Cafe OS

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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 each game provided its own copy of Revolution OS with no isolation between libraries, Wii U applications run under the supervision of a common PowerPC kernel, isolating them from each other. All applications are 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. IPC to the IOP (IOSU) is managed by the Cafe OS Kernel and an IPC driver.

Pages

Kernel

Main article: Cafe OS/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.

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:

RAMPID Description IOS Name
0 Cafe OS COS-KERNEL
1 root.rpx COS-ROOT
2 ??? COS-02
3 ??? COS-03
4 Background app COS-OVERLAY
5 HOME Menu COS-HBM
6 Error display COS-ERROR
7 Foreground app COS-MASTER

In addition to RAMPID, Cafe OS processes have another type of process ID called a fixed process ID (PFID). Rather than representing which part of memory a process occupies, PFID actually specifies which specific app/task is running (browser, game, eShop, etc.). Cafe OS maps PFIDs to the RAMPID that they occupy when running (for example, a game is RAMPID 7 due to running in the foreground):

PFID Description RAMPID
0 Cafe OS kernel 0
1 root.rpx 1
2 Wii U Menu 7
3 Nintendo TVii ???
4 E-Manual ???
5 HOME Menu 5
6 Error Display 6
7 Miiverse Post App ???
8 Internet Browser 4
9 Miiverse ???
10 Nintendo eShop ???
11 COS-FLV ???
12 Download Manager ???
13 COS-RSVD-13 ???
14 COS-RSVD-14 ???
15 Game 7
16 AOC Overlay App ???
17 amiibo Settings ???
31 Test Overlay ???

Loader

Main article: 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.

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 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:

Virtual Memory Map

Virtual address start Virtual address size Physical address start Flags Description
0x1000000 0x800000 0x32000000 0x2CE08002 Loader and system libraries
0x1800000 0x20000 0 0x28101200 This is the codegen/JIT memory area, only available under processes which have it enabled under cos.xml (the size comes from cos.xml too)
0x2000000 (variable) 0xE000000 (variable) 0x72000000 or 0xB2000000 (variable) 0x2CF09400 App executable and libraries (start varies, but end is always 0x10000000)
0x10000000 0x52000000 or 0x92000000 (variable) 0x20000000 (variable) 0x28305800 Application/library data area (may be smaller)
0xA0000000 0x40000000 0 0x2000 Overlay of application memory (used by loader?)
0xE0000000 0x4000000 0x14000000 0x28204004 Some sort of hardware communication area
0xE8000000 0x2000000 0xD0000000 0x78200004
0xEFE00000 0x80000 0x1B900000 0x28109010 Loader data area (only mapped when running loader)
0xF4000000 0x2000000 0 0x28204004 MEM1
0xF6000000 0x800000 0x1B000000 0x3CA08002 Loader chunk buffer
0xF8000000 0x3000000 0x18000000 0x2CA08002 Read-only shared data (system fonts mostly)
0xFB000000 0x800000 0x1C800000 0x28200002
0xFC000000 0xC0000 0xC000000 0x70100022 Processor Interface
0xFC0C0000 0x120000 0xC0C0000 0x70100022
0xFC1E0000 0x20000 0xC1E0000 0x78100024 VI
0xFC200000 0x80000 0xC200000 0x78100024 GFXSP
0xFC280000 0x20000 0xC280000 0x78100024 DSP
0xFC2A0000 0x20000 0xC2A0000 0x78100023 Write Gather Pipe
0xFC300000 0x20000 0xC300000 0x78100024
0xFC320000 0xE0000 0xC320000 0x70100022 Espresso eFuses
0xFD000000 0x400000 0xD000000 0x70100022 Latte Registers
0xFE000000 0x800000 0x1C000000 0x20200002
0xFF200000 0x80000 0x1B800000 0x20100040 Kernel heap
0xFF280000 0x80000 0x1B880000 0x20100040
0xFFC00000 0x20000 0xFFC00000 0x8100004 Codegen area used with OSCodegenCopy
0xFFC40000 0x20000 0xFFC40000 0x8100004 Codegen area used with OSCodegenCopy
0xFFC80000 0x20000 0xFFC80000 0x810000C Codegen area used with OSCodegenCopy
0xFFCE0000 0x20000 0 0x50100004
0xFFE00000 0x20000 0xFFE00000 0x20100040 Kernel ancast image
0xFFE40000 0x20000 0xFFE40000 0x20100040
0xFFE80000 0x60000 0xFFE80000 0x20100040
0xFFEE0000 0x20000 0xFFEE0000 0x20100040
0xFFF00000 0x20000 0xFFF00000 0x20100040
0xFFF60000 0x20000 0xFFE20000 0x20100080
0xFFF80000 0x20000 0xFFE60000 0x2C100040
0xFFFA0000 0x20000 0xFFE60000 0x20100080
0xFFFC0000 0x20000 0x1BFE0000 0x24100002
0xFFFE0000 0x20000 0x1BF80000 0x28100102 Per-thread data (e.g. pointer to thread descriptor and thread queue) at 0xFFFFFFE0 - 0xFFFFFFFC.
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