Who wants a deep-dive into a tiny aspect of Psion SSDs and their ASICs?

I was using a PsiDrive a couple of months ago to dump a 2MB SSD. However, when I tried to extract the files, my FEFS extraction tool (siboimg) segfaulted halfway through. So, as I was in a rush, I decided to come back to it another day. Yesterday was that day.

My first thought was that it could be a problem with the Pico 2, either with the code or the RP2350 A2 stepping chip. So, a couple of days before, I built a second PsiDrive and put in a Pico 1. But the fault remained with with Pico 1.

Me: I could do with a quick win to get me going again.

Also me: I shall learn a proprietary object oriented dialect of C, where the only way to learn it is to plough through 1150 pages of documentation.

Psion doesn’t have a formal name for the object oriented version of C that it created for EPOC16. I’ve been calling it “Psion OO C”, but the main library that it uses is called OLIB, which contains the root class. The others are:

It’s been a while, hasn’t it?

My work on this project has been relatively sporadic over the past 12 months. I’ve not found it easy to find a balance between this, my day job, and other projects I’m working on. As a result, there have been some relatively intensive periods of work on Psion shenanigans, followed by burnout or other priorities needing to take precedence.

Finally, it’s here! Some proper code for reading SSDs and (eventually) other SIBO peripherals.

I’ve spun off some the Arduino code from SIBODUMP, added the FlashFS code from SIBOIMG, ported it to PlatformIO, and pushed it to GitHub.

So, the TL;DR is:

• Two major bugs squished.
• It works with more boards now (Pico, ESP32, Arduino Nano)
• It’s still uses the Arduino libraries, but it’s now based on PlatformIO
• You’ll need level shifters for 3.3v (I’ve included an example)
• Would regular Raspberry Pi compatibility be useful?
• Next steps
• Discord chats

So, take a look at the code over on GitHub Codeberg, then read on.

A month ago I had never typed a line of C. Concepts like pointers, structs and treating variables as actual blocks of memory rather than abstract values were alien to me. But I really wanted to get into C; I knew that knowing the language would be vital for this project and there was only so long that I could put off learning it. I needed a target.

Karl had already written a Windows app in C# that would extract files from an image of an SSD. The Flash format had been well documented by the fantastic Clive D W Feather in his invaluable collection of SIBO documentation known as The Psionics Files. So I decided to follow in Karl’s footsteps and write an SSD file extractor in C. Something that would be more portable than his C# app, that I could compile on Linux, *BSD, macOS and Windows. And so, armed with a copy of the second edition of K&R and a few pre-ripped SSD images, my journey began.