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LINUX DRIVES WEEDER I/O BOARDS

by Jack Dennon

Start ý Create the Device Driver ý Create the Device ý The Order of Things ý Load the Device Driver ý Call the Test Program ý Remove the Device Driver ý Sources and PDF

THE ORDER OF THINGS

To keep things orderly, there is a list of officially assigned major numbers maintained by H. Peter Anvin (who may be reached at hpa@zytor.com). My Linux system has a copy of that list stashed in the file /usr/src/linux-2.0.30/Documentation/devices.txt. You may have a more up-to-date devices.txt file in the corresponding directory on your own Linux system. Table 2 shows an excerpt from that file. Major number 120 is unused and is reserved for LOCAL/EXPERIMENTAL use, so that is the number I'll use here to create a device file directory entry. Although you would normally gather all the special device files in the directory called /dev, while testing new code it is convenient to use the current working directory.

Use the exit command to exit the root shell and restore your normal user state. The command ls -l c* should, at this point, show that you have the device file entries shown below in your current directory:

crw-r--r-- 1 root root 120, 1 Aug 16 14:56 com1
crw-r--r-- 1 root root 120, 2 Aug 16 14:56 com2
crw-r--r-- 1 root root 120, 0 Aug 16 14:56 com_dev