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Plan of Attack

In the case of the NSLU2, the Flash is split into four parts :

  • Redboot
  • System Configuration
  • Kernel
  • RAM disk

The Redboot portion is a bit like a PC's BIOS; it initializes the hardware and starts everything from power up. The System Configuration is where persistent variables such as the box's IP address are stored. The Kernel is the Linux operating system image, and the RAM disk is where all of the libraries, configuration files, scripts and executables such as the web server are stored . The RAM disk is what we'll need to modify if we want to automatically start our new processes.

The basic idea is that we'll take a firmware image, split it into its component parts, change the RAM disk portion, put it back together, and reinstall. Easily said, but not so easily done. Any missteps will create what is known as a brick, i.e. a dead piece of equipment that's not much more useful than masonry.

NOTE!Warning: If you want to follow along with this article, you'll have to accept the very real possibility of destroying your box and most certainly your warranty. If you destroy your box, please don't take it back to the store. We don't want to discourage Linksys from creating devices that people can tinker with!

NOTE!NOTE: A method to add a serial port to the NSLU2 has been documented. With a serial port, a box with a bad Flash can be recovered. Adding a serial port requires soldering and is beyond the skill of this author and the scope of this article.

Breaking news: The existence of a method to telnet into the RedBoot loader has also been uncovered. This too could assist in the recovery of a bad Flash without having to break out the soldering iron. For information on recovering from a bad Flash using either a serial port or telnet, see the NSLU2 developers mailing list.

Still here? OK, let's dig in. On my Linux system I created a work directory called myFlash. Create your own, and then inside your work directory, download a Flash image from Linksys. After unzipping the file, you should have a release notes file and a Flash image: NSLU2_V23R25.bin.

Now we'll need a tool to split the file into its parts. The tool we'll use, called splitnslu, was developed by Brian Lantz, but I cached a copy on my website since it may be undergoing changes. Fetch it from here. After untarring it ,you should have a README file, a .c file and a Makefile. The Makefile has several useful targets, but for our uses, we're going to do all of our operations by hand so it's clear what is going on.

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