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
• (WIP) GBA slot add-ons
• and more are planned!

Download melonDS

If you're running into trouble: Howto/FAQ
Refactor underway
Due to the scope of the refactor, keeping it all in a separate branch will not be feasible. I will have to merge my branch soon (hopefully by the end of the week).

This means that while the refactor is in progress, CI builds will be more or less rather broken and unstable, so don't rely on them.

We also plan on putting up 'beta' builds with certain features of interest, namely the compute shader renderer that has been merged recently, or season2 (the experimental LAN/netplay branch).

Also, side note: the comment section is not for posting your brainfarts. Pointless comments will be deleted. Repeated pointless comments will get you banned.

Thank you.
A couple notes about the Delta release
It appears that the recent release of Delta on the Apple app store is giving us extra attention. While this is nice, I would like to state a few things.

First, we the melonDS team are not responsible for third-party ports (with the exception of Generic supporting the Switch port, since he made it). Our scope is limited to the melonDS core and the desktop frontend (ie. the Windows, Linux and macOS versions).

If you are running into issues with Delta, or with any port of melonDS: you should contact the authors of that port. Members of our community may also be able to help you, but contacting the port authors directly may be quicker.

It is also worth noting that port authors are responsible for keeping their port up-to-date.

At the time of writing this, Delta is using melonDS 0.9.1 as its core, which is quite outdated by now. If you're running into emulation issues with Delta, chances are that the bugs have long been fixed, but you will need to bug the Delta authors to update their port. We have tried to contact them about this, but haven't received a response yet.

tl;dr: if you are running into any issue with Delta, or any melonDS port, please ask the authors of that port first.

Second point, emulation frontends like Delta, RetroArch or BizHawk (to name a few) are definitely impressive pieces of work, but it is worth keeping in mind that they wouldn't be possible without the work from the emulator authors who provide the cores these frontends use. So if you're considering donating towards these frontend projects, try to keep the underlying emulator core projects in mind too.

That being said, we have already seen an influx of new patrons, so thank you folks!

Third point, not related to Delta per se, but this is prompted by the situation: I'm planning a bunch of updates to the site.

... read more
News of the great refactoring
In this post I showed an attempt at running two melonDS windows at the same time. Just a silly test, but groundwork for more.

What became apparent during this is the fact that our current configuration system won't do.

The current config system was born out of simple needs: at the time we just needed to store a few configuration values. The keyboard and joystick input mappings, and misc settings like direct boot or 3D renderer threading. For this, a simple pseudo-INI format was deemed enough. The config file is named melonDS.ini, but it is just a simple key-value pair format with a custom parser, not an actual INI format.

The configuration data in melonDS is just a bunch of global variables in the Config namespace exposed to the entire program. The parser simply goes through all the lines in melonDS.ini, checks the key against a list of possible keys, and when a match is found, the corresponding variable is filled with the value that was read. The same list also serves to initialize the config data with default values (for example, if melonDS.ini wasn't created yet). All fine and dandy.

This system, however, doesn't shine in its flexibility. This started becoming apparent in 0.9.5 when the new local multiplayer system was added. I realized we needed a way to allow each melonDS instance to have different settings for things like input mappings. Prior, the only way to do that was to run the different instances from different folders.

The solution I had come up with, was to create other melonDS.ini files: melonDS.2.ini for instance 2, melonDS.3.ini for instance 3, and so on. melonDS.ini would contain the bulk of the settings: the settings that are common across all instances, and the settings for instance 0. Then, when opening a new instance, it will get the global settings from the main melonDS.ini, and its instance-specific settings from its specific config file. If said specific file doesn't exist, it is initialized from the main melonDS.ini.

It's nice and colorful, but a bit unwieldy...

When I started working on that proof-of-concept multiple window thing, I had a realization in the same vein. Basically, the config file also serves to store settings related to the window: size, layout settings, etc. For a multi-window feature to be useful, we want each window to have its own settings (say, having one window display the top screen, and another the bottom screen). Clearly, the current config system won't do here.

So what can we do? Find other creative ways to get around the lack of flexibility of the pseudo-INI system?

... read more
Wifi fixes: channels and power
Long time no update. Sorry about that. I'm getting better, though.

Anyway, I recently felt like getting back into melonDS dev. I figured that trying to fix some wifi bugs could help me build up momentum and motivation I'll need to finish the big refactor.

The point of the big refactor is to lay groundwork for turning netplay from a clunky proof of concept into an actual finished product. But netplay or LAN won't be very useful if the underlying wifi implementation is malfunctioning...

The first bug I looked at was that weird bug in Meteos: when starting a download play game, if you're using a DSPhat firmware, you will instantly get a connection error, but everything will work fine if you're using a DSLite firmware.

So I researched the bug, but the outcome was a bit disappointing. Long story short, it's a timing issue. The ARM9 starts wifi initialization and allows it about 44 milliseconds before deciding it has failed. The wifi initialization doesn't actually take this long, but on a DSPhat (or any console equipped with a type 2 RF module) the RF initialization includes an extra delay of 40 milliseconds. Changing the ARM9 cache timings fixes the bug.

Cache emulation is something we're looking at for the next release, as it may fix quite a bunch of these timing issues -- there have been preliminary tests and it's looking promising. But in the meantime, that particular bug goes beyond my scope.

No biggie, we have a plethora of other problematic games. In particular, I had gen4 Pokémon games in mind. In these games, players can meet into the Union room where they can decide to chat, battle, etc... but the Union room was said to be malfunctioning in melonDS if more than two players were in it.

I first ran into some 'easy' bugs. For example, melonDS would not generate different MAC addresses for extra instances when using an external firmware. I also had to obtain different savefiles -- the game will get confused if multiple players using the same save file try to connect.

Past that, I figured that the issue might be caused by the lack of wifi channel support in melonDS. You probably know about wifi channels: the 802.11 standard specifies a set of 14 channels, which correspond to specific frequencies.

... read more
Quick news

This is just a quick attempt at supporting multiple windows. There's still a whole pile of issues to fix, but it's looking promising so far.

This is not only part of the ongoing refactor, but would also pave the way for separate windows, a feature that has long been requested.

I'm having a bit of a question there: if we got multiple windows, which one should have the OSD? The main window? The currently active one? All of them?

Other than that, sorry for the lack of updates lately. January has been rough for me, but things are getting better. I've also been caught in a fun side project that involves reverse-engineering (and emulating, heh) ancient FPGAs. Maybe I could have a sort of personal blog for non-melonDS projects of that kind, or just personal stuff in general.
Merry belated Christmas
(to those who celebrate, that is)

As I have received and set up my new laptop, I've been able to work on melonDS some. The goal is still the same: to adapt melonDS for supporting multiple instances within one process.

The frontend is proving to be tricky, because it was largely built without many regards for code quality. Originally, the frontend was just quickly built around the program entry point in main.cpp, as it just needed to provide a means to use the emulator. We had a simple window, a dedicated thread to run the actual emulation, and that was it.

Obviously, over time we added various features to the emulator, rebuilt the frontend around different UI toolkits, piled on more features, and so on. Basically, the frontend code became a mess, and everything was more or less just dumped in the global namespace -- there are some modules which live in their own namespaces, but it's all not very modular, and doesn't lend itself to running multiple instances of melonDS.

I started by splitting main.cpp into separate files. We are far from done with the cleanup, so there's a lot of cruft around, but the basic idea is the following:

* main.cpp just holds the entry point (main()) and global application-related stuff.

* Window.cpp holds the MainWindow code, for managing the emulator window. We may also add support for multiple windows.

* Screen.cpp holds the ScreenPanel code, that is, the panel widget that goes inside the emulator window and handles display and touchscreen input. There are two kinds of ScreenPanel: one that relies on Qt's graphics API, and one that uses OpenGL.

* EmuThread.cpp holds the emulation thread.

... read more
Long-due status update
Sorry for the lack of updates lately. Mental health has been rough. Hopefully it's going to get better with the Christmas holidays...

What's new since the last post? I had started working on refactoring the melonDS codebase for the ambitious changes to come. JesseTG mostly finished the work on the core, so that's one big thing out of the way.

The frontend code is now going to need adequate refactoring too. That's, well, more work. We'll get there over the coming days.

On my side, I (finally) ordered a new laptop, so I'm waiting to receive it and set it up before I do more big work on melonDS.

I will need a while to adjust to the new changes that have been done to the melonDS core. It's also likely not perfect, we will likely have to do more work to clean up and harmonize the codebase. But atleast, the biggest part of the work is done.

On the frontend side, we need to add support for multiple different emulator windows. Historically, the frontend was structured around one emu thread and one emu window. The latter provides a means to display the emulator's video output and lets the user interact with the emulator, the former feeds the inputs into the melonDS core, runs it and manages it.

It wouldn't be difficult to spawn multiple emu threads, one per emulated DS. Window management is another deal. We thought we might want to support attaching multiple windows to one emu thread, for example to support displaying each DS screen on a separate window. For netplay purposes, we might also want to support headless instances, that is, running an emu thread with no window attached, no sound output, and inputs received from the network.

This also poses the question of OpenGL context management, all things we will need to look into.

We'll get there. It just... takes time.
Happy birthday melonDS!
Today melonDS is officially 7 years old. To celebrate, like last year, have a new version of the melonDS icon, recolored to the same orange color as 7 itself:

(if you're wondering about these colors: I have synesthesia, that's all)

I'm sorry for the lack of new releases since 0.9.5. It's been one year. That being said, we have big plans for the next release. I'm not going to go in length about these, the previous posts detail the plans well enough.

Just bear in mind that we're currently refactoring the melonDS codebase, so things may get a tad unstable while this is ongoing.

Other than that, it is a bit of a miracle that melonDS has been going for so long, and that after so long we're still around and coming up with ambitious plans. I've had several other personal projects, and none of them made it far past the one-year mark (or I only still work on them in a much more sporadic manner, like blargSNES). So, long live melonDS.

On my side, I quit my antidepressant in September, which went much more smoothly than I imagined. I've had a few bouts of depression since then, but nothing really bad, it's completely incomparable to what it was last year, and it's progressively getting better. I'm hopeful.

I tried Ritalin again, but it seemed to make me depressed after a while, so that's a bummer. I have a few ideas for other possibilities, but in the meantime I'm back to being unmedicated. Since this is how it's been for most of my life, I have coping strategies already, but the low energy part of it kinda sucks.

May 2024 be filled with success.
The RTC rework is done

melonDS has got a fun little dialog for changing the date and time now.

Basically what it does is show you the current date and time of the emulated DS. You can change it to any date and time, or you can reset it back to your computer's date and time.

What you set is saved as an offset in seconds from your computer's time. Every time you launch a game, the computer's time is used as a reference to calculate the emulated DS's time, and then melonDS does its own time counting from this point.

This also means that, unlike the previous behavior, if melonDS runs too slow or too fast, it will affect the passage of time for the emulated game from your perspective. The point is to keep melonDS's time counting accurate from the perspective of the game.

This was also the occasion to rework the RTC emulation itself, because it was quite lacking.

For example, when returning the current time, it would simply return the current hour from 0 to 23, ignoring the AM/PM flag that is also encoded in the hour register. It gets a bit weird, because the way this register works depends on the 12/24-hour setting in status register 1. In 24-hour mode, the register goes from 0 to 23, and the AM/PM flag is automatically based on that. In 12-hour mode, the register goes from 0 to 11, and the AM/PM flag needs to be set properly for things to function.

I was also able to add support for writing to the date/time registers. This means that for example, you can boot the DS firmware and change the time from there, and melonDS's date and time setting will reflect that. Perhaps not very useful, but a nice touch regardless.

... read more
RTC and ambitious plans
Two main things this post will talk about.

The RTC, aka Real-Time Clock. The DS uses a RTC chip to keep track of the current date and time. melonDS has had some RTC emulation since the early days, because it was a requirement to get the firmware to boot, but since then, that RTC emulation has been pretty much barebones. Basically, all it does is return the current system time from the host. While it's good enough for the most basic purposes, it comes with a number of downsides.

For example, we've had several requests from end users about changing the time inside melonDS. Currently, the only way to do that is to change your computer's time. melonDS offers no UI for setting its own time. It is possible to boot into the firmware and use the settings menu there, but melonDS ignores writes to the RTC date/time registers, so it just reverts back to the host system time. Less than ideal.

This is also a problem for netplay. The basic idea behind netplay is that all players run the same emulation, and inputs are synced across them. For this to work, you need to ensure that for all players the emulation starts from the exact same state, and that the inputs are the exact same for everybody. Since games use the RTC to initialize their random number generators, all sides need to start from the exact same time, or they will desync. So the basic, "let's just return the system time" RTC won't do here.

Then there's also the fact that this RTC emulation we have is incomplete. The RTC does more than just keep the current time: it features several 'alarm' settings that can trigger interrupts, for example. libnds uses that feature to do its time counting, so if you run any libnds homebrew in melonDS, it will seem stuck at the same time.

The DS firmware also has an alarm clock feature. While I doubt anybody out there is going to use melonDS as their alarm clock, emulating it would be a nice touch.

Regardless, I started working on the RTC yesterday. The first part is to have the RTC in melonDS do its own time counting. The RTC in the DS is likely controlled by a 32768 Hz clock, as is typical for these things, so I did something similar in melonDS, as it will be a requirement for emulating the alarm interrupt features.

I used the system event scheduler in melonDS for this purpose. It is technically inaccurate, because the scheduler runs on the DS system clock (33.51 MHz), but it provides a reliable way to keep the emulated RTC in sync with the rest of the system. I had to get a bit fancy to correct for the inaccuracy from using the system clock as a base, but nothing bad.

From there, I laid down the basic idea of a clock. Have a bunch of registers for the current date and time, count one second every 32768 RTC ticks, count one minute whenever the second register reaches 60, count one hour whenever the minute register reaches 60, etc... You get the idea. As there's currently no way to tell the melonDS core which time to use on startup, it starts at 01/01/2000 00:00:00, but it does count up properly so far.

... read more