$Id: README,v 1.123 2007-05-01 05:26:48 debug Exp $

Working on what will become 0.4.6

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Gavare's eXperimental Emulator   --   GXemul 0.4.6
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Copyright (C) 2003-2007  Anders Gavare.


Overview  --  What is GXemul?
-----------------------------

GXemul is an experimental instruction-level machine emulator. Several
emulation modes are available. In some modes, processors and surrounding
hardware components are emulated well enough to let unmodified operating
systems (e.g. NetBSD) run as if they were running on a real machine.

Processors (ARM, MIPS, PowerPC, and SuperH) are emulated using dynamic 
translation. Unlike some other dynamically translating emulators, GXemul 
does not need to generate native code, only a "runnable intermediate 
representation", and will thus run on any host architecture.

The documentation lists the machines and guest operating systems that can 
be regarded as "working" in GXemul. The best working guest operating 
systems are probably NetBSD/pmax and NetBSD/cats.

Possible uses of the emulator include:

 o)  educational purposes, e.g. to learn how to write code for MIPS

 o)  hobby operating system development; the emulator can be used as a
     complement to testing your code on real hardware

 o)  running guest operating systems in a "sandboxed" environment

 o)  compiling your source code inside a guest operating system which you
     otherwise would not have access to (e.g. various exotic ports of
     NetBSD), to make sure that your source code is portable to those
     platforms

 o)  simulating (ethernet) networks of computers running various
     operating systems, to study their interaction with each other

 o)  debugging code in general

Use your imagination :-)


GXemul's limitations
--------------------

 o)  GXemul is not (in general) a cycle-accurate simulator, because it does
     not simulate things smaller than an instruction. Pipe-line stalls,
     instruction latency effects etc. are more or less completely ignored.

 o)  Hardware devices have been implemented in an ad-hoc and as-needed
     manner, usually only enough to fool certain guest operating systems
     (e.g. NetBSD) that the hardware devices exist and function well
     enough for those guest operating systems to use them.

     A consequence of this is that a machine mode may be implemented well
     enough to run NetBSD for that machine mode, but other guest operating
     systems may not run at all, or behave strangely.


Quick start
-----------

To compile, type './configure' and then 'make'. This should work on most
Unix-like systems. If it does not, then please mail me a bug report.

You might want to experiment with various CC and CFLAGS environment
variable settings, to get optimum performance.

If you are impatient, and want to try out running a guest operating system 
inside GXemul, read this:  doc/guestoses.html#netbsdcatsinstall

If you want to use GXemul for experimenting with code of your own, 
then I suggest you compile a Hello World program according to the tips 
listed here:  doc/experiments.html#hello

Please read the rest of the documentation in the doc/ sub-directory for
more detailed information on how to use the emulator.


Feedback
--------

If you have found GXemul useful in some way, or feel like sending me
comments or feedback in general, then mail me at anders(at)gavare.se.