DSLinux running on a DS Lite using the M3 DS Simply and M3 DS Adapter
|Written in||C++, C|
|Source model||Open source|
|Kernel type||Modified μClinux|
|License||GNU GPLv2 or later|
DSLinux runs a modified μClinux kernel. It is based on uCLinux 2.6.14 (Linux-2.6.14-hsc0). It only runs in textmode and nano-x which is displayed using a custom framebuffer console driver. A keyboard is displayed on the touchscreen of the Nintendo DS to allow user input.
ncurses, libpcap, SDL along with many other libraries have been ported, so DSLinux is in theory capable of running almost any application that has an ncurses-based or framebuffer based user interface. It also runs basic shell applications provided by BusyBox and GNU Coreutils has also been ported. The C-library is uClibc.
DSLinux has no package management facilities. Instead, DSLinux builds are distributed as a single tar archive.
With the exception of the microphone (it works, but the driver is incomplete), all hardware inside the Nintendo DS, including the wireless is supported by DSLinux. The Nintendo DS firmware can be read from /dev/firmware, but write support is left out for safety reasons.
DSLinux supports storing files on a variety of add-on hardware devices, none of which are officially endorsed by Nintendo. DSLinux can store files in SRAM memory found in GBA Flash Carts and CompactFlash and SD cards, which can be used with any of the following adaptors: GBAMP, M3, or SuperCard. Newer versions have included DLDI support, allowing for a much wider range of compatibility.
The Nintendo DS does not have a memory management unit (MMU), and has only 4 MB (The later versions of the DSi and DSi XL have 16mb) of RAM but all units are limited by the very old ARM 7 and ARM 9 processor duo that the system runs. Both kernel and userspace XIP and SLOB memory allocation were the first techniques used to increase the amount of available RAM a little. Later, support for the internal RAM present on some add-on hardware devices, such as the SuperCard or M3, has been added, offering up to an extra 32MB of memory. Adding support for external RAM was not trivial, as the GBA slot bus only supports 16-bit writes. If only 8 bits are sent over the bus, the result ending up in memory is garbage. A DSLinux developer called Amadeus found a workaround for this, which involved replacing "strb" (store byte) ARM assembly instructions with "swpb" (swap byte) instructions. The swpb instruction first reads from the requested address, populating the data cache, then the 8-bit write is performed into the cache. Later, when the cache line is evicted, 16-bit writes are used, thus eliminating all 8-bit writes over the bus. Amadeus modified the GCC code generator for ARM so that all applications compiled for DSLinux now use swpb instead of strb instructions. Assembly code in the Linux kernel had to be adapted manually.