The Smallest .nds, ever

Have you ever wondered what exactly is inside a Nintendo DS ROM file, and why the simple DS demos are so much larger than their GBA equivalents? Some people have, and this page documents their exploits.

Introduction
It started innocently enough. I was looking for a small ROM which would be used to test the framebuffer display mode of DSemu, a Nintendo DS emulator. LiraNuna agreed to put a small C demo together, to fill the 'main' screen with red, demonstrating the framebuffer's use. When compiled and spliced up, the .nds ended up at around 7.5KB.

That, LiraNuna thought, was a bit large for something that did so little as his demo evidently did. Stepping through with DSemu's debugger, I noticed a whole lot of code being run which wasn't strictly required: setting up cache parameters and the stack, clearing out regions of memory, and such like. Referred to as the crt0, this code is inserted into every project, to safeguard the execution environment.

Furthermore, there was the standard ARM7 code also inserted into the .nds file, which does such things as set up the touchscreen. All this, we thought, was a bit over-the-top for a demo that was literally doing almost nothing. So, the cut-down began.

http://dsemu.org/The_Smallest_NDS.html