ODDAS-LINUX

(a Linux distribution for control and data acquisition)
This mini-distribution is being developed for the ODDAS project.

1. INTRODUCTION

GNU/Linux for the desktop has been rapidly expanding in size as the impact of incredibly cheap disk space and RAM take hold. However, this is mostly due to the addition of large GUI packages. The kernel itself and the basic utilities are still fairly small. Thus they can be used on embedded systems with, say, 8M of RAM and 16M of flash memory serving as mass storage. That was an awful lot of memory a few years ago, but now it is getting tough to find that little memory. When I ordered the PCM-4335 from Aaeon which I used for a test platform for this system, I found it was hard to find an 8M SODIMM, so I went with 16M of memory. I boot with the mem=8M flag so that I can reassure myself that the thing runs with 8M. I also purchased a 16M Disk on Chip to plug into the board, which will eventually serve as the mass storage device, but is currently unused (I'm am now cheating, using an IDE hard drive with a 16M partition).

2. CHOOSING THE FUNCTIONALITY

The system has some basic utilities and networking capability. I tested the networking using PPP over the serial link, but it ought to work with Ethernet as well if you were to get a board with Ethernet on it. The Linux system is a full multi-tasking, multi-user system. With the kernel, utilities and all of the libraries loaded a tad more than 3M of disk space is used. This is made possible by two excellent utilities, busybox and tinylogin.

I chose things assuming that one would rarely be logged on to the console attached to the PC-104 card. But you might need telnet to check up on things, ftp to download new versions of your software, and an http server to update you on system status. Hence, it has telnet, ftp and http servers, but no clients. Also, it has ssmtp, so that mail sent to a user on the embedded system can be rerouted to their home workstation. Cron is available for regular mailing of statistics or running of diagnostics or whatever. Finally, the syslogd is set up so that it can log events on a remote log server.

Here is a brief list of what is included:
 

  • GNU C library - all the functions you could ever want. Well, almost. At least I did not remove the ones that were not in use, as I figured they might be used by a user program.
  • termcap - for attaching with alternate terminals
  • shell - ash, a small shell that acts like an sh should, but without command line editing and completion.
  • cron - for scheduling regularly scheduled events
  • editors - ce, a very small emacs clone. I should offer tiny elvis as an option, I suppose. Generally I would expect that you would edit on your desktop machine and transfer the files with FTP.
  • busybox - see the link above. Lots of useful command line utilities.
  • tinylogin - see the link above. Very small login utilities.
  • ftp server - for transferring files to and fro.
  • telnet - for remote logins over a network.
  • httpd - micro_httpd used to serve up web pages over the network link.
  • mail - mailx and ssmtp allow programs to e-mail notifications to you on your host system.
  • syslog - so you can keep track of what is happening.

    • 3. DOWNLOAD AND BUILD THE ODDAS-LINUX SYSTEM

    The system with all of the source code is on our CVS tree, or if you prefer not to chase a moving target you can download an alpha release here. To build it, all I need to do on my machine is to run the script "build_oddas_linux". If you have installed the same development tools for x86 to x86 as I used, then hopefully that is all that you will need to do as well. Otherwise, you will need to edit the script a bit, to point it at your compilers. If you are running on an x86, you can probably get away with compiling with your native tools.

    Build the kernel which was installed as part of the cross-development tools. It is version 2.2.16, which is the latest stable version at this time. A couple of sample config files are located in the ODDAS-Linux root directory.

    For more information, read the INSTALL directions.

    4. INSTALL THE ODDAS-LINUX SYSTEM

    There are many ways to get software down to an embedded board. The easiest is NFS, but unfortunately my board does not have Ethernet built in (from now on, I'll always make sure my boards have it). Any how, I boot a small rescue system from a floppy, partition and format the disk, then download the real system using floppies.

    Another possibility would be to plug the target's IDE hard drive into your desktop system. Partition it, create the file system, and mount it under /mnt/. Then you can copy the rootfs files over to /mnt. Make sure that you use "cp -a" or you'll mess up all my links and permissions (same goes if you use tar, make sure that you use the "p" option!). If you have the hard drive on /mnt then you can even run lilo, with the "lilo -r /mnt" command, so that the system will boot off the hard drive after installing it on the target.

    Note that the file /etc/ftpusers exists on the system and prevents FTP by root. Perhaps this is a mistake for a system that one never logs onto directly, if you feel that it is then remove root from the list of users in /etc/ftpusers. Or, create a new account using the adduser.

    WARNING: I did not take the time to sort through the device files, so I just dumped all of the ones from my desktop onto this system. As a result, you will use up a lot of i-nodes. Since you cannot add them once the file system has been created, you might want to toss a thousand or so extra -nodes on when you make the file system. See the mke2fs man page for help.

    For more information, read the INSTALL directions.

    5. HAVE A LOT OF FUN!

    I don't know what you plan to do with this system. I plan the following:
  • set it up so it is easy to compile with native tools
  • Make the option to replace FTP and TELNET with OpenSSH
  • boot from DiskOnChip
  • get it to run RT-Linux or  RTAI
  • obtain or write a driver for a PC-104 CAN controller, under RT-Linux.
  • work on the smart sensors for some example project,
  • have the system collect data on its control performance and show it on a web page.


    • Author: Pete Buechler <peter.buechler@home.com>
    Last updated: 22 February 2001.