Dmem; Addressing; Explicitly Managed Resource - Nintendo Ultra64 Programmer's Manual

RSP Architecture

DMEM

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The RSP has 4K bytes of data memory (DMEM).

Addressing

Since DMEM is 4K bytes, only the lowest 12-bits of addresses are used to
address DMEM. Other address bits are ignored.

Explicitly Managed Resource

DMEM must be managed by the RSP program. All RSP loads/stores can
only access DMEM; data must first be transferred between DMEM and
external DRAM using a DMA operation (or programmed IO write from the
CPU).