From: thad@public.BTR.COM (Thaddeus P. Floryan)
Newsgroups: comp.sys.3b1
Subject: Re: Xinu for the 3b1
Date: 26 Jul 92 21:57:44 GMT
Organization: BTR Public Access UNIX, Mountain View CA

In article <1992Jul23.001609.23161@shibaya.lonestar.org> afc@shibaya.lonestar.org (Augustine Cano) writes:
>I just came across the following in misc.forsale.computers:
>[...]
>Betty ported Xinu to these machines, the boards from which we now use
>as standalone Xinu machines for OS courses. You can get her source
>code with anonymous ftp to ftp.cs.umb.edu in directory /pub/xinu7300

Enclosed is the info on the 7300/3B1/UNIXPC Xinu.  The sources to "XINU"
itself are NOT at ftp.cs.umb.edu

Thad Floryan [ thad@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]

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ftp> status
Connected to bach.cs.umb.edu.
Mode: stream; Type: binary; Form: non-print; Structure: file
Verbose: on; Bell: off; Prompting: on; Globbing: on
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ftp> pwd
257 "/pub/xinu7300" is current directory.

ftp> dir
200 PORT command successful.
150 Opening ASCII mode data connection for /bin/ls.
total 477
-rw-r--r--  1 502      wheel        5085 Jun 18  1991 README
-rw-r--r--  1 502      wheel      421108 Jun 18  1991 XINU.tar.Z
-rw-r--r--  1 502      wheel        9711 Mar 19 21:30 disserver.tar.Z
-rw-r--r--  1 502      wheel       38703 Jun 18  1991 mtip.tar.Z
226 Transfer complete.
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Contents of the README file:


Xinu for the ATT7300 (3B1) and MECB (Motorola Educational Computer Board)

This is an implementation of the Vol. I Xinu for diskless singleboard
68000/68010 systems.  The ATT7300 is the preferred system, having
at least .5M memory vs. the MECB's cramped 32K.

ATT7300 hardware and the Xinu support provided here:

MC68010, 10Mhz
.5M-2M onboard memory, up to 4M with expansion memory
VA space of 4M, monolithic page table (not used here for paging)
RS232 port with software-selectable baudrates to 19.2K baud, with
  NEC7201 SLU (used for Xinu console)
Line clock interrupting at 60Hz, used for Xinu clock.
Keyboard interface with MC6850 SLU--Xinu tty driver for it here, but
  not compatible with the serial encoding from the native keyboard,
  so you need to attach another terminal to use it.
Centronics parallel printer port (start on LPR driver here, fleshing
  it out is a good student project)
Floppy disk--not supported in Xinu, but used to boot monitor/downloading
  system
Hard disk--not supported or needed.  
Realtime clock--not supported in Xinu.
Telephone interfaces--not supported.
Bitmap graphics monitor interface--not supported.

MECB hardware and Xinu support:

MC68000 CPU, 4Mhz
32K memory
2 serial ports, each with MC6850 SLUs, available as Xinu ttys or
  dlcs.  Easy to add a third MC6850 at 0x30001, for 2nd dlc.
  (However running a Xinu net takes more than 32K memory, not so easy)
MC68230 PI/timer:  Timer used as Xinu clock, setup for LPR driver
  using PI.

Changes to Xinu required by this port

A major aim was preserving the original code as far as possible,
so that Comer's text (Vol I) is still highly relevant.  One
problem here is that the ATT7300 has 2 different SLU chips, the
NEC7201 and the MC6850.  To mask the differences, all the required
hardware actions are carried out by macros, and the necessarily
device-dependent entry points such as ttyoin and ttywrite are
now TTYOIN and TTYWRITE, expanding as required to ttyoin7201
or ttyoin6850, etc., so that ttyoiin7201.o68, the resulting
object file, has the macros expanded for the 7201 chip.
One could simplify back to one chip by ignoring the 6850
altogether--it requires making a special cable to be useful.

Development Host Assumptions

We are downloading Xinu from Suns on which we run Gnu C/as/ld, but
nothing added to Xinu has been written to require ANSI C.  So it
should all build with Sun cc or other pre-ANSI C.  The assembler
sources are in Sun/Gnu syntax, not Motorola syntax nor the still
different ATT7300 assembler.  Luckily this is a very small part
of the system.

Turning an ATT7300 into an online standalone system.

The ATT7300 as delivered as a UNIX PC has only a turnkey ROM
program, that initializes the sytem and boots off the floppy
disk or hard disk, normally the file "/unix", but this can be
any executable.  Thus at least a download program needs to be
here--see below for our software.

It is straightforward to attach the DTE port of the ATT7300 to
a serial line, and use whatever system you have to download to
it.  In addition, you need to be able to reset it from the host.
We have one MECB dedicated as a reset server to all the online
standalone systems, and the signal from it needs to be connected
into the reset logic of the 7300.  Note that it uses an RC circuit
to debounce the reset button, so a TTL-type signal needs gain
before being connected into this circuit, unlike the MECB that
uses butterfly-connected gates to debounce its reset button.

Downloading/monitor software on the ATT7300

In libsa_on7300 and tutor_on7300 there are the sources for software
to be built on the ATT7300 running its own UNIX, then written
to a floppy disk to be read in on reset from the development
host.  The "Tutor" debugger follows the command syntax of
Motorola's TUTOR series, doing breakpoints but not disassembly.
There is also "remcom" support for remote gdb built in but not
yet working--maybe by the end of summer.  Getting this working
from a bare machine was the greater part of this effort--once
you can download it's easy to do software work, and it means
you've already got a working serial driver.  The 7300's serial
interface (NEC7201) is ridiculously complicated--I can't imagine
why they chose this particular chip.  The downloading is of
course just one end of the system we use--we can supply the
host end too if you want--pick up mtip.tar as well for this.

Running non-Xinu programs.

The two libraries libsa and libxc together provide a C standalone
programming environment completely separate from Xinu.  The
top-level directory sa_examples has a few sample programs and
a Makefile.  In the top-level sa directory are headers for the
MMU and PI as well as the Xinu-supported parts of the hardware.

Support

As usual, no support is guaranteed, but please write to eoneil@cs.umb.edu
with any problems and I'll try to help.  In particular, although
this implementation is known to Purdue and Doug Comer, and this
method of distribution is OK with them, they have no time to 
support such specific ports as this.

Betty O'Neil   June, 1991

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