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                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 2 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, write to the Free Software
    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 

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


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 2 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.