MIPS Assembly programming for the N64

The N64 was Nintendo's first steps into 3D... Built from the technology from the SGI workstations, the N64 gave home users some of the first 3D graphics. While limited compared to modern systems, the N64 was revolutionary for it's day, and gives us an capable system for learning MIPS!

Cpu 93.75mh NEC VR4300 MIPS III Ram 4MB Rambus RDRAM (8mb upgradable) Video SGI RCP  (Reality Co-Processor) Resolution 320x240 / 640x480

Memory Map

Screen Memory

Each pixel is represented by one BIG ENDIAN word, in the format %RRRRRGGGGGBBBBBB-

Endian

The N64 is BIG ENDIAN
the PSX is LITTLE ENDIAN

Reading the joystick

The N64 controllers are connected via the so called 'PIF' chip (Peripheral Interface?) The base of the PIF registers is at address 0xBFC007C0 To initialize things we first write 0x8 to the status register at 0xBFC007FC
We're going to use the serial interface (SI)  to send data to the PIF, This is basically a DMA copy, which sends a block of data. We need to prepare a 96 byte block of data to send to the PIF to initialize things. We also define 8 bytes to get back the results when we do a read!
OK we need to use the SI to Send the INIT code to the PIF The SI registers are at 0xA4800000+ We need to calculate our source address (PIF_Init) - but we need the true 'hardware address' we can get this by ANDing with 0x1FFFFFFF We send the source address to 0xA4800000 (SI_DRAM_ADDR_REG) We want to transfer to the PIF ram at 0xBFC007C0 (PIF_RAM_START) - we also AND this with 0x1FFFFFFF We write the destination to the write register at 0xA4800010 (SI_PIF_ADDR_WR64B_REG) - this write also starts the transfer
OK Let's actually get the keypresses from the joypads! This time we use the SI to READ from the PIF. We need to calculate our destination address (PIF_JoyState) - but we need the true 'hardware address' we can get this by ANDing with 0x1FFFFFFF We send the destination address to 0xA4800000 (SI_DRAM_ADDR_REG) - this is the same as the address for writing This time we want to transfer FROM to the PIF ram at 0xBFC007C0 (PIF_RAM_START) - we also AND this with 0x1FFFFFFF We write the source to the read register 0xA4800004 (SI_PIF_ADDR_RD64B_REG) - this write also starts the transfer
As a test we dump with our memdump sub There are 8 bytes returned, the first 4 are status, the next 4 are directions and buttons in the format: %ABZSUDLR --LRUDLR XXXXXXXX YYYYYYYY AB - A/B Buttons ZLR  - Shoulder buttons / Triggers UDLR - Digital Directions UDLR - C Pad XXXXXXXX YYYYYYYY - Analog stick S - Start