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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

CREATE THE DEVICE DRIVER

The header file wtdev2_0.h (all code) is used both by the driver module and by programs that will be making use of the driver. It defines the buffer size, the interrupt, an EOT character, a name for the device, a debug message facility, and a set of IOCTLs that will be used to communicate with the driver.

Similarly, wtdev2_0.c shows the source code for the driver module. The code files are available on the Circuit Cellar web site. Save both files in a convenient working directory.

The corresponding device driver for Linux V.2.2 is only slightly different. Sources for all the programs in this article and the 2.2 version of the driver are in the compressed file weedtech.tgz, which can be downloaded from www.seasurf.com/~jdennon.

To compile this code to create the object module that can be loaded into the kernel by insmod, the compiler needs to be told to access include files from /usr/src/linux/include, and you need to define the __KERNEL__ and MODULE control flags for the preprocessor. It is convenient to encapsulate these details in a little shell script as seen below:

#! /bin/bash
gcc -D__KERNEL__ -I/usr/src/linux/include -DMODULE\
-Wall -O2 -c $1.c -o $1.o

Save this file as mcomp.sh and then mark it executable with the command chmod +x mcomp.sh. When called from the shell prompt using the command mcomp.sh wtdio2_0, the script executes the command:

gcc -D__KERNEL__ -I/usr/src/include -DMODULE\
-Wall -O2 -c wtdio2_0.c -o wtdio2_0.o

This directs gcc to compile the file wtdio2_0.c and create the object file wtdio2_0.o, which contains your kernel device-driver module that can be loaded.