THE MAGAZINE FOR COMPUTER APPLICATIONS
Circuit Cellar Online offers articles illustrating creative solutions
and unique applications through complete projects, practical
tutorials, and useful design techniques.

EMBEDDED NETWORK APPLINCES WITH LINUX

by Greg Ungerer

Start ý A Closer Look ý Why Linux? ý The Building Process ý Microcontroller Linux ý Porting the Application Set ý Debugging ý Future Looks Bright ý Sources and PDF

PORTING THE APPLICATION SET

No kernel is useful on its own. An application set is required to take advantage of the kernel services. The amount of application software available for Linux is staggering. In any embedded system, such as our low-cost embedded network appliances, only a small set of software will be required.

The NETtel application set leans heavily toward network utilities. The core is the set of network configuration and management tools. This includes the commands that configure individual network interfaces (ifconfig, pppd, diald) and set up network addresses and routes (route, ipfwadm, dhcpcd), network services (telnetd, httpd), and Virtual Private Networking (PoPToP).

There is also the usual set of utilities that you would associate with any Linux systemýa shell (albeit, a small one), init program, login, ping, and more. There are not too many limits to what can be ported to ýC-Linux on the ColdFire processor.

One noteworthy application suite is the web server and associated back-end management code (cgi-bins). It is the core of the user interface for administrating the NETtel. Because embedded network appliances generally have no screen and keyboard, the logical method of configuration is through a web browser. A web server and pages can be a surprisingly lightweight and powerful method of configuration.

Given the serious network facilities of the NETtel and ýC-Linux, it is no surprise that network file systems can also be used. Both NFS and SMB shares are supported and can be mounted and un-mounted using ports of the standard Linux tools.

HARDWARE AND SOFTWARE INTEGRATION

The majority of embedded systems are designed for custom hardware platforms. This means that there is almost always a development phase that will entail porting and debugging the system and application software on the target hardware. If thereýs not a custom hardware platform, then almost certainly there will be some custom peripheral hardware to support.

This specialization of purpose and tasks makes embedded network systems unique. Once again, by using freely available operating software such as Linux, it is an easy job to get done quickly. All source code is available, and you have complete freedom over which parts of the kernel are modified to best support the embedded hardware platform.

Another distinct advantage of using Linux is that any newly created applications can be implemented and tested on a Linux workstation. This makes application-level debugging simple and less time-consuming. The completed and tested applications can then be integrated into the embedded environment.

PREVIOUS • NEXT