Reality Signal Processor/Interface
The RSP interface is accessed by VR4300 via memory mapped registers at the physical address 0x040x xxxx.
DMEM and IMEM
Both RSP memory banks are fully memory mapped into the VR4300 address space, as follows:
| Address range | Memory | |
|---|---|---|
| 0x04000000 | 0x04000FFF | RSP DMEM |
| 0x04001000 | 0x04001FFF | RSP IMEM |
Access must be performed using 32-bit reads and writes. TODO: document exact behavior on different access sizes.
Since the memory is single-port, it can only be accessed by either the VR4300 or the RSP itself at the same time (including its internal DMA engine). Notice that there is no bus arbiter: an access happening at the same time by both processors will cause problems: typically what happens is that VR4300 wins the race, so the RSP write is lost, or the RSP read returns the same data read by the VR4300 (even if the address was different). Also, if a DMA was in progress, the address of the memory access performed by VR4300 becomes the current address of the DMA transfer, corrupting it. So, in general, VR4300 should access DMEM/IMEM only when RSP is halted.
RSP Internal Registers
The internal RSP registers are memory mapped into the VR4300 physical address space starting from 0x0404 0000. Normally, accessed are performed through the virtual uncached segment, so at 0xA404 0000.
The exact same physical registers are also exposed as COP0 registers to RSP itself, and can thus be accessed using the MTC0 / MFC0 opcodes.
SP_MEM_ADDR 0x0404 0000
| ||||||||
|---|---|---|---|---|---|---|---|---|
| 31:24 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 |
| — | — | — | — | — | — | — | — | |
| 23:16 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 |
| — | — | — | — | — | — | — | — | |
| 15:8 | U-0 | U-0 | U-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 |
| MEM_ADDR[11:8] | ||||||||
| 7:0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 |
| MEM_ADDR[7:0] | ||||||||
| bit 31-13 | Undefined: Initialized to 0
|
| bit 12 | MEM_BANK[12]: 11-0 |
| bit MEM_ADDR[11:0] | DMEM or IMEM address used in SP DMAs: DMEM, 1=IMEM. |
SP_DRAM_ADDR 0x0404 0004
| ||||||||
|---|---|---|---|---|---|---|---|---|
| 31:24 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 | U-0 |
| — | — | — | — | — | — | — | — | |
| 23:16 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 |
| DRAM_ADDR[23:16] | ||||||||
| 15:8 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 |
| DRAM_ADDR[15:8] | ||||||||
| 7:0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 | RW-0 |
| DRAM_ADDR[7:0] | ||||||||
| bit 31-24 | Undefined: Initialized to 0
|
| bit 23-0 | DRAM_ADDR[23:0]: RDRAM address used in SP DMAs |