Vector Units

This section is in beta. See the note on the cheat sheet.

The EE has two attached Vector Units, VU0 and VU1. They are small processors for vector and matrix arithmetic.

VU0 and VU1

VU0 sits close to the EE and runs in one of two modes: as a tightly coupled coprocessor that the EE issues instructions to like an extension of its own pipeline, or running its own microprogram. It is commonly used for per-vertex and per-object math such as skinning and lighting terms, interleaved with regular EE code.

VU1 is more independent. It typically runs its own microprogram continuously, fed vertex and matrix data over DMA_CHANNEL_VIF1. Its usual job is described in Graphics Synthesizer: it transforms vertices and builds the GIF packet for the GS, so the EE can move on to the next frame's logic while VU1 works.

VU programs

math3d (core) is EE-side vector and matrix math, not VU microcode. VU programs in this SDK are:

• Hand-written VU assembly or VCL (a VU-targeting compiler) source, compiled separately and embedded or loaded like any other binary.
• Pre-built microprograms bundled in a higher-level library. gsKit and ps2gl each include a VU1 microprogram that transforms vertices and builds packets.

See also

• Graphics Synthesizer
• DMA - VIF0 and VIF1 carry data to VU0 and VU1