SunPlus released sources for the C compiler. It doesn't include the assembler and is based on GCC 2.95 so quite hard to compile: https://github.com/vsmile-dev/unsp-gcc
Work in progress port of vbcc: http://pulkomandy.tk/gerrit/plugins/gitiles/vbcc/+/refs/heads/unsp
The lack of vasm or another assembler with object file format and linker makes this hard to use. For now, the compiler generates output compatible with naken_asm, then all the output asm files need to be concatenated and fed directly into the assembler. And there isn't really support for sections or any fancy stuff like that, so getting the variables in RAM and the code in ROM is a bit messy.
Also, the code generation is completely unoptimized currently. Adding support for at least pre and post incrementation decrementation would be a great help in generating simpler code.
XASM is the original assembler provided by the µ'nSP IDE
naken_asm has support for µ'nSP and provides a standard include file for SPG200 registers.
This early homebrew experiment took an interesting approach of not using an assembler at all.
- https://github.com/gameblabla/png2vsmile - PNG converter to VSmile background bitmap format