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80386 Monitor Progress
Hi Guys, after 3 days of really intensive reading, trying things out etc. I
am now happy to say I have the four 80386 Hardware breakpoint registers now
working in protected mode for our prototype 80386 CPU board. See here:-
You can set breakpoints anywhere in the 4GB address space and single step
from there on, and if required after each step, stop stepping etc.
Probably does not sound like a big dea, l but getting the CPU to work with
interrupts (hard or soft) in protected mode is quite tricky. There are a
few things that were not at all obvious in the few web articles I could
find. I will be traveling Feb 10-15, I am going to try and write up a
complete description of programming the 80386 in protected mode during my
trip. The 80386 is an incredibly powerful CPU, but as best I can tell few
don't dig down deep, since the Operating system/BIOS prevents them from
doing so on a PC.
My 28C256 EEPROM Monitor code is now up to 15,700 lines of NASM code. I
have the monitor arranged so it will work with 8088,8086,80286 and 80386
CPUs. The Protected mode is in a section all to itself since it is true 32
bit code. Finally mastered those darn Descriptor tables!
One final thing, I am thinking of adding (in Real Mode), is the ability to
directly read an XModem file with our Console-IO board and place the code
anywhere in the S-100 bus address space (0- 16MB). Currently I load the
file in from a CPM/Z80 program and then switch CPU's. This way the whole
thing is self-contained. Less keystrokes if you do it all day!