Date   : Thu, 18 Aug 1994 15:14:31 +0100
From   : jfid@... (James Fidell)
Subject: xbeeb 0.1 posted to alt.sources

Thought I'd forward this on to you all in case you don't see it
elsewhere...


Newsgroups: alt.sources.d
Distribution: world
Followup-To: 
From: jfid@... (James Fidell)
Organization: Micro Focus Ltd., Newbury, Berkshire, UK.
Subject: xbeeb 0.1 posted to alt.sources
Keywords: 

I've posted a pre-alpha version of xbeeb, my BBC Micro emulator for
UNIX and X11 to alt.sources.  It is also available via anonymous FTP
from ftp.pipex.net:/incoming/xbeeb/...

Here's the README file :

This is the first source release of my BBC Micro emulator for UNIX and X11.
The emulation is far from complete and much work remains, but I have had
a number of requests to see the code, so here it is.  Remember that it is
very, very, very pre-alpha :-)

The code is known to compile and run on SVR4, Linux and Solaris 2.3.


What has been implemented
========================

All of the instruction set of a standard 6502 CPU.  No 65C02 or 65C12
operands are currently implemented, although I do plan this for a future
release.

The 6522 VIA implementation is almost complete.  The emulation of the
system VIA is sufficient to provide clock interrupts and keyboard handling
for the OS.

The CRTC, Serial ULA and display implementation is complete enough to
provide a reasonable emulation of a MODE 7 display.  X11 fonts for teletext
text, contiguous mosaic, separated mosiac and double-height text are
provided.  I have not completed the other required fonts yet.

The keyboard handling is pretty much there, but not quite perfect as the
Beeb has a somewhat non-standard keyboard layout compared with most I've
used.

Paged ROMs/RAM are supported.

There is a snapshot format for saving the complete machine state.


What isn't supported
===================

None of the bit-mapped screen modes are yet supported.  This will be in the
next release, honest :-)

There is no disk/tape emulation.  This means that although there's a snapshot
format, it's a bit of a pain to find some way of creating them.  I usually
hack the code to do this sort of stuff (did I say it was pre-alpha ?  OK :-)

Sound, serial IO, the ADC, Econet, the FRED and JIM memory-mapped IO pages,
the Tube and User VIA are pretty much all ignored.


Installation
===========

See the INSTALL file.


Running xbeeb
============

To start as if from power-up, just :

       $ xbeeb

or if you want to run a snapshot :

       $ xbeeb <snapshot-name>

The following command-line options are also supported :

       -o <filename>

       Loads the specified file as the OS.

       -p[slot] <filename>

       Loads the specified file as a paged ROM into the given slot (between 0
       and 15).  If no slot is given, then the default is to use slot 15.

       -w[slot]

       Makes the specified paged ROM slot writeable.  This effectively turns
       it into paged RAM.

       -h, -?

       Give help on the command line options.

The emulator checks the specified filename and then XBEEBROOT/roms/<name>
for the OS and paged ROMs.  XBEEBROOT is defined in Config.h.

Some of the less obvious key functions are COPY being emulated by INSERT,
END terminating the emulator and HOME creating a snapshot called home.sst
in the current directory.



Known Bugs
=========

There are probably plenty of bugs I don't know about, though I think that
the CPU emulation is reasonably OK as long as you stick to legal, documented
opcodes.  Here's a few problems I know about...

The CAPS LOCK key has to be pressed twice to ``do the right thing'' in
the emulator.

The keyboard emulation may well still have problems where key/shifted key
character pairs on the BBC Micro keyboard are not the same as those the
keyboard in use with the emulator.

The teletext emulation will break if stressed -- it doesn't always perform
correctly.

The mark/space ratio for flashing teletext is a guess.  I haven't a clue
what it really is.

The emulator probably only works on pseudo-colour X displays.  I haven't
tried it on any others.  Because I was getting brain damage when I was
trying to get the cursor to work, I gave up and went for the sledge-hammer
approach, allocating my own colour map.  It's ugly, but it works and I'll
think of a better implementation later.

The screen emulation flickers because it updates the whole screen when
it changes, rather than just the changed bits, but I haven't worked
out a suitable way to optimise that yet.


General Comments
===============

The code is somewhat ugly -- I started out writing clean modular code
and found that there was just no way I could get anything approaching
the performance I wanted, so I gave up.

Performance is now roughly the same as that of the original machine
on my 486DX2 Linux machine.

Please mail any comments, suggestions, whatever, to jfid@...

James.

-- 
 "Yield to temptation --             |
  it may not pass your way again"    |     jfid@...        
                                     |
        - Lazarus Long               |              James Fidell