Re: S-100 68K CPU board status

[lynchaj <lyn...@yahoo.com>]

Hi John!  One approach that might work is to take the CompuPro CP/
M-68K binary image and modify its CBIOS directly.

Since CP/M is comprised of CCP and BDOS which should never change, the
new code would be isolated to the CBIOS.

The first step would be to find out where the CompuPro binary image is
loaded into RAM.  Then build a "loader" program to place it RAM where
it expects to be.

Then inspect the binary image in RAM to find out where the CBIOS jump
table is and locate its first address.  From that we can deduce the
CBIOS entry point and build a new CBIOS binary image that uses the
available IO devices rather than what the CompuPro CBIOS is expecting.

Admittedly this is a kludgy way of making this work but it is a way
out of the "catch-22".  This is how I got the original N8VEM SBC CP/M
working.  I started with a Xerox CP/M-80 binary image, loaded it where
it expected to be in RAM from the bootstrap EPROM, found the CBIOS,
removed it, and replaced it with my own custom version.  It took quite
a while to get it working well enough to boot CP/M reliably but when
it did I could use it to build a more respectable version.

My recommendation is to write just a bare bones CP/M-68K CBIOS using
minimal serial port console IO and a small amount of RAM to make an A:
drive.  Since the A: drive is in RAM it can be loaded as a binary
image.  I put XMODEM in as a program preloaded on the RAM drive so
once the system comes up it can communicate with the outside world.
The resulting binary image to load at boot would be CCP+BDOS+CBIOS+RAM
drive.

I don't know if something like this is possible with the S-100 68K CPU
board but it seems like a path forward.

Thanks and have a nice day!

Andrew Lynch

On Dec 24, 12:46 pm, "John Monahan" <mon...@vitasoft.org> wrote:
> Thanks Andrew. Saw the "CPM68K Source code" however that code is in C and as
> best I can tell needs an running 68K system to put it together. I suppose we
> could look for a cross compiler, linker etc. setup but those kind of things
> quickly unravel.  I was hoping for a CPM86 like image setup where one just
> gets a BIOS shaped up and somehow "splices" it into a CPM68K image.
>
> Enlarging the basic  monitor I wrote (or even the much larger  Motorola
> TUTOR code) to include sector read/writes is not hard/a problem, its
> splicing it on to a CPM68K OS core I'm trying to figure out.
>
> John
>
> John Monahan Ph.D
>
> mon...@vitasoft.org
>