New subject: More Bringing up a CPM

27 May 1999

Yes, '81 was pretty late . . . CP/M-86 came out then, as did PC-DOS.
Within a few years, nobody wanted to be limited by the same systems they
coveted only a few years earlier.  By '81, the Apple][ could be equipped
with a Z80 board, a "real" FDC (Sorrento Valley Associates ?) an 80x24
display, and a hard disk if you could afford it.  I recently sold the
prototype of the original Apple HDC I made up in the spring of '81 together
with my first ST-506.
Those were the days . . . <sigh>
Today I can still run CP/M but at an effective clock rate of 83MHz on my
notebook . . . designing hardware involves thousands of lines of HDL, weeks
in front of a simulation, and when it's done, I can't even hook up an
instrument small and fast enough to inspect it because even our government
can't afford one.  One has to design circuits with 25% overhead so they can
be inspected.  Oh, well . . .
Dick
-----Original Message-----
From: Allison J Parent &lt;allisonp(a)world.std.com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Thursday, May 27, 1999 8:54 PM
Subject: Re: Re[4]: Bringing up a CPM
...
 <If you're writing your own, it might be well to
keep in mind that the BIOS
<used in several late-generation CP/M systems used device drivers which coul
...

It was late generation in 1981!  I started doing it then.  CPM had a formal
product called CP/M+ (CP/M3.0) to extend that idea.
<California Computer Systems (CCS) had a pretty nice boot process in which
<they loaded a skeletal BIOS in a 32K CP/M, since 32K was the smallest memor
...
 <in which they claimed they could run.  It wrote
that to the boot blocks,
Actualy it was 20k for cpm2.2, as it was distributed as a 20k system that
you would run movcpm on to get the xxK version you wanted.
<then, under the control of that skeletal system, they loaded a "full-size"
<(you get to define that!) CP/M and transfer control to it.   It's pretty
<solid and makes the preparation of a bootable disk a straightforward if no
<a quick process.
Yes and they were doing it a long time back, Compupro too.  Kaypro was one
of the few "boxed" system that had the rom mapped to get a large TPA.
<IIRC, the XEROX 820 used a swapped-in BIOS which lived in PROM and was
<mapped into the TPA during file transfers, or something on that order.  If
Classic.
<your machine can handle that, it saves on BIOS size, especially tables, etc
...
 <and, generally speaking, if the READ operations
from the TPA are from
<temprorarily mapped-in PROMs, you can overwrite the TPA in the event you'r
<loading overlays, with complete impunity.  That way your blocking/deblockin
...
 <buffer space can still reside in high memory.
An IMSAI can neither handle that nor not handle that.  The basic design
had no rom!  To do that you need a prom card with a little bit of hardware
to map it with an IO port.
The key here is to get a working system in whatever space... Why, it's the
development platfrom for itself.  Once you have it running and can poke and
understand it the improvements will come.
Allison