playstation.md 12 KB
title: Sony PlayStation (PS1/PSX) x-toc-enable: true ...
The PlayStation is a computer like any other. It ought to run all Free Software if you want it to, and you can!
| Specifications | |
|---|---|
| Manufacturer | Sony Computer Entertainment Inc. |
| Name | PlayStation |
| Variants | PlayStation, PSOne, Net Yaroze |
| Released | 1994 (Japan), 1995 (Worldwide) |
| CPU | MIPS R3000 @ 33.8688 MHz |
| Graphics | Custom 3D processor by Toshiba, 1MB Video RAM |
| Sound | 16-bit custom Sony SPU |
| I/O | CD-ROM, analog Audio/Video, Serial, Parallel |
| Memory | 2MB EDO DRAM |
| Architecture | MIPS I instruction set (RISC) |
| Original boot firmware | Sony PS1 BIOS (USA/JPN/EU) |
| Flash chip | 512KB Mask ROM |
Introduction
This uses the free/opensource BIOS developed by the PCSX-Redux team, which you can learn more about here:
https://github.com/grumpycoders/pcsx-redux/tree/main/src/mips/openbios
Build from source
Pre-compiled builds will be in the next Libreboot release, after version 20240612. For now, you must compile it from source, but the Libreboot build system provides automation for this. Please use the latest lbmk revision from Git.
First, please make sure you have build dependencies. The build logic in lbmk has been tested on Debian 12 (x86_64) and you can do this for example, as root:
./mk dependencies debian
The arch and parabola dependencies should also work nicely, if you want
to replace debian with one of those in the above example; you need to get the
cross compiler (mipsel one) from the AUR, which you will see when running e.g.:
./mk dependencies arch
If you have another distro, or you're unsure, the PCSX-Redux project also provide generic instructions for other distros. Please see:\ https://github.com/grumpycoders/pcsx-redux/blob/main/src/mips/psyqo/GETTING_STARTED.md
When you have the dependencies, including mipsel cross toolchain, you can just do this in lbmk:
./mk -b pcsx-redux
This commonly only builds the BIOS part. If you want to build all of PCSX-Redux, you can, but lbmk does not provide automation for this.
Installation
If all went well, you should see openbios.bin located
under the bin/playstation/ (within lbmk). Alternatively, you may be using
a release after Libreboot 20240612 that has it pre-built. Either way is fine.
The openbios.bin file is your new BIOS build.
Emulators
Most PlayStation emulators rely on low-level emulation to execute the real BIOS. The Open BIOS by PCSX-Redux (as distributed by Libreboot) can also be used, and boots many commercial games, plus homebrew.
These emulators can boot many commercial games, with varying degrees of compatibility, and they can also boot any homebrew/opensource games that you might develop yourself, or that others have written.
Simply load your openbios.bin file into the emulator, using the instructions
provided with your chosen PlayStation emulator. You can even freely
redistribute this BIOS, because it's free software (released under MIT license),
which is a major advantage over Sony's original BIOS.
Hardware
Not yet tested by the Libreboot project, but the PCSX-Redux developers have stated that it will work on the real console. It should be noted that the Open BIOS does not seem to implement a memory card save handler at present; you can save and load games, in-game, but there is no built-in program for copying and deleting saves between memory cards. From reading the documentation, it seems that this is essentially a very well-engineered proof of concept that happens to boot a majority of games; some polishing is still needed to make this really useful on a real machine.
The main usefulness of the Open BIOS is that it's under an MIT license, and therefore legal to distribute; anyone wishing to use an emulator can use a compiled copy of the Open BIOS, and distribute it freely without trouble.
You also do not get to listen to music CDs. The quirk with memory cards is easily mitigated in an emulator, because you can simply create different memory card images for each game you play.
It would be nice if a memory card manager program were available, to make this BIOS much more polished, but a number of games have been tested and it's more or less fully reliable in most cases.
Game compatibility
The upstream maintains a compatibility list, here:
NOTE: Google Docs, but an option exists on there to export it for LibreOffice Calc. The list is provided as a spreadsheet.
Remarks about hardware
Modern NOR flash can be used. You specifically want a TSOP-32 SMD/SMT type device, one that operates at 3.3v (tolerance 2.7 to 3.6v), organised into 512KB blocks, for example 512KB x8 is a common part, for example SST39VF040.
Look here: https://oshpark.com/profiles/mi213
This person has designed PCBs that can be used to add a NOR flash, adapting to the pinout of the playstation BIOS. Some early launch model PlayStations used a 40-pin chip but most later ones soon after and to end of life were 32-pin. This page only sells adapters for use with 32-pin boards.
For most boards, the one you want is probably the PS1_Flash_Bios_(A) one.
We do not yet provide instructions for how to install this on real hardware, in the Libreboot project, but this can be done at a future date.
Other mods (hardware)
Video timings
The Open BIOS will not implement any DRM, so it's possible that you might boot out of region games. In an emulator, this is no problem, but it can prove difficult on hardware in a number of situations.
The purpose of these kinds of mods on hardware is typically that the user wants to remove all DRM. Well, there's something many people overlook: video timings out-of-region are often wrong on these machines. The GPUs have two clock inputs (early launch models only have one clock input): one for PAL and one for NTSC. More info could be written here at a later date but these consoles typically don't have a PAL GPU clock on NTSC consoles, and vice versa. You can correct this.
Look up the PS1 "dual frequency oscillator" mod. Without this mod, NTSC games will run slightly slower than they should and have the wrong colours, when booted on PAL consoles (and vice versa); RGB SCART can be used to mitigate the colour issue, but not the timing issue. The oscillator mod is the only solution for the timing issue.
The PAL GPU clock is roughly 53.2MHz, and divides by 12 to create the 4.43MHz PAL subcarrier/colorburst signal; this is needed in composite video for example.
The NTSC GPU clock is 53.693175MHz, and divides by 15 to create the 3.58MHz NTSC subcarrier/colorburst signal; ditto, this is used for NTSC composite video.
On a PAL playstation, Sony hardwired 53.2MHz to both inputs, and on NTSC, wired 53.69MHz to both inputs; that means on NTSC machines, PAL games will run with a 3.579545MHz colorburst signal, and on PAL consoles running NTSC games, the colorburst would be 3.55MHz. Some people suggest hardwiring a 4.43MHz clock to the video dac/buffer on PAL consoles, thus creating what is called a "PAL60" signal, but this is ill advised; ditto wiring 3.58MHz to it (NTSC50).
On most consoles except very early launch/debug models, and very late slim models, the PAL clock is pin 192 on the GPU and NTSC is pin 196 on the GPU. The Dual Frequency Oscillator mod uses a programmable oscillator and taps into the video mode signal off of the GPU to know whether PAL/NTSC is used; it switches the master clock hooked up to both inputs accordingly.
Another method is to cut the line going to the NTSC pin on a PAL console, and wire a 53.69MHz oscillator (at 3.3V, with the output through a 220Ohm resistor) directly to the pin; on an NTSC console, do the same but cut 192 and hook up 53.2MHz to it. The Dual Frequency Oscillator method is easier and therefore recommend, but you can do this other method, which I call DO (Dual Oscillator. Because it's two oscillators!)
By fixing the timings in this way, your region-free console will also have correct timings, thus maximum game compatibility, and colours will always be correct no matter what video cable you're using.
Modchips
If using hardware, you will probably still want a modchip. Many proprietary modchip firmwares exist, such as Old crow, MultiMode3 and Mayumi; these run on PIC chips e.g. PIC12C508A. A special OneChip firmware is often used on PAL PSOne Slims.
There is a free/opensource modchip type called PsNee, which is what Libreboot recommends: https://github.com/kalymos/PsNee
Unlike the other modchips, PsNee runs mostly on Arduino-type boards. You can find more info on its GitHub page.
Although not yet tested by Libreboot, it might be possible to have both the Sony BIOS and Open BIOS, by stacking them on top of each other, soldered pin for pin but leaving the OE/CS pins floating; then, wire up a switch that turns one chip or the other off, so that you can pick which BIOS you want at boot. This might be useful, in case you run into any compatibility issues with the Open BIOS.
A modchip is still desirable, to mitigate copy and region protection in the original BIOS; it may still be required when using the Open BIOS, but this has not yet been confirmed by the Libreboot project.
More hardware testing is planned, but the Open BIOS works perfectly in emulators. Give it a try!
Boot games on SD cards
The PicoStation project provides free firmware for RP2040 devices, which you can solder into a modboard which then emulates the PS1 CD drive. It then lets you boot software (including many games) from an SD card instead of a CD, using disc image files, on a real playstation (the picostation replaces your CD drive).
Not only is this useful in a development context, but it can also be used when your CD drive has worn out and no longer reads discs properly.
Final remarks
Combined with PsNee and PicoStation, the Open BIOS from PCSX-Redux team will turn your 90s PlayStation into a very hackable machine. There is also PSXSDK (which is also free/opensource) allowing for libre game development, also known (somewhat ambiguously) as "homebrew" development. The fact that these old consoles were designed to boot proprietary games is mere coincidence; they are simply computers, fully reprogrammable and as such, Libreboot is happy to provide this support, for the Sony PlayStation
Credit
Thanks go to the PCSX-Redux team for their excellent work reverse engineering the Sony PS1 BIOS.
The two photos shown are as follows:
- PSOne Slim photo was taken from here (the one provided by Libreboot is scaled down and cropped, with color levels enhanced for better contrast): https://commons.wikimedia.org/wiki/File:PS_One_with_LCD.JPG - released under the terms of Creative Commons Attribution-Share Alike 3.0 Unported license
- The cube screenshot is of the PCSX-Redux Open BIOS in operation, on an emulator.
PlayStation, PS1, PSOne and other terms are the trademark of Sony Interactive Entertainment. Libreboot is in no way affiliated to Sony Interactive Entertainment; this page is not an endorsement of Sony Interactive Entertainment, nor do they endorse Libreboot.
PCSX-Redux developers are not affiliated with Libreboot in any way. We simply integrate their Open BIOS into Libreboot because their work is awesome.