Booting Linux from EPROM

The process of programming (“burning”) the EPROMs starts out by archiving the small disk drive with tar, then extracting the files onto a clean (zeroed out) file system. By putting the file system onto a clean disk, all unused sectors are zeroed out, and the disk compression works (Listing 1).

To tar the disk image, the “full ”Linux partition was booted, and the 6MB partition mounted. By doing this, the proc file system is not included in the tar. The following commands can be used:

mount -t ext2 /dev/hda2 /mnt
cd /mnt
tar -cpf /tmp/eprom.tar *

To create the (uncompressed) disk image, I used a different machine with a 6MB RAM disk and the following commands:

dd if=/dev/zero of=/dev/ram count=12288
mke2fs /dev/ram 6144
mount -t ext2 /dev/ram /mnt
cd /mnt
tar -xpf ~/eprom.tar .
dd if=/dev/ram of=~/eprom.dsk count=12288

This creates a file (eprom.dsk) which is a sector-by-sector image of the disk. The data to be programmed into the EPROMs is the compressed image. This is done with a program (med.c) which reads the disk image (eprom.dsk), runs the disk compression, and outputs a binary file (eprom.img) which will be programmed into the EPROMs.

med ~/eprom.dsk ~/eprom.img

The EPROM image is then moved to an EPROM programmer and the images are burned.

Fortunately the SBC came with SSD utilities to help build the disk image. The DOS SSD disk has a bare minimum of files in it: the DOS boot files, command.com, autoexec.bat, the keyboard loading program, loadlin and zImage.

Listing 3

Listing 4

The development of what goes on the disk is a large part of the job, and methods need to be developed to minimize this effort. Using the EPROM disk is working well in our application.