Subject: RE: Minimal CP-M SBC design
From: "Chuck Guzis" <cclist at sydex.com>
Date: Sun, 11 May 2008 10:24:57 -0700
To: cctalk at
classiccmp.org
Date: Sat, 10 May 2008 08:26:41 -0400
From: Allison
Do a A>:ASM BIGFIL.AAB and forget the disk in
B: and you remember
why you hate that.
Or doing "ASM BIGFIL.ASM" or even just "ASM". I got into the habit
of using M80/L80 as soon as I got my hands on a copy. DRI assemblers
(even RMAC) weren't any great shucks.
But then I wa an early adptor of hard disk and
from late '80 on
had at least a 5mb drive to avoid that. Is that less authentic?
By the end of 1981 I'd built a system with romdisk and ramdisk
and no floppy or har disk. Was that authentic?
I think I failed to make my point well enough. Almost all the people
who worked with CP/M initially did so in the context of floppy disks.
Someone attempting to duplicate that experience would get a less-than-
authentic experience without that aspect, in much the same way one
would be deprived of the experience of big mainframe iron without the
machine room noise level. Could you get a true experience of running
OS/360 without a card reader? An authentic experience consists of
all aspects of the experience, not just the convenient or pleasant
ones. Without the whole, one gets a "dude ranch" picture.
For the latter without the card reader you couls substitute the tape
or even first floppy based job feeds.
As to CP/M if you want the pain oops wrong disk grab an old PC and
dont use hard disk with DOS. IT's somthing that one likes to
forget quickly.
Floppies and CP/M the major issues were lack of space, not enough drives
and some cases systems that could crunch (on power off or power fail)
media left in drive (data lost). Authentic yes, get as much done NO.
Every ones had to learn those fast and after that it was part fo the
psyche and largely forgotten save for lack of space and not enough dives.
What is
authentic? To me if the platform has 8080, 8085,
Z80, Z180/64180, Z280, or NSC800 it's running on real iron. Of
course if you have a Z380 or eZ80 in native mode or a NEC V20
in 8080 mode those may count too.
No, one gets extra bugs with a V20 that the 8080 never had.
;) but they are Authentic.
1.4 really
didn't even do a DISK bios, it was embedded in the bdos.
the bios for 1.4 was only terminal, punch reader and printer IO.
Yes, it ws a pain to interface any new disk to it.
Not according to my archives. While it's true that the 1.4 BIOS
lacked the configurability of 2.0/2.2 (i.e. there were no DPBs, etc.
to define your own disk format), it contained the disk access code
(e.g. SELDSK, SETTRK, etc.) If you'd like, I can send you a copy of
the CBIOS that came with my Tarbell controller, complete with
Processor Technology video board driver (which I didn't use). It's
remarkable in one aspect--it allows for simulated 2-drive operation
on one drive by prompting for the A: or B: floppy when required.
I have 1.4 for 8" and NS* Horizon (still running!) and their
respective manuals. Your right I forgot that NS* created a
second level bios strictly for the terminal, printer, punch, reader
part of the interface. That part if the ihterface is very lightly
doumented in my Alteration Guide.
CP/M 1.4 had the right idea--it supported only one
diskette format,
so if you had more than 250K of storage, you were pretty much forced
to accommodate this by simulating multiple floppy drives. (Wasn't
there an early system that used an IMI "shoebox" drive for the Apple
II that simulated about 50 floppies?) Where things got out of hand
is when DRI said "Roll your own" with no guidance as to disk format
standards.
It is in 2.0 (deblocking). However their
explanation is thin and
some of the fine details have to be infered by really reading the
code. It was very mysterious when I did it for the first time back
in '80 when I was working with a early sample 765 DD FDC. It was
later that Andy Johnson-Laird wrote The Programmers CP/M Handbook
which covers the subject in much greater detail and has two BIOS
exammples that are very commented.
It's been years since I've chatted with Andy. My acquaintance with
him began after his book, however and I hadn't even realized that
he'd done anything with CP/M.
I'd say he write "the book" that explains things from both the
bios/systems perspective and the applicatiosn programmers eye view.
It's the book I refer everyone too after the Alteration Guide has
confused, narrowed and limited their view of what can be done.
I've always maintained that CP/M was a UI and filesystem mostly
and there was little it prevents and mostly allowed anything.
It did a far job of hardware abstraction and mostly kept out
of the way.
Allison
Cheers,
Chuck