Prime Reverse-Engineering

[Claudio L.]

(02-08-2015 08:34 PM)Han Wrote:  Perhaps there will be similar projects for the HP Prime. However, in order for that to fully take place, I imagine that we would need HP to give us low-level access somehow (such as was done for the HP48 through HP50 series) in the form of SASM/MASD.

HP won't provide any low-level access on a device certified for exams.

A complete firmware replacement (repurposing the device), however, is not so far fetched.

debrouxl custom firmware already proved a few things:
* Alternative ROM files work just fine.
* Either there's a 1:1 mapping of the hardware or the MMU is disabled.

What puzzles me is why after 6 months nobody took that firmware and tried to push the project forward (?).
Here's a short roadmap for the next "baby step" if anyone is interested (be happy to do it myself but I don't have a Prime):
* Add the ability to write text on the display, almost trivial.
* Dump hardware registers: GPIO first (blocks GPF and GPG most likely as other banks have other uses for the pins), look for a block of 5 to 8 pins set to inputs and that's likely the keyboard rows/columns. Only a few external interrupts can wake the CPU, so looking at which GPIOs have the interrupt enabled will hint at the ON key (GPF block), others will be close.
* Write a simple keyboard scanning routine.
* Write a simple console for interactive sessions with 2 commands: PEEK and POKE.

Interactive PEEK and POKE would pave the road for everything else.

Claudio