Nut Processor Information

[Thomas Okken]

Back in 2004, I was thinking of writing a Saturn emulator. Like you, I wanted to create a hardware-level calculator emulator, although my motivation was a bit different .I wasn't looking for a let's-reinvent-the-wheel challenge; rather, I wanted to avoid porting Christoph Gießelink's code from Emu42, since it was full of Win32 API calls, and it was multi-threaded, both of which were major obstacles to targeting PalmOS -- and the PalmOS platform was the one that I most wanted to support.

I went looking for Saturn documentation, and found a lot. This isn't surprising since HP actually published documentation on this architecture themselves. However, there were some grey areas, where people commented that certain instructions or behaviors were different between different versions of the Saturn, or even within different production runs of the same product.

I came to realize that writing a Saturn emulator, without knowing the language well, and with no knowledge at all about how the calculator's ROM code works, was doomed to failure, and I gave up on that approach and ended up writing a user-code-level simulator instead.

The state of documentation of the Nut architecture is probably even worse, since this is one for which HP didn't publish exhaustive documentation like they did for the Saturn. (There must have been some, though, or how else did anyone manage to develop Mcode modules for the HP-41?) But my impression is that the people who have managed to create successful Nut emulators tend to be people who know their way around hardware, and feel at ease with a logic analyzer like I do with a debugger.