[CSE]  Advanced Operating Systems 
COMP9242 2013/S2 
CRICOS Provider
Number: 00098G

PRINTER Printer-Friendly Version

Milestone 0: Familiarisation

This is a simple exercise designed to get you started on seL4. It contains very detailed instructions, together with the existing source code and the seL4 manual you should have no problem doing it.

Your Environment

If you haven't already you may want to take a look at Sabre Lite Lab to set up your development environment and your Sabre Lite.

Most of the 9242 binaries (eg. cross compilers) are in ~cs9242/crossdev/arm-2013.05. You can add this to your path with:

    export PATH=$PATH:/home/cs9242/crossdev/arm-2013.05/bin
    export PATH=$PATH:/home/disy/bin
    # this one overrides cse's hg executable, so it needs to go at the front of your path
    export PATH=/home/cs9242/bin:$PATH 
FIXME: update for git

You should also modify your .hgrc (in your home directory, create one if you don't have it) to add the following lines, to avoid superfluous hg error messages:

hgext/hbisect = !

If you are lazy you can just use the 9242 command for the cs9242 shell:

    ~ % 9242
    newclass starting new subshell for class COMP9242...
    ~ % arm-none-linux-gnueabi-ld
    arm-none-linux-gnueabi-ld: no input files

Note: Your minicom should default to 115200, 8N1, no hardware flow control. If it doesn't then you will have problems talking to your Sabre.

Building SOS

  • Get yourself a copy of the skeleton SOS. We use Mercurial ("hg") for revision control and encourage you to use it too.
  • hg clone /home/cs9242/public_html/current/project/files/aos-2013
  • cd aos-2013
  • make aos_defconfig
  • make

Getting SOS on non-lab machines

  • If you are not using a lab machine, you will need to ensure that hg is in your $PATH at CSE (as well as installed on your local machine!) before performing a check-out. Put this line in your .bashrc (or equivalent):
  • PATH=/home/cs9242/bin:$PATH
  • Now check out the code:
  • hg clone --remotecmd "/home/cs9242/bin/hg" ssh://YOURLOGIN@login.cse.unsw.edu.au//home/cs9242/public_html/current/project/files/aos-2013

Getting it Going

Booting your Sabre Lite for the first time is easy:

  1. Plug in the Sabre Lite (USB and Ethernet) and reset it.
  2. In a terminal, launch minicom, % minicom.
  3. Build, copy the sos image and reset your Sabre by just typing % make.
  4. You should see a successful boot of the sos skeleton. Now it is up to you to bring an entirely new operating system up, good luck.

Development cycle

We have developed a few tools to speed the development cycle along. The makefile can copy the sos operating system, known as a bootimage to your tftp directory and reset the Sabre. Below is a typical development cycle, assuming the path changes to your login script:

  1. Plug in the Sabre Lite, don't forget the ethernet.
  2. In a terminal, launch minicom, % minicom.
  3. In another terminal, launch netcat, % nc -lup 26706.
  4. Make your changes, (hint: learn cscope).
  5. Build, copy the bootimg and reset your Sabre with % make.
  6. Test your changes.
  7. Repeat from step 4 above until satisfied, or you fall over for lack of sleep.
  8. Ending the minicom session, ^A q, and ^C will end the netcat session.

The Milestone

The example skeleton operating system includes an application tty_test which starts up, prints out its name, and then blocks itself forever.

The example includes a printf implementation that outputs data to seL4's debug console. In fact it uses the seL4 debug API seL4_DebugPutChar. This function should only be used for internal SOS debugging, not as a console for applications, so, your task is to modify the sos_write function to send data through the operating system and across the network to your netcat(nc) console.

The second part of milestone zero is to find a partner for the rest of the project. The project is to be completed, in pairs, unless prior permission has been obtained from the LiC.

Recommended procedure

  1. Read (and understand) the code in apps/sos/src/main.c and the code in the apps/tty_test application directory.
  2. Read the documentation on libserial.
  3. Design a simple IPC protocol to transfer data from the user program to your operating system (Recommended reading: seL4 Reference Manual, Chapter 4 (all), Chapter 9 (Section 9.1, 9.2, 9.3.9, 9.3.10, 9.3.11). Note that an endpoint has already been set up between the tty_test application and sos.)
  4. Write the client side implementation in sos_write.
  5. Change the syscall_loop in main.c to recognise your new protocol, and print out a debug message when you receive one of these messages.
  6. Edit tty_test.c so that it tests your sos_write function.
  7. Change the server side so that it now prints the data to libserial, which will send it onto the network.
  8. Test that all of tty_test's output now goes to the netcat console, not the console debugger.


You will need to demonstrate user applications printing to the 2nd console via libserial, running on the Sabre Lite hardware to the tutor during the demonstration period. You should be prepared to show your tutor which files you modified in your solution, and explain any design decisions you made.

Note that since you do not have any form of memory management yet, your protocol will be fairly simple for now, but should be upgraded as more parts of the system are completed. Your tutor will be particularly interested in the details of your IPC interface with different sized blocks of data etc, and how you plan to improve it in future.

You will let the tutor know who your partner is so that group accounts can be created for you.

Last modified: 28 Jul 2014.