Got real in to modding the PS1 for some reason these past couple weeks. I haven’t really made anything new here, but I wanted to document my efforts anyway. All information on this page is only relevant to the fat PS1, not the PSone slims.

DRM in the Sony Playstation

As far as I am aware, There are a couple places where the Sony Playstation implements DRM checks. I must admit I am not an expert on this, and this information might not be completely accurate. I will cite sources wherever I can.

The BIOS/Shell

The PAL and NTSC-J PS1 consoles implement a check in the BIOS where they examine the region code on the disc itself. This region code has to match the region code in the BIOS in order for the BIOS to boot it. The region code is written to a part of the CD that is not normally accessible by conventional CD burners, so you can’t add it yourself. This is sometimes referred to as the “wobble check” or ATIP check.

This can be defeated pretty trivially. The PS1 supports games that span multiple discs, and it only does this check at boot. So, you could insert a disc that has the correct version string, then swap it out for a different one.

Another way to defeat this would be to replace the BIOS entirely with one that does not do this check. OpenBIOS and (presumably) UNIROM do not have these checks. OpenBIOS is open source, and you can see from the source code that it never performs a region check. It just grabs the executable and throws it into memory

The MechaCon (Disc Mech) Firmware

The disc mechanism, or as Sony refers to it, the MechaCon, has its own firmware that can do its own DRM. Luckily for us, Sony implemented some secret CD unlock commands that disable the DRM checks and allow you to boot any game you want. These commands are only present in the US and European models though, not the Japanese ones. There is still modchip support for the Japanese PS1s, and they get around this with some kind of on the fly BIOS patch. To be honest, I am not sure how this works.

Enter the Modchip

There is a fantastic open source modchip called the PsNee. It supports pretty much every single PS1 model in existance, and there is detailed documentatoin on how to install it on all of them. It’s also compatible with a bunch of super cheap Arduino boards and it’s completely open source. Really, it’s the perfect solution in the year of our gourd 2025.

On standard American systems, you only need to solder 7 wires to the PS1 mainboard. European and Japanese systems require four extra wires to be soldered to points connected to the BIOS chip. Again, I am not sure how these wires get around the fact that there are no unlock commands in the non-US MechaCon firmware, but clearly they do work.

My Modchip: The PsNee Mini

In my effort to overengineer everything possible, I created a super tiny PsNee compatible modchip board called the PsNee Mini. It’s 19x12mm and contains an ATmega328pb and associated driver circuitry to run the PsNee firmware. All photos in this post show my modchip. This design is public domain and can be found on codeberg.

The only real benefit of this board is that it is tiny and clean. It’s way smaller than chucking an Arduino Nano in there, and it’s cleaner than deadbugging an ATTiny. Since the other solutions are good enough, I don’t think it will ever get that much use, but I had fun making it!

ODE Replacements

Another way to very effectively defeat the DRM in the MechaCon is just to remove it entirely. There has been a closed source solution on the market for a while now called the XStation that fully replaces the mechanical disc drive and allows you to load your games off of a MicroSD Card. While I don’t know for sure, I assume they did not go out of their way to implement any DRM checks, especially since it can’t actually read real discs anyway. It’s closed source though, and expensive. Boo!

Another project has since come along called the PicoStation. This is an open source alternative to the XStation that’s based on the RP2040. It’s original hardware design leaves a lot to be desired, but hardware developers like ManCloud have since taken the orignal hardware design and created something that can just be ordered fully assembled turnkey from JLCPCB. No need to solder a Pico and order parts from Amazon!

Installing the Picostation is a bit more involved that the PsNee. There are so many wires that the XStation crew has designed a couple of Quick Solder Boards or QSB’s that sit on top of the existing mainboard and let you very easily solder to existing test points without running a bunch of wires.

You also have to, annoyingly, lift a bunch of pins on the CD coprocessor chip. If I didn’t have a rework microscope, I would have definitely swore a lot a more during the rework and probably ripped a couple pads to show for it.

My Changes

I’ve made some small changes to ManCloud’s design, all to make it easier and cheaper to manufacture. There’s a debug connector for the Raspberry Pi Debug Probe, an additional switch for entering the bootloader, and some diode-OR power rails instead of two discrete regulators. I also replaced a couple 2.2k resistors with 1k to remove a part from the BOM, and the switches I picked are much cheaper to buy.

Compatibility with OpenBIOS

I am a huge fan of OpenBIOS, as can be seen on some previous posts. Given that both the modchip and the ODE replacement touch the BIOS in some way, I wanted to see if OpenBIOS running on real PS1 hardware was compatible with these hardware modes. To be honest, this is probably the only valuable work done in this project. The rest is fairly derivative.

I am happy to report that OpenBIOS is compatible with both hardware mods! The OpenBIOS team really did a pretty fantastic job with compatibility here. I read over a fair amount of the source myself, and there’s a lot of this is stupid and bad and buggy, but we implemented it here for compatibility comments in front of very delicately written code.

Further Work

Presumably, OpenBIOS could send the disc unlock commands to the MechaCon itself, negating the need for any PsNee modchip. This isn’t done because piracy is not the goal of OpenBIOS, but it’s something that could definitely be implemented in some kind of fork.

It would also be interesting to see if the PsNee modchip also works in Japanese and European PS1s, or even a Net Yaroze. Those presumably get around the lack of an unlock command with some kind of BIOS patch, but I don’t know how it works and I don’t know if it will be compatible with OpenBIOS. I have a Japanese PS1, but it’s a crazy early model and doesn’t work too well. The physical disc mechanism is totally shot and it outputs a high pitched whine instead of any audio. It’s a PU-7 revision mainboard, the one with an S-Video connection on the back. I’d post the serial number here but unfortunately I found it without a serial number sticker in a crusty bin at the basement level of a HARD-OFF in Akihabara.

I have taken a liking to the PS1. I never had one, but I played it a bunch at my cousins house and have fond memories trying to get to the moon in Rampage: World Tour. I think the low poly graphics and strange zbuffer wobble behavior lends itself well to horror titles and definitely has its own aesthetic, one that I really enjoy.