.COMP3231/9201 Operating
Systems 2020/T2
Administration
  - Notices
  - Course Outline
  - UNSW Timetable
  - Consultations
  - Group Nomination
  - Survey Results!!
Work
  - Lectures
  - Tutorials
Support
  - Piazza Forums
  - Wiki
Assignments
  - Submission Guide
  - Assignment 0 Warm-up
  - Assignment 1
  - Assignment 2
Resources
OS/161
    - General
    - Man Pages
    - Sys161 Pages
C coding
    - Info Sheet
Debugging
    - Learn Debugging
General
    - "Hardware" Guide
    - R3000 Reference Manual
    - Intro. to Prog. Threads
Previous years
  - 2020 T1
  - 2019 T1
  - 2018 S1
  - 2017 S1
  - 2016 S1
  - 2015 S1
  - 2014 S1
  - 2013 S1
  - 2012 S1
  - 2011 S1
  - 2010 S1
  - 2009 S1
  - 2008 S1
  - 2007 S1
  - 2006 S1
  - 2005 S2
  - 2005 S1
  - 2004 S2
The OS/161 System
Background
OS/161 is an educational operating system developed by the
Systems Research at Harvard group, at Harvard University. It
aims to strike a balance between giving students experience
working on a real operating system, and potentially
overwhelming students with the complexity that exists in a
fully fledged operating system, such as Linux. Compared to
most deployed operating systems, OS/161 is quite small
(approximately 20,000 lines of code), and therefore it is much
easier to develop an understanding of the entire code base.
The complete OS/161 environment consists of three major
parts:
• OS/161 itself;
• System/161, the simulated machine that OS/161 runs on;
• development tools required to compile and debug code
for the simulated machine.
In your assignments, you will be working exclusively on the
OS/161 operating-system source code.
System/161 and the development tools are already installed on
CSE machines — you will not need to modify nor understand
their source code.
OS/161
The OS/161 source code distribution contains a full operating
system source tree, including the kernel, libraries, various
utilities (ls, cat, etc.), and some test programs. OS/161 boots
on the simulated machine in the same manner as a real system
might boot on real hardware.
The assignment specifications will contain instructions on how
to get a copy of the sources for each particular assignment.
Warning: Only use OS/161 sources obtained from the
assignment specifications.
We modify some parts of the environment for local use. Hence,
there are no guarantees that any local assignments will be
  - 2004 S1
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achievable or assessed correctly if you use components
sourced from elsewhere.
System/161
System/161 simulates a "real" machine to run OS/161 on. The
machine features a MIPS R2000/R3000 CPU including an
MMU, but no floating point unit or cache. The number of
CPUs available in the machine is configurable, but we will
only be using a uniprocessor configuration at UNSW. It also
features simplified hardware devices hooked up to lamebus.
These devices are much simpler than real hardware, and thus
make it feasible for you to get your hands dirty, without having
to deal with the typical level of complexity of physical
hardware.
Using a simulator has several advantages. Unlike software you
have written thus far, buggy software may result in completely
locking up the machine, making to difficult to debug and
requiring a reboot. A simulator allows debuggers access to the
machine below the software architecture level as if debugging
was built into the CPU chip. In some senses, the simulator is
similar to an in circuit emulator (ICE) that you might find in
industry, only it's done in software. The other major advantage
is speed of reboot. Rebooting real hardware takes minutes, and
hence the development cycle can be frustratingly slow on real
hardware.
Development tools
The OS/161 environment uses modified versions of the usual
GNU development tools (compiler, linker, etc.), named with
the os161- prefix: os161-gcc, os161-gdb, os161-ld, etc. The
OS/161 build system hides most of the complexity of using
these tools directly. However, you will still need to learn to use
GDB.
You should already be familiar the GDB, the GNU debugger.
GDB allows you to set breakpoints to stop your program under
certain conditions, inspect the state of your program when it
stops, modify its state, and continue where it left off. It is a
powerful aid to the debugging process that is worth investing
the time needed to learn it. GDB allows you to quickly find
bugs that are very difficult to find with the typical printf style
debugging.
Our GDB tutorial is a brief and focused introduction to using
GDB with OS/161.
Details beyond the level you need to know can be found at
http://www.gnu.org/software/gdb/gdb.html.
Working from home
See the wiki for instructions for installing System/161 and the
development toolchain on non-CSE machines. Feel free to
build and install them at home. However, while we make every
endeavour to ensure the tools build and function for you, we
cannot be responsible for them working (or not) on your
machine.
We absolutely will NOT take “It worked for me at home”
as an excuse for submissions not working as expected
during our automated assessment process. If you are not
confident of your submission working at CSE, ensure that
your submission correctly builds and functions on CSE
machines!
Page last modified: 12:56pm on Tuesday, 23rd of February, 2016
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