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Cafe OS is the operating system running on the PowerPC in Wii U mode. It consists of the Cafe OS kernel, the executable loader, and system libraries. Unlike on the Wii, where games ran with full hardware access, Wii U applications run under the supervision of the kernel, isolating them from each other. All applications are [[RPL|modified ELFs]], as are the libraries themselves, and applications dynamically link with them to gain access to OS services. Cafe OS also contains a few system processes, like the home menu and error handler.

Cafe OS is the operating system running on the PowerPC in Wii U mode. It consists of the Cafe OS kernel, the executable loader, and system libraries. Unlike on the Wii, where games ran with full hardware access, Wii U applications run under the supervision of the kernel, isolating them from each other. All applications are [[RPL|modified ELFs]], as are the libraries themselves, and applications dynamically link with them to gain access to OS services. Cafe OS also contains a few system processes, like the home menu and error handler.

==Architecture==

== Architecture ==

===Kernel===

=== Kernel ===

 

The kernel runs in supervisor mode on the PowerPC, and performs the basic tasks of a microkernel. It is responsible for process isolation, memory management, and interrupt dispatching, as well as communication with [[IOSU]]. Cafe OS applications run as user mode processes, with separate address spaces and W^X memory protection. The kernel provides basic [[Cafe_OS_Syscalls|syscalls]] for running processes.

The kernel runs in supervisor mode on the PowerPC, and performs the basic tasks of a microkernel. It is responsible for process isolation, memory management, and interrupt dispatching, as well as communication with [[IOSU]]. Cafe OS applications run as user mode processes, with separate address spaces and W^X memory protection. The kernel provides basic [[Cafe_OS_Syscalls|syscalls]] for running processes.

===Processes===

=== Processes ===

A process in Cafe OS represents a single running application, with its own code, memory, and permissions. Cafe OS only executes the code of a single process at a time, but it can hold the data of multiple processes in memory simultaneously, and switch between them. Rather than allowing arbitrary process creation, there is RAM reserved for a single foreground app, a single background app, and various other special processes. Each running process is assigned a unique identifier called a RAMPID:

A process in Cafe OS represents a single running application, with its own code, memory, and permissions. Cafe OS only executes the code of a single process at a time, but it can hold the data of multiple processes in memory simultaneously, and switch between them. Rather than allowing arbitrary process creation, there is RAM reserved for a single foreground app, a single background app, and various other special processes. Each running process is assigned a unique identifier called a RAMPID:

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===Loader===

=== Loader ===

{{Main|Loader}}

{{Main|Loader}}

The loader is responsible for loading RPL formatted libraries and executables into memory. It is a standard ELF executable named loader.elf. It includes a statically linked copy of zlib, probably for decompressing sections of RPL files.

The loader is responsible for loading RPL formatted libraries and executables into memory. It is a standard ELF executable named loader.elf. It includes a statically linked copy of zlib, probably for decompressing sections of RPL files.

===Libraries===

=== Libraries ===

Cafe OS applications dynamically link with system libraries to get access to OS services. These OS services include memory management, graphics, audio, and controller input. All libraries are [[RPL|RPL files]], a modification of the standard ELF format with compressed sections and more Windows-like dynamic linking. The main system libraries are listed below, with some having their own pages of documentation:

Cafe OS applications dynamically link with system libraries to get access to OS services. These OS services include memory management, graphics, audio, and controller input. All libraries are [[RPL|RPL files]], a modification of the standard ELF format with compressed sections and more Windows-like dynamic linking. The main system libraries are listed below, with some having their own pages of documentation:

*[[avm.rpl]] - Audio/Video Manager

*[[avm.rpl]] - Audio/Video Manager

*[https://github.com/madler/zlib/tree/9712272c78b9d9c93746d9c8e156a3728c65ca72 zlib125.rpl] - ZLIB 1.2.5, functions match official library

*[https://github.com/madler/zlib/tree/9712272c78b9d9c93746d9c8e156a3728c65ca72 zlib125.rpl] - ZLIB 1.2.5, functions match official library

==Virtual Memory Map==

== Virtual Memory Map ==

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