sim/ppc/README

		PSIM 1.0.1 - Model of the PowerPC Environments


    Copyright (C) 1994-1996, Andrew Cagney <cagney@highland.com.au>.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License
    along with this program; if not, see <http://www.gnu.org/licenses/>.
 

    ----------------------------------------------------------------------


PSIM is a program written in extended ANSI-C that implements an
instruction level simulation of the PowerPC environment.  It is freely
available in source code form under the terms of the GNU General
Public License (version 3 or later).

The PowerPC Architecture is described as having three levels of
compliance:

	UEA - User Environment Architecture
	VEA - Virtual Environment Architecture
	OEA - Operating Environment Architecture

PSIM both implements all three levels of the PowerPC and includes (for
each level) a corresponding simulated run-time environment.

In addition, PSIM, to the execution unit level, models the performance
of most of the current PowerPC implementations (contributed by Michael
Meissner).  This detailed performance monitoring (unlike many other
simulators) resulting in only a relatively marginal reduction in the
simulators performance.


A description of how to build PSIM is contained in the file:

		ftp://ftp.ci.com.au/pub/psim/INSTALL
	or	ftp://cambridge.cygnus.com/pub/psim/INSTALL

while an overview of how to use PSIM is in:

	ftp://ftp.ci.com.au/pub/psim/RUN
or	ftp://cambridge.cygnus.com/pub/psim/RUN

This file is found in:

	ftp://ftp.ci.com.au/pub/psim/README
or	ftp://cambridge.cygnus.com/pub/psim/README


Thanks goes firstly to:

	Corinthian Engineering Pty Ltd
	Cygnus Support
	Highland Logic Pty Ltd

who provided the resources needed for making this software available
on the Internet.

More importantly I'd like to thank the following individuals who each
contributed in their own unique way:

	Allen Briggs, Bett Koch, David Edelsohn, Gordon Irlam,
	Michael Meissner, Bob Mercier, Richard Perini, Dale Rahn,
	Richard Stallman, Mitchele Walker


				Andrew Cagney
				Feb, 1995


    ----------------------------------------------------------------------


    What features does PSIM include?

	Monitoring and modeling

		PSIM includes (thanks to Michael Meissner)
		a detailed model of most of the PowerPC
		implementations to the functional unit level.


	SMP
		
		The PowerPC ISA defines SMP synchronizing instructions.
		This simulator implements a limited, but functional,
		subset of the PowerPC synchronization instructions
		behaviour.  Programs that restrict their synchronization
		primitives to those that work with this functional
		sub-set (eg P() and V()) are able to run on the SMP
		version of PSIM.

		People intending to use this system should study
		the code implementing the lwarx instruction.
		
	ENDIAN SUPPORT

		PSIM implements the PowerPC's big and little (xor
		endian) modes and correctly simulates code that
		switches between these two modes.

		In addition, psim can model a true little-endian
		machine.

	ISA (Instruction Set Architecture) models

		PSIM includes a model of the UEA, VEA and OEA.  This
		includes the time base registers (VEA) and HTAB
		and BATS (OEA).

		In addition, a preliminary model of the 64 bit
		PowerPC architecture is implemented.

	IO Hardware

		PSIM's internals are based around the concept
		of a Device Tree.  This tree intentionally
		resembles that of the Device Tree found in
		OpenBoot firmware.  PSIM is flexible enough
		to allow the user to fully configure this device
		tree (and consequently the hardware model) at
		run time.

	Run-time environments:

		PSIM's UEA model includes emulation for BSD
		based UNIX system calls.

		PSIM's OEA model includes emulation of either:

			o	OpenBoot client interface

			o	MOTO's BUG interface.


	Floating point

		Preliminary support for floating point is included.


    Who would be interested in PSIM?

	o	the curious

		Using psim, gdb, gcc and binutils the curious
		user can construct an environment that allows
		them to play with PowerPC Environment without
		the need for real hardware.


	o	the analyst

		PSIM includes many (contributed) monitoring
		features which (unlike many other simulators)
		do not come with a great penalty in performance.

		Thus the performance analyst is able to use
		this simulator to analyse the performance of
		the system under test.

		If PSIM doesn't monitor a components of interest,
		the source code is freely available, and hence
		there is no hinderance to changing things
		to meet a specific analysts needs.


	o	the serious SW developer

		PSIM models all three levels of the PowerPC
		Architecture: UEA, VEA and OEA.  Further,
		the internal design is such that PSIM can
		be extended to support additional requirements.


    What performance analysis measurements can PSIM perform?

	Below is the output from a recent analysis run
	(contributed by Michael Meissner):

	For the following program:

	long
	simple_rand ()
	{
	  static unsigned long seed = 47114711;
	  unsigned long this = seed * 1103515245 + 12345;
	  seed = this;
	/* cut-cut-cut - see the file RUN.psim */
	}

	Here is the current output generated with the -I switch on a P90
	(the compiler used is the development version of GCC with a new
	scheduler replacing the old one):
	
	CPU #1 executed     41,994 AND instructions.
	CPU #1 executed    519,785 AND Immediate instructions.
	.
	.
	.
	CPU #1 executed          1 System Call instruction.
	CPU #1 executed    207,746 XOR instructions.
	
	CPU #1 executed 23,740,856 cycles.
	CPU #1 executed 10,242,780 stalls waiting for data.
	CPU #1 executed          1 stall waiting for a function unit.
	.
	.
	.
	CPU #1 executed  3,136,229 branch functional unit instructions.
	CPU #1 executed 16,949,396 instructions that were accounted for in timing info.
	CPU #1 executed    871,920 data reads.
	CPU #1 executed    971,926 data writes.
	CPU #1 executed        221 icache misses.
	CPU #1 executed 16,949,396 instructions in total.
	
	Simulator speed was 250,731 instructions/second


    What motivated PSIM?

	As an idea, psim was first discussed seriously during mid
	1994.  At that time its main objectives were:


		o	good performance

			Many simulators loose out by only providing
			a binary interface to the internals.  This
			interface eventually becomes a bottle neck
			in the simulators performance.

			It was intended that PSIM would avoid this
			problem by giving the user access to the
			full source code.

			Further, by exploiting the power of modern
			compilers it was hoped that PSIM would achieve
			good performance with out having to compromise
			its internal design.


		o	practical portability

			Rather than try to be portable to every
			C compiler on every platform, it was decided
			that PSIM would restrict its self to supporting
			ANSI compilers that included the extension
			of a long long type.

			GCC is one such compiler, consequently PSIM
			should be portable to any machine running GCC.


		o	flexibility in its design

			PSIM should allow the user to select the
			features required and customise the build
			accordingly.  By having the source code,
			the compiler is able to eliminate any un
			used features of the simulator.

			After all, let the compiler do the work.


		o	SMP

			A model that allowed the simulation of
			SMP platforms with out the large overhead
			often encountered with such models.


	PSIM achieves each of these objectives.


    Is PSIM PowerPC Platform (PPCP) (nee CHRP) Compliant?

	No.

	Among other things it does not have an Apple ROM socket.


    Could PSIM be extended so that it models a CHRP machine?

	Yes.

	PSIM has been designed with the CHRP spec in mind. To model
	a CHRP desktop the following would need to be added:

		o	An apple ROM socket :-)

		o	Model of each of the desktop IO devices

		o	An OpenPIC device.

		o	RTAS (Run Time Abstraction Services).

		o	A fully populated device tree.


    Is the source code available?

	Yes.

	The source code to PSIM is available under the terms of
	the GNU Public Licence.  This allows you to distribute
	the source code for free but with certain conditions.

	See the file:

		ftp://archie.au/gnu/COPYING

	For details of the terms and conditions.


    Where do I send bugs or report problems?

	There is a mailing list (subscribe through majordomo@ci.com.au) at:

	powerpc-psim@ci.com.au

	If I get the ftp archive updated I post a note to that mailing list.
	In addition your welcome to send bugs or problems either to me or to
	that e-mail list.

	This list currently averages zero articles a day.


     Does PSIM have any limitations or problems?

	PSIM can't run rs6000/AIX binaries - At present PSIM can only
	simulate static executables.  Since an AIX executable is
	never static, PSIM is unable to simulate its execution.

	PSIM is still under development - consequently there are going
	to be bugs.

	See the file BUGS (included in the distribution) for any
	other outstanding issues.