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PSIM 1.0.1 - Model of the PowerPC Environments
Copyright (C) 1994-1996, Andrew Cagney <>.
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
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 <>.
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
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:
while an overview of how to use PSIM is in:
This file is found in:
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.
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.
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
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:
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.
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?
Among other things it does not have an Apple ROM socket.
Could PSIM be extended so that it models a CHRP machine?
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?
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:
For details of the terms and conditions.
Where do I send bugs or report problems?
There is a mailing list (subscribe through at:
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.