26 Oct
2018
26 Oct
'18
9:33 a.m.
On 10/25/2018 10:46 PM, Jon Elson wrote:
On 10/25/2018 02:24 PM, allison via cctalk wrote:
I come from the dark ages first work project was 8008 based, when it was
new.
My first stab was 74181 ALU based and was trying to do z80 faster than
4mhz... no hope there and
feature creep made it not z80.? I worked a little monitor to make it
useful but it gave me the core
understanding of CPU and how they work.?? It was fun developing and
deciding I could change an
instruction to make coding easier.
I also did a simple machine based on a simplification of the basic
microcontroller of the RX01.
It had two instructions Jump CC and DO xxxx? It was more than enough to
be a Harvard machine
programmed at the microcode level.
I did those to bridge the college simple logic and sequential circuits
and their jump to programing
a computer with the bit in the middle missing.
Likely make a fortune off my stockpile of 2901s.
Building machine
from the earth up is not that hard, software to make them useful is a
big deal.
Yes, and that's where my 32-bit 2903 project started to bog down.?
I
knew some people, OS security was a total joke, so I COULD have just
stolen OS 360 MVT, but REALLY, who would do that to themselves?
I had a few more bits of logic to wire in, to make a 256-way branch
from the OP-code field of the instruction register to decode
instructions, and from the register fields of the instruction register
to OR into the register address.? Then, I had to write the microcode.?
I'd done some small test bits of microcode, including the multiply,
and that worked.? (IIRC, the 2903 has an extra shift register, so it
can do the multiply step in one CPU cycle, the 2901 takes 2.)
Well, after that, I had a big decision to make.?
Should the memory be
on the system bus, like PDP-11 and VAX, or part of the CPU, like
IBM-360 and PDP-10?? Then, I had to get memory wired to the bit slice
system, and then build peripheral controllers.? I had a very rough
concept scratched up, about 30 chips to make a microcoded 16-bit
machine, using fast EPROMS for the control store.? A SCSI interface
would be pretty trivial, but a read-after-write mag tape control and
an 8-channel serial multiplexer would be much more complicated
project.? THEN, the big stuff would come, I'd need an OS and language
compilers.? I could probably whip up a version of CP/M with
hierarchical directories and time/date stamps, and maybe a simple
editor, but the WHOLE REASON for this project was to move up to modern
high-level languages.? And, I had badly underestimated how difficult
that might become.? One scheme might be to start with my CP/M-like OS,
and build a wrapper program that would allow me to run OS-360
compilers and linkers with whatever object libraries they needed, and
then use them to compile something more to my liking like Pascal.??
But, it was all looking like a LOT of work.
If I ever do another ground up machine its likely to be a OIS, a move
machine.? They are simple and can
be low parts.? They are the RISC of the RISC.
As to chip based the list is [6100, 6120, 9900, 8080, 8085, 8086, z80,
1802, SC/MP, SC/MPII-8073,
6800, 6809, 6502, T-11] as they say long.?? Some I still use namely
8039,? 8085, z80, and 1802 and on
occasion the 6100 (cmos pdp8).? with older CPUs and newer memory the
resulting machines are
interesting and often fast for their type.? Things like large megabyte
Flash makes cp/m without physical
disk remarkably fast (large flash as disk) and simple.
I still run several CP/M machines (S100 and single board plus Kaypro
4/84++) and the PDP11 is mostly running
RT11 but on occasion I load up V6 Unix RL02 pack.? The vaxs are a small
(10way LAVC) mostly running
VMS5.4H.
So, I managed to clone a Nat. Semi 32016 system and
got it running,
but it was amazingly slow.
I suspect that my kluged memory interface was not fully optimal, but
even the original that I copied was pretty slow.? Then, I spent BIG
BUCKS to buy a uVAX-II CPU board from a broker, and was finally in HOG
HEAVEN!? It was certainly fast, almost the speed of the VAX-780's I
used at work, and ALL MINE!
I have the luxury of being there and leading edge for Altair by time 79
rolled around I was PDP11
and would later work in DEC engineering.? By the late 80s I had a nice
PDP11/23 of my own and
not long after a collection of VAX systems that I have to this day.? To
this day VMS is the OS in my
mind though Unix V6, V7(PDP11) and Ultrix(VAX) are around fro the DEC
hardware and Linux on
the desktop.
My idea of doing stuff is a Rpi-3B running a copy of linux on batteries
as a full boat laptop machine.
The Rpi may not be lightning in a bottle but its posting this email!??
What to I do for fun 8039,
PIC or Atmega328P for embedded projects.? One of these days a laptop
running RT11 on one of
the T-11s (PDP-11 chip) I have would be a eye catcher, I'll have to make
the terminal/screen
from a Atmega as hardware for modern LCDs of any sizes
and resolution
(aka 80x24) needs a
lot of hardware to do that.
So, that's my story.
Mine is at best a few snapshots in time.
Allison
Jon