Reality Display Processor
The Reality Display Processor, or RDP, is the portion of the RCP responsible for graphics tasks such as Z-buffering, texturing, blending, anti-aliasing, etc. It contains 4KB of texture memory (TMEM,) and is sent commands called "primitives".
RDP interface
The RDP interface is made of several memory-mapped registers that allows the VR4300 and RSP to control the RDP. Both VR4300 and RSP are in fact able to control RDP execution by accessing the interface: VR4300 through memory mapped registers, while RSP through its COP0.
RDP commands
The RDP processes a fixed-function command list comprised of primitive rendering, attribute setting, texture loading, and synchronization commands. Most commands are 64-bit words, though some are bigger. Command lists can be sent to RDP via DMA, either from RDRAM or DMEM.
RDP pipeline
The RDP is a pipelined processor with configurable pipeline modes. It is up to the user to select the appropriate operating mode and provide adequate synchronization in submitted command lists.