MIPS Assembly programming for the Playstation 1 (PS1/PSX)

The Playstation was Sony's first home console, While inferior in some ways to the more powerful N64, the Playstations huge storage capability, combined with an impressive game library saw the Playstation become the most popular console of the period, catapulting the playstation to the top of the console market.

Cpu	33.87 mhz R3000 (MIPS I)
Ram	2MB
Video	1MB VRAM
Resolution	256x224 / 320x240 / 640x480

Documentation

Nocash PSXSPX Playstation Specifications

Memory Map

KUSEG	KSEG0 (Cached)	KSEG1 (Uncached)	KSEG2 (IO Ports)	Size	Purpose
0x00000000	0x80000000	0xA0000000	--	2048K	Main RAM (first 64K reserved for BIOS)
0x1F000000	0x9F000000	0xBF000000	--	8192K	Expansion Region 1 (ROM/RAM)
0x1F800000	0x9F800000	--	--	1K	Scratchpad (D-Cache used as Fast RAM)
0x1F801000	0x9F801000	0xBF801000	--	8K	I/O Ports
0x1F802000	0x9F802000	0xBF802000	--	8K	Expansion Region 2 (I/O Ports)
0x1FA00000	0x9FA00000	0xBFA00000	--	2048K	Expansion Region 3 (whatever purpose)
0x1FC00000	0x9FC00000	0xBFC00000	--	512K	BIOS ROM (Kernel) (4096K max)
--	--	--	0xFFFE0000	0.5K	I/O Ports (Cache Control)

Gpu Commands

Written to port 0x1F801810

Function	Byte	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Clear Cache	0	0x01								0
Function	Byte	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Set Screen Width	0	0x06								End X												Start X
Function	Byte	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Send image to Framebuffer	0	0xA0
CPU to VRAM	1	Y																X
	2	H																W
	3	Pixel 2																Pixel 1
	..	..																...
	n	Pixel n*2+1																Pixel n*2
Function	Byte	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Fill Area	0	0x02								Color
	1	Y																X
	2	H																W
Function	Byte	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Copy Rectangle	0	0x80
VRAM to VRAM	1	SY																SX
	2	DY																DX
	3	H																W
Function	Byte	31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Get image from Framebuffer	0	0xC0
VRAM to CPU	1	Y																X
	2	H																W
read from GPUREAD port	3	Pixel 2																Pixel 1
	..	..																...
	n	Pixel n*2+1																Pixel n*2

Screen Memory

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

Joypad Bits

We want to start the joypad reading routine.

First we set up a valid stack pointer, Next we're going to call the bios function at address 0x000000B0

The command is stored in register T1, A1,A2,A3 and A4 contain the parameters

We point A0 and A2 to 'Joydata'... once we perform these two bios calls, the JoyData memory will automatically be updated with the data from the joypad

The format of the bits in 'JoyData are shown below:

	Bits
Byte	7	6	5	4	3	2	1	0
0	N/A
1	0x41 �A�
2	0x5A �Z�
3	LEFT	DOWN	RGHT	UP	START	1	1	SELECT
4	SQUARE	X	O	TRIANGL	R1	L1	R2	L2

Endian

The N64 is BIG ENDIAN
the PSX is LITTLE ENDIAN