WIP: 16C firmware hack for more memory

[brouhaha]

(03-12-2023 08:32 AM)brouhaha Wrote:  I think I've now got a handle on adding float mode operations to the normally integer-only instructions as Garry suggested. I need to do more testing to make sure I haven't broken the integer operations.

Now I'm back to 16C microcode hacking after the side quest on the LCD segment to hex program. The purpose of that was to save me perhaps 10 minutes of time writing the code that does this (shown by my Nonpareil simulator):

   

Or shown by running the same hacked firmware on a SwissMicros DM16L:

   

What you see there is that I've patched the microcode that decides whether a function can be executed in FLOAT mode. The calculator is in FLOAT mode, and I've pressed "f SL, which is normally completely ignored in FLOAT. My patch got control, and displayed "FL OP" and a three digit hexadecimal code identifying the specific function, in this case "15A". (This isn't the actual program opcode for SL; when executing from the keyboard, the opcode is not available by the time my patch exeuctes.)

So instead of spending ten minutes figuring out which bits to set in the LCD control registers to display "FL OP", I spent two weeks of spare time writing a program to do it for me! Here's what that program shows, including the 15C user code instructions that could be used to generate the same display on a 15C:

   

Unlike the "FL OP", the digits "15A" are decoded using the 16C's internal hexadecimal-to-seven-segment routine.

An interesting thing to note is that the standard 16C microcode never displays "L", and yet the SwissMicros ARM firmware recognized them and converted them into its internal character set (maybe ASCII?), and then displays them correctly in its bitmap font. I suspect that this happens because SwissMicros made synthetic programing on the 15C work, where such displays can be generated.