Memory map

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Revision as of 02:27, 29 March 2022 by Bigbass (talk | contribs) (Removed duplicate link to RDRAM registers)
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The Memory Management Unit (MMU) in the CPU utilizes a large virtual memory space to map to various physical addresses in different ways. All memory accesses made by the CPU, whether instruction fetches or load/store instructions, use virtual addresses. The MMU uses five virtual memory segments to decide how the addresses will be mapped to the physical memory space.

Internally, all addresses are 64-bits wide. However, when in 32-bit addressing mode, the upper 32 bits are sign-extended.

Virtual Memory Map

Address Range Name Description
0x00000000 0x7FFFFFFF KUSEG User segment, TLB mapped
0x80000000 0x9FFFFFFF KSEG0 Kernel segment 0, directly mapped, cached
0xA0000000 0xBFFFFFFF KSEG1 Kernel segment 1, directly mapped, uncached
0xC0000000 0xDFFFFFFF KSSEG Kernel supervisor segment, TLB mapped
0xE0000000 0xFFFFFFFF KSEG3 Kernel segment 3, TLB mapped

For the directly mapped segments KSEG0 and KSEG1, addresses are directly translated to physical addresses by subtracting by the base address of the respective segment. Thus they can only map to the physical address range 0x00000000 - 0x1FFFFFFF.

Refer to the Translation lookaside buffer article and the TLB mapping usage guide for more information about TLB mapped segments.

Physical Memory Map

Address Range Name Description
0x00000000 0x003FFFFF RDRAM RDRAM located on motherboard
0x00400000 0x007FFFFF RDRAM RDRAM from Expansion Pak (if present)
0x00800000 0x03EFFFFF Reserved Unknown usage
0x03F00000 0x03FFFFFF RDRAM Registers RDRAM configuration registers
0x04000000 0x04000FFF RSP DMEM RSP Data Memory
0x04001000 0x04001FFF RSP IMEM RSP Instruction Memory
0x04002000 0x0403FFFF Unknown Unknown
0x04040000 0x040FFFFF RSP Registers RSP DMAs, status, semaphore, program counter, IMEM BIST status
0x04100000 0x041FFFFF RDP Command Registers RDP DMAs, clock counters for: clock, buffer busy, pipe busy, and TMEM load
0x04200000 0x042FFFFF RDP Span Registers TMEM BIST status, DP Span testing mode
0x04300000 0x043FFFFF MIPS Interface (MI) Init mode, ebus test mode, RDRAM register mode, hardware version, interrupt status, interrupt masks
0x04400000 0x044FFFFF Video Interface (VI) Video control registers
0x04500000 0x045FFFFF Audio Interface (AI) Audio DMAs, Audio DAC clock divider
0x04600000 0x046FFFFF Peripheral Interface (PI) Cartridge port DMAs, status, Domain 1 and 2 speed/latency/page-size controls
0x04700000 0x047FFFFF RDRAM Interface (RI) Operating mode, current load, refresh/select config, latency, error and bank status
0x04800000 0x048FFFFF Serial Interface (SI) SI DMAs, PIF status
0x04900000 0x04FFFFFF Unused Unused
0x05000000 0x05FFFFFF Cartridge Domain 2 Address 1 N64DD control registers (if present)
0x06000000 0x07FFFFFF Cartridge Domain 1 Address 1 N64DD IPL ROM (if present)
0x08000000 0x0FFFFFFF Cartridge Domain 2 Address 2 Cartridge SRAM (if present)
0x10000000 0x1FBFFFFF Cartridge Domain 1 Address 2 Cartridge ROM
0x1FC00000 0x1FC007BF PIF ROM (IPL1/2) Executed on boot
0x1FC007C0 0x1FC007FF PIF RAM Controller and EEPROM communication, and during IPL1/2 is used to read startup data from the PIF
0x1FC00800 0x1FCFFFFF Reserved Unknown usage
0x1FD00000 0x7FFFFFFF Cartridge Domain 1 Address 3 Mapped to same address range on physical cartridge port
0x80000000 0xFFFFFFFF External SysAD device bus Unknown usage (Unconfirmed: possibly used by processors, cache, and/or RAM for communication)

Cartridge Domains 1 and 2 are mapped one-to-one on the cartridge/bottom port. It is not known at this time what Domain 1 Address 3 was used for, if at all, but flash carts may have some use for that address range.