5 May
2008
5 May
'08
9:19 a.m.
Ethan asks:
I am a little unclear, though, about how traditional
CP/M systems
were set up for ROM and RAM. Was it common to use a "shadow ROM"
in low mem at reset, then have the BIOS live at the top of memory?
How did 64K RAM CP/M machines handle the BIOS?
The most traditional CP/M system has a toggle-in front panel and
16K of RAM, Ethan :-).
The much later CP/M systems that had boot ROM's either had them
consuming a small amount of high memory permanently with some
hardware hackery to jump there on a cold reset, or lived in
low mem at reset and had a later stage of the boot process map
them out.
And I am perplexed by your BIOS question. I think you are using
that acronym in a non-CP/M context. If you want to read the
"CP/M 2.0 System Alteration Guide" and rephrase your question I
think we could make some progress.
Tim.
5 May
5 May
5:32 p.m.
On Mon, May 05, 2008 at 09:19:35AM -0400, Tim Shoppa wrote:
Ethan asks:
Ah, yes... I was a bit imprecise in what I was asking about...
I was a bit young for the earliest days of CP/M, so in my mind,
"traditional" was the era of packaged systems like Osbournes
and Kaypros. My mistake. I even have a XOR 5-slot S-100 box
at home, a gift from an older gentleman who happened to mention
something to a relative of mine who works at the Post Office, but
that's a long story - the short of it is that I have enough hardware
to get it working, but no 8" CP/M disks, let alone the right
one for that machine.
I am a little unclear, though, about how
traditional CP/M systems
were set up for ROM and RAM. Was it common to use a "shadow ROM"
in low mem at reset, then have the BIOS live at the top of memory?
How did 64K RAM CP/M machines handle the BIOS?
The most traditional CP/M system has a toggle-in front panel and
16K of RAM, Ethan :-). The much later CP/M systems that had boot ROM's
either had them
consuming a small amount of high memory permanently with some
hardware hackery to jump there on a cold reset, or lived in
low mem at reset and had a later stage of the boot process map
them out.
That's the style I'm thinking of.
And I am perplexed by your BIOS question. I think you
are using
that acronym in a non-CP/M context. If you want to read the
"CP/M 2.0 System Alteration Guide" and rephrase your question I
think we could make some progress.
I'll go hunting for that guide (it sounds exactly like what I was
looking for) when the 'net comes up.
I was originally thinking that even after boot-time, there were
still active routines in ROM that the OS was pointed at, but I'm
sure that perception was colored by how a standard '80s micro'
does things. If, as I now suspect is the case, there's zero need
for ROM code after the initial read from the block storage device
happens, then it seems easy to implement a 64KB RAM system after
all.
From some recent reading of various materials I've
been finding
as I do my research, it does seem that a lot of post-S-100 systems
had 56K or 62K of RAM and 2K or 4K of ROM, still. Since I don't
know specifics, let me ask a general question in the hopes that
someone can figure out what machines and answer accordingly... for
those 2K/4K ROM systems, did any portion of those ROMs get accessed
once CP/M was up, or were they vestigal at that point? I can imagine
some sort of monitor program or such being mapped in for when the
OS got lost in the weeds, but what was that ROM space still good for?
Thanks for helping untangle a conceptual and linguistic lack
of understanding.
-ethan
--
Ethan Dicks, A-333-S Current South Pole Weather at 5-May-2008 at 21:20 Z
South Pole Station
PSC 468 Box 400 Temp -71.0 F (-57.2 C) Windchill -99.1 F (-72.8 C)
APO AP 96598 Wind 6.3 kts Grid 66 Barometer 697.3 mb (9982 ft )
Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html
5:52 p.m.
Ethan Dicks wrote:
...
I was a bit young for the earliest days of CP/M, so in
my mind,
"traditional" was the era of packaged systems like Osbournes
and Kaypros. My mistake. I even have a XOR 5-slot S-100 box
at home, a gift from an older gentleman who happened to mention
something to a relative of mine who works at the Post Office, but
that's a long story - the short of it is that I have enough hardware
to get it working, but no 8" CP/M disks, let alone the right
one for that machine.
This page of mine has information on the XOR computer, including a
couple of disk images that will get you running. The disk images came
courtesy of fellow list member Jerry Wright.
http://www.thebattles.net/xor/xor.html
At the time I obtained the computer, I found very little information
about it on the web, which is why I started the web page. I had
disassembled the monitor ROM before obtaining the original source.
There were a couple spots in the code that didn't make any sense to me,
thinking perhaps my ROM had dropped some bits. Once I had the source
code, I found it really was a bug in the original monitor. While the
XOR used a Z80, the code was written with an 8080 assembler and some asm
macros to handle some Z80-isms. The correct macros were "PUSHIX" and
"POPIX", but the coder wrote "PUSH IX" and "POP IX",
resulting in bad
binary.
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ethan.dicks＠usap.gov -
frustum＠pacbell.net -
tshoppa＠wmata.com