This document is reference for PSXSDK - softawre development toolkit for creating games and applications for Playstation 1 game console. PSXSDK is developed by <nextvolume> since 2008. You can find it here: http://code.google.com/p/psxsdk .
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Important
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PSXSDK has not to be confused with Psy-Q, the official, closed-source Software Development Kit made by Sony much earlier. Both are meant to do the same thing, but they use different tools and techniques to achieve their goal. |
PSXSDK mainly divided in four parts: libraries, compilers, converters and CD-ROM tools.
Programming with plain C, sending data directly into PSX I/O ports is a bit difficult. So the most common tasks are wrapped in functions, which allow you to concentrate on game development.
They are used to create an executable file from a code written in a certain programming language (C in our case). PSXSDK, for example, uses psx-gcc, a modified version of GCC for the MIPS R3000 processor, the one used in PSX. psx-gcc outputs an ELF format file (ELF stands for Executable and Format File).
computers and game systems don’t use the same file formats, so tools are needed to convert them. For example, the aforesaid ELF file should be converted to the PSX executable format using elf2exe. Some of these tools are wag2vag, bmp2tim, mod4psx, psfex, etcetera
this kind of applications are used to create licensed ready-to-burn images of the game. The process consists of creating a .ISO image with mkisofs and, afterwards, mkpsxiso to create the needed .BIN/.CUE files. Lastly, any CD-ROM burner software will allow us to play our game on real hardware.
PSXSDK also includes some more tools for various uses, such as huff (Huffman compressor), systemcnf, exefixup… Some tools will be added later depending on new features added to PSXSDK.
You can meet other people, interested in PSX game development here:
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Irc channel: #unhaut on irc.freenode.net
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Forums: http://unhaut.fav.cc/forums
If you just want to know how much you will be limited in creation of your games, there is a short list of hardware limitations:
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RAM - 2 Mb (in fact 1,5 Mb, because game exe file uses memory too)
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CPU speed - 33 Mhz
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Video Ram - 1 Mb
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possible screen resolutions:
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256 × 224
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320 x 240
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640 x 480
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Audio memory - 512 Kb
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CD-ROM read speed - 300 kB/s
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Memory card capacity - 128 kB
The PSX uses the standard CDROM ISO9660 filesystem without any encryption (ie. you can put an original PSX CDROM into a DOS/Windows computer, and view the content of the files in text or hex editors without problems). But when you creating your own CDROM media, you must remeber, that only 8.3 filenames are supported. That means, 8 letters for filename and 3 letters for file extension.
Maybe one of the most important things when you talk about game programming. VRAM in PSX can be imagines as canvas with size 1024 x 512 pixels. This is two-dimensional address space composed of 16-bit pixels. The top left pixel has the coordinates (0, 0) and the bottom right pixel has the coordinates (1023, 511). Each pixel is made up of three 5-bit data items indicating RGB brightness values, each ranging from 0~31, and a semi-transparency flag. The semi-transparency flag is only valid when the pixel is used as a texture.
Many time per second PSX scan its VRAM and displays it content on your TV screen. You can specify a rectangular area, which must be translated on screen. This area must have size same as one of supported screen resolutions. In this area you can draw lines, polygons, sprites - everything you want user to see during gameplay.
This is display area. You can use just it, but there is a problem - PSX sends picture to TV few times per second, and if you will not finish all drawing untill another sending will be started, the uncomplete picture will be sended on TV. And user will see blinking image.
To prevent it you must use another area - drawing area, where you will draw everything, but which will not be sent on TV. When you end drawing you can switch drawing area to display area. And the display area will become drawing area. And this must be repeated every redrawing cycle. Sounds difficult, but most time you will not think about it, using simple code snippet.
The common state of VRAM is on this diagram.
Just usual CDROM, you must not worry about its speed or buffer size or so. But there is some features, related to this device.
With the above Interleave, files can be played continously at real time - that, unless read-errors do occur. In that case the drive controller would usually perform time-consuming error-correction and/or read-retries. For video/audio streaming the resulting delay would be tendencially more annoying as than processing or skipping the incorrect data. In such cases the drive controller is allowed to ignore read errors; that probably on sectors that have the Real Time (RT) flag set in their subheaders. The controller is probably doing some read-ahead buffering (so, if it has buffered enough data, then it may still perform read retries and/or error correction, as long as it doesn’t affect real time playback). For great sadness streaming now is unsupported in PSXSDK.
We hope, that you had a look into section Overview of Playstation 1 hardware, so principles of programming described below will be clear. The main idea is to initialize PSXSDK libs and launch infinite loop. During this loop you must do game logic, like moving enemies or detecting collisions, read user input, redraw screen.
The best way to got into soething is to see example how to do it, right?
#include <psx.h>
#include <stdio.h>
unsigned int prim_list[0x4000];
volatile int display_is_old = 1;
volatile int time_counter = 0;
int dbuf=0;
void prog_vblank_handler() {
display_is_old = 1;
time_counter++;
}
int main() {
/* Basic initialization, you will need it in every game */
PSX_Init();
GsInit();
GsSetList(prim_list);
GsClearMem();
/* Here you set screen resolution of your game and video mode */
GsSetVideoMode(320, 240, VMODE_PAL);
/* you need to load font if you want to use GsPrintFont function */
GsLoadFont(768, 0, 768, 256);
/*
set a function which will be called every time image will be
sent to TV
*/
SetVBlankHandler(prog_vblank_handler);
/* Infinite loop of your game */
while(1) {
/* here we check if image was sent to TV */
/* if sent - we start drawing again */
if(display_is_old) {
/* changing flag of
dbuf=!dbuf;
/* here we switch drawing area and display area */
GsSetDispEnvSimple(0, dbuf ? 0 : 256);
GsSetDrawEnvSimple(0, dbuf ? 256 : 0, 320, 240);
/* clear drawing area */
GsSortCls(0,0,0);
/* print the text on the drawing area */
GsPrintFont(70, 120, "Hello world from PSX");
GsDrawList();
while(GsIsDrawing());
/* set flag to prevent redrawing until drawed picture will be sent on TV */
display_is_old=0;
}
}
return 0;
}After your output something on TV screen, the second question is - how to handle user’s input? The most common device used almost in every PSX game is a gamepad. For now it will be enough.
The main idea here, that you can check state of any gamepad key when you need it. There is no interruption handling or so. Let’s see an example.
#include <psx.h>
#include <stdio.h>
unsigned int prim_list[0x4000];
/* here we will save gamepad state */
unsigned short padbuf;
volatile int display_is_old = 1;
volatile int time_counter = 0;
int dbuf=0;
int hx=0, hy=0;
void prog_vblank_handler() {
display_is_old = 1;
time_counter++;
}
int main() {
PSX_Init();
GsInit();
GsSetList(prim_list);
GsClearMem();
GsSetVideoMode(320, 240, VMODE_PAL);
GsLoadFont(768, 0, 768, 256);
SetVBlankHandler(prog_vblank_handler);
while(1) {
if(display_is_old) {
dbuf=!dbuf;
GsSetDispEnvSimple(0, dbuf ? 0 : 256);
GsSetDrawEnvSimple(0, dbuf ? 256 : 0, 320, 240);
GsSortCls(0,0,0);
/* get the gamepad state */
PSX_ReadPad(&padbuf, NULL);
/* change coords according to which gamepad button was pressed */
if(padbuf & PAD_LEFT) hx--;
if(padbuf & PAD_RIGHT) hx++;
if(padbuf & PAD_UP) hy--;
if(padbuf & PAD_DOWN) hy++;
/* display text with changes coords */
GsPrintFont(hx, hy, "Hello world from PSX");
GsDrawList();
while(GsIsDrawing());
display_is_old=0;
}
}
return 0;
}Not very difficult, right? Now here is full list of possible gamepad buttons constants:
| Constant | Gamepad key |
|---|---|
PAD_LEFT |
Direction pad left |
PAD_RIGHT |
Direction pad right |
PAD_UP |
Direction pad up |
PAD_DOWN |
Direction pad down |
PAD_L2 |
L2 |
PAD_R2 |
R2 |
PAD_L1 |
L1 |
PAD_R1 |
R1 |
PAD_TRIANGLE |
Triangle |
PAD_CIRCLE |
Circle |
PAD_CROSS |
Cross |
PAD_SQUARE |
Square |
PAD_SELECT |
Select |
PAD_START |
Start |