the compute renderer
To make things short, I've been working on porting melonDS's software rasteriser to run on the GPU via compute shaders. So how is this different to melonDS's existing OpenGL renderer? The OpenGL renderer uses builtin functionality of your GPU to draw triangles. This is of course fast, since it uses hardware specifically made for this, but it has the downside that some things can't be controlled by us, so the behaviour of the DS can't be replicated completely faithfully. On the otherhand this only utilises the programmable parts of the GPU (which means we have full control over them), so it's like the software rasteriser, only it utilises the parallel computing power of GPUs. Ideally it should be eable to be just as accurate as the software rasetriser is.

Why are we doing this in the first place?
  • Enhancements such as higher resolution rendering at reasonable speeds compared to say a software rasteriser, but with less problems than the OpenGL renderer (though problems can never be fully excluded when running games differently than they were intended).

  • Fullspeed emulation of 3D games on Switch and potentially other devices which fit this weird niche where they have slow processors but pretty competent GPUs and good software side support for it.

You might have already heard of parallel-rdp from Themaister which provides a very accurate emulation of the RDP (i.e. that part of the N64 which in the end draws the triangles) running on the GPU. It has been a great inspiration for this project (which means where possible it's basically a clone). So thanks to Themaister for all the ideas and also for answering my questions!

Currently the main part of the work is done (it's already somewhat playable with a lot of games), so it's easier to list what's still missing:

  • Blending

  • Shadows

  • Equal depth testing

  • Antialiasing

  • Highlighting/Toon shading

  • Fog

  • Edgemarking

  • Rearimages

I plan on detailing some technical aspects later. Also I have not forgetten my A tour through melonDS's JIT recompiler "series", so expect to see some more posts by me here sooner or later.
melonDS 0.9.2 is out!
This release brings some welcome changes.

Namely, improved Mac support: there have been fixes to the JIT, but also to the interface, so things should work more smoothly under macOS.

melonDS also supports loading ROMs from the most common archive formats, now, which means users with large ROM sets should have it easier.

We also have a new menu listing the ROMs you have opened recently, making it quicker to open them again.

We got new fancy screen modes courtesy Generic. These make it possible to use 16:9 hacks along with melonDS, among other fun things. Speaking of renderers, he also went and fixed a whole bunch of OpenGL issues.

The cart interface refactor was finished in time for this release, and with it, support for NAND save memory. WarioWare DIY and Jam with the Band are now able to save correctly under melonDS.

And, as usual, there are a bunch of other misc changes, which you can find about in the changelog or commit history.

Enjoy!


melonDS 0.9.2, Windows 64-bit
melonDS 0.9.2, Linux 64-bit
melonDS 0.9.2, Linux ARM64
melonDS 0.9.2, MacOS 64-bit
melonDS 0.9.2, MacOS ARM64
melonDS 0.9.2, MacOS universal
Change to the save file handling
I continued the work on the cart_refactor branch, and the structure itself is nearly done (I'll still need to take care of savestates). And, in a typical burst of ADHD-coding, I went and implemented support for NAND save memory, as used by WarioWare DIY and Jam with the Band.

This is when I realized that the current way melonDS handles save files was going to be problematic. Basically, if a save file already exists, melonDS will determine the save memory type from that file's size, instead of using its built-in game list. This was designed in the old days, where we had some wonky heuristics instead of the game list -- the basic idea was that if melonDS failed to determine the correct save memory type, you could provide a known good save file and it would work, bypassing the problem.

Obviously, this is also a double-edged sword. If you happen to have a save file that isn't the correct size, melonDS will pick the wrong save memory type, potentially breaking things. In the end, this strategy now seems to cause more problems than it solves, especially since we have the game list.

The NAND thing was the final nail in the coffin of this strategy. It had been assumed, from some source I don't recall, that the save memory size for NAND was 32MB, and this was nice, because each possible save memory size had only one associated type, no confusion. However, the hardware tests I did showed that the NAND save memory is actually 8MB, and this conflicts with one of the possible FLASH sizes.

(EDIT- I was corrected by another tester. The save memory for WarioWare DIY is 16MB, not 8MB.)

So I ripped the old thing out, and instead made it always rely on the game list to determine the save memory type, regardless of the save file's size. As a bonus, save files that are too big will work too, melonDS will just ignore the extra contents. Which means that, for example, DeSmuME's .dsv files could be used as-is, by just changing the extension to .sav.

If you believe this is going to be a major disadvantage, or see any issue with this, I encourage you to reply to this post.
Redesigning the cart interface
The kind of change that doesn't immediately mean a lot for end users, but means a lot for us coders (and ultimately means something for end users, too).

Anyway, this tends to show why it's good to think forward when designing your code. That being said, I need to find a balance with this. I tend to either think forward too much and end up paralyzed by questions that don't mean much, or just write code as it comes to my mind.

The cart interface in melonDS was originally built without much consideration for future. If you're wondering, the cart interface is the part of the emulator that lets emulated software access the emulated cartridge, because on the DS the cart isn't just directly mapped to CPU address space like on older consoles. Instead, there are a bunch of commands you can send to the cart to retrieve various parts of the contents, and different encryption protocols securing it up.

As melonDS became capable enough to run commercial software, emulating the cart interface was a must. So NDSCart.cpp was born. The main component is the NDSCart namespace, which originally emulated the cart interface hardware (basically the DS side) and command responses for a generic cart. There is also NDSCart_SRAM, which emulates the on-cart SPI save memory. A tad hacky, but for most games, it did the job.

But, that's the thing, not all DS carts are the same!

There were already some exceptions for homebrew ROMs, which might want to use the cart interface and, depending how old they are, need a more lax implementation of the generic cart protocol. Namely, retail carts don't let you read addresses lower than 0x8000 via the generic data read command (0xB7), because that region contains the ROM header (read via a different command), the Key1 encryption data and the secure area. However, old homebrew ROMs don't have any of that (save for the oldstyle DS header), and have their ARM9 binary start at 0x200. Newer homebrew ROMs are closer to the layout of a retail cart, mostly due to the added DSi support (the DSi header is 0x1000 bytes instead of 0x200), but, since not everybody is here to rebuild their ROMs, we still need to support the older ROMs.

Homebrew aside, there are also different types of retail carts.

A prime example is Pokémon games. The carts are fitted with a IR transceiver, which is accessed via the save-memory SPI bus. In practice, the first byte of a SPI transfer is a command for the IR transceiver. For now, we know that command 0x08 is some ping command that should reply 0xAA, and command 0x00 is the pass-through command, where any further bytes are forwarded to the save memory. Emulating this is required for Pokémon games to be playable at all. In melonDS, these commands were added to the generic save-memory code. A bit of a hack, since this means these would be 'functional' in any game instead of just Pokémon games, but it did the trick.

But there's more. Games like WarioWare DIY, or Jam with the Band, don't even use the save-memory SPI bus. They have save memory, but it's a NAND memory that is accessed via the same bus as the ROM itself, through a set of specific commands.

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Release 0.9.2 coming out soon
As title says. Right now, the only thing holding us back is that we need to setup Azure CI for proper Mac builds. I have contacted the Azure service to get a CI grant, but they haven't gotten back to me yet.

We have some cool ideas, too, but these will be for further releases.

Also, in somewhat related news, I'm starting to work on another idea. It's not related to melonDS, but it's related to the DS. For now, this is going to be a surprise, but those who have seen my Twitter lately might figure out what I'm up to. I will make a post once I've got a working prototype.
Status updatezorz!
This is the first time I write a blog post in a while, so I will try to keep this short.

First, what's new on my side?

I finished my hearing for the gender marker change thing. You know, so I can get a big fat F on my ID card. You prolly don't care a lot about my trans shenanigans but this means it's one thing out of my way, and we can now proceed to full-speed melonDSing (and hopefully not from a squat, but we're doing our best).

What else is there to say?

I can't keep my focus on one thing aaaaaa

I wanna maaaaaybe try to emulate some new fun shit in melonDS. like the pokémon keyboard thingy.

Wait, no, we need to make DSi emulation better. We can prolly add a file explorer thing, so you can put your DSiware into the thing easily, and idk what other cool features there were. Just suggest them below this post, pretty sure we can get this done together! melonDS will soar through union and friendship!