EBC Exercise 26 Device Drivers

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Chapter 8 of the text [1] gives a nice example of a minimal device driver. The purpose of this lab is to implement that driver.

Minimal Device Driver Example


Follow the 5 steps given in section 8.1.4 on page 205. You can get a copy of Listing 8-1 here (ECE497_Listings_for_Embedded_Linux_Primer_Chapter_8). Once finished you will have a file called hello1.c in .../drivers/char/examples and have the kernel configure file and Makefile updated for the new driver. See section 4.4 on page 89 for help with modifying the config files.

Note: There is a typo in Listing 8-2.

If you have created the crossCompileEnv.sh file and sourced it, all you have to do to make the modules is cd to the top of the kernel directory and then:

$ make modules

Mine took a while the first time as it compiles all the modules. The second it only took 31 seconds.

Moving to Beagle

On the beagle edit /lib/modules/2.6.32/modules.dep and add


Then copy the file …/drivers/char/examples/hello1.ko on the host computer to /lib/modules/2.6.32/kernel/drivers/char/examples/ on your Beagle. This can be done with a single command though you may have to mkdir the char/examples directory on the Beagle first.

$ cd …/drivers/char/examples
$ rcp hello1.ko root@beagle:/lib/modules/2.6.32/kernel/drivers/char/examples

I suggest putting the rcp in a file since you may use it several times while developing your code.

Now, on the Beagle, modprobe the module and check the log file.

# /sbin/modprobe hello1
# dmesg | tail -4

You should see your Init message. And then...

# /sbin/modprobe -r hello1
# dmesg | tail -4

should show your Exit message.

Module Parameters

Section 8.1.7 on page 211 of the text shows how to pass a parameter to a module. Modify your hello1.c to take a parameter as shown.

Try passing two parameters.

Module Utilities

Play with the mod utilities listed in section 8.2 on page 212.

Driver Methods

Section 8.3 on page 217 gives a longer example of how to use the file interface with modules. Implement the example. Be sure to fix the unsigned int format error.

Some questions...

  • The major device number 234 is part of a range of unassigned numbers. What is the range?
  • What's the new line added to hello_init do?
  • What does mknod do?
  • How can your driver find what the minor device number is?