80386 Monitor Progress

["John Monahan" <mon...@vitasoft.org>]

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:-

http://s100computers.com/My%20System%20Pages/80386%20Board/80386%20CPU%20Boa
rd.htm

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!  

Stay Tuned.
John