Dreamcast low-level dev.

The Dreamcast can be a challenging target for codegolfing, the SH-4 CPU is a traditional RISC to the core with 16-bit instruction size, this is good for codegolfing but being RISC and without the "hacks" of similar RISC CPU such as ARM (barrel shifter) there is constraints such as :

• MOV only supports an 8-bit immediate; loading constants may pass by a load operation or tricks
  
• you cannot shift by arbitrary constant amount
• delay slot
  
• available addressing modes may be annoying although not so horrible for RISC
  

There is some 256b and 128b for Dreamcast but they don't run anymore on the emulators i tried, to run them you may have to use official BIOS file and change VIDEO_RAM (and also VIDEO_BASE) constant to 0xa5200000 instead of 0xa5000000 then assemble. (see setup below)

The reason is that the Dreamcast BootROM sets video framebuffer base to 0xa5200000 (a 2MB offset from base VRAM), the 2MB below is reserved for a copy of the BootROM to pass bootup checks, it is likely that this wasn't emulated at the time of these intros or that the framebuffer base was already changed to 0xa5000000 due to the method by which they ran. Modifying the framebuffer base to be 0xa5000000 after boot is expected so that all the VRAM is available without fragmentation, this can be safely ignored for code golfing purposes though.

It is not a perfect solution anyway to run these intros because they will run in a tiny area of the screen after this fix, this might be due to the intro being made for a different video mode... didn't look yet but what i know is that after boot the display mode is 640*480 ARGB8888, this might depend on BIOS / video connection type though (cable type in Redream) which was set to RGB for my test.

The alternative to run the original code of these intros is to setup the framebuffer start address and a video mode, this is much bigger obviously, it can be done by looking at dreamhal videos mode setup.

• dreamhal hardware abstraction library is a good quick starting resource (C code)
  
• SH4 manual and hardware documentation can be found here
• memory map
  
• Dreamcast Dev/Box manual can be also useful
• Raymond Chen articles on the SuperH-3 is incredibly useful as a starting point (and apply to SH-4), giving many hints and tricks
• making games for the Dreamcast using standard GNU tools
• Dreamcast documentation and source code for bare metal coding
  

Here is a guide to setup a Dreamcast development environment, note that i was only interested in running SH4 assembly code for raw graphics stuff so i didn't test anything else :

Emulators