There is support in naken_asm for all processors inside the Playstation 2. Both vector units and the R5900 core, including the SIMD instructions, are support. For examples how to write code:
- https://www.mikekohn.net/software/playstation2.php
- https://www.mikekohn.net/micro/playstation2_java.php
For more documentation on the R5900 see the MIPS page.