|Re: HP nut CPU and illegal instruction sequences|
Message #9 Posted by Håkan Thörngren on 5 Jan 2010, 1:56 a.m.,
in response to message #8 by Monte Dalrymple
I have so far studied old HP documentation, Doug Wilder´s QuinTable.pdf, David's assembler manual, the Monte Dalrymple's "Inside the NUT CPU" and "NEWT Microprocessor Technical Manual".
The G register and pt=13 thing I have stumbled over myself by accident way back before I even saw it documented. It is well explained in the Newt paper as well as David's assembler manual.
David also explains the C=C|A and C=C&A bugs, but the description is
not the same as I saw in QuinTable.pdf. I will need to experiment with it myself a bit on real hardware.
Non-BCD numbers in decimal mode arithmetics behavior is tested by the service module. I found this out when I tried the service module
on my emulator. (I did it wrong initially).
Anyway, I feel there is a reasonable complete understanding of many of the things going on. The darkest corner seems related to the class 2 (arithmetic) instructions being followed by certain other instructions mystery.
Many thanks, I will keep the information I have collected so far in mind when I can power up my MLDL later for some experiments.