Switch News: Mesosphere, an open-source re-implementation of the Switch OS’ kernel, gets to the point of booting most games – Will help greatly with Switch emulation!

In April, the roadmap for the Atmosphere CFW for Switch consoles received an overhaul and one of the notheworthy things in the pipeline was mesosphere which is an open-source reimplementation of Horizon OS’ kernel. Now, a good deal of progress has been made and this reimplementation can already run most commercial games with it being ~90% finished!

What is mesosphere? At what stage is it?

With mesosphere, SciresM has been able to boot various commercial games including Puyo Puyo Tetris! (Tweet)

As mentioned in the introduction, mesosphere is a re-implementation of Horizon OS’ kernel which is the operating system that’s bundled with the Nintendo Switch. Its development was brought about by the fact that the Atmosphere CFW, of which SciresM is the primary developer, aims to re-implement components of Horizon OS rather than simply applying patches to them which comes with various benefits including a better understanding of what’s going on although this approach is obviously no walk in the park. Work on it has been going on for about 6 months in a semi-active fashion and according to Atmosphere’s roadmap, it’s slated for a Mid-to-Late 2020 release but SciresM has decided to share with the community the progress he has made thus far which is truly significant.

In a Reddit thread shared late last week, SciresM explains his love for Horizon OS and then goes on to say that Atmosphere was initially a project to re-implement the 3DS’ ARM9 kernel but that was eventually scrapped since the project was “too ambitious” for him. However, SciresM has now accrued enough experience making it possible for him to succeed in creating an open-source re-implementation of the Switch’s kernel and in its current state, mesosphere is around ~90% finished & can boot most commercial games with lots of progress being made ever since the kernel became mature enough to get to the boot logo! Among the titles that SciresM has been successful in booting, one can find Animal Crossing, Fire Emblem Three Houses and the Pokémon titles together with Puyo Puyo Tetris.

How can it help emulation?

Other than simply being a feat, mesosphere is said to be very beneficial to those developing Switch emulators for PC since it eliminates the need to reverse engineer the console’s kernel! (Image from Ryujinx’s website)

After describing mesosphere’s advanced state, SciresM then went on to discuss the effects that his re-implemented kernel will have on the emulation scene. He explains that thanks to mesosphere, those developing Switch emulators will have their life made much easier since they no longer have to reverse engineer kernel behaviour when writing HLE code as mesosphere’s source code can be referenced to check out how stuff works. This is almost guaranteed to be correct as the code is being tested on Switch consoles and will see more testing going forward.

Furthermore, SciresM states that the research he performed before embarking on the mesosphere project has been beneficial to Yuzu and Ryujinx which are the two big players when it comes to Switch emulation while also wishing that his work will enable major HLE improvements in the foreseeable future.


In a tweet, SciresM also stated that Atmosphere-3DS will eventually be picked up again meaning that we’ll eventually be seeing an open-source re-implementation of the 3DS’ kernel as well which will undoubtedly help with emulation! For the latest news on Atmosphere, mesosphere and other stuff that SciresM is working for, you should follow his Twitter account linked below. Code relating to mesosphere has also been shared in two GitHub branches which can be accessed from the links below.

SciresM Twitter Account: https://twitter.com/SciresM

mesosphere/kernel Branch in Atmosphere’s Repository: https://github.com/Atmosphere-NX/Atmosphere/tree/mesosphere-dev/mesosphere/kernel

libraries/libmesosphere in Atmosphere’s Repository: https://github.com/Atmosphere-NX/Atmosphere/tree/mesosphere-dev/libraries/libmesosphere