Drivers

See the license of the code (copyright), please do not use the code for educational purposes.

Study on operating systems, creating a device driver.

This project contains a device driver developed for Linux (more specifically a Raspberry Pi). This driver has been rewritten as AALDERING-DRIVER, and you can control a seven segment display with it. Subsequently, a number of additional functionalities were added to make the driver more complex.

It is possible to build the modules using CMake. For this, this 'README' also provides a further explanation of how this is possible, and how these created modules can be added to the kernel.

The following options are supported to control the seven segment display:

• The --display or -d option. This will display a hexadecimal number between 0x0 and 0xF. You can use it as echo "--display 0xA" > /dev/AALDERING-DRIVER or echo "-d 0xA" > /dev/AALDERING-DRIVER.
• The --countup or -u option. This option counts from the number as argument to 0xF. You can use it as echo "--countup 0x4" > /dev/AALDERING-DRIVER or echo "-u 0x4" > /dev/AALDERING-DRIVER.
• The --countdown or -l option. This option counts from the number as argument to 0x0. You can use it as echo "--countdown 0xB" > /dev/AALDERING-DRIVER or echo "-l 0xB" > /dev/AALDERING-DRIVER.

Build and execute

In order to be able to 'install' the driver on the Linux system I will clearly state this in two ways. In the first way, I just use CMake, along with a few other commands. In the second case I just use a shell script, which already runs CMake and make.

Complete with CMake:

1. Create a new build folder in the project. This folder is used for various configuration files, and ultimately the *.ko file. For example, create this folder like this and go into that specific folder (name doesn't matter):

   ../DRIVER_LINUX:~$ mkdir cmake-build
   ../DRIVER_LINUX:~$ cd cmake-build

2. Now all the different CMake files should be generated. This is necessary too eventually.

   ../DRIVER_LINUX/cmake-build:~$ cmake ..

3. Now it's time to actually build the module for the driver. This is done using make for the target driver.

   ../DRIVER_LINUX/cmake-build:~$ make driver

4. Now a *ko file should be available in the folder, for this project this will always be aaldering-module.ko.

   ../DRIVER_LINUX/cmake-build:~$ ls
   aaldering-module.ko   aaldering-module.mod.c   ...
   aaldering-module.mod  aaldeirng-module.mod.o   ...

5. Now this module needs to be added to the kernel. For this we use make again, with the target load.

   ../DRIVER_LINUX/cmake-build:~$ sudo make load

6. The module has been added to the kernel. Check this in /proc/modules and proc/devices. In the latter case, your major device number is also visible.

   ../DRIVER_LINUX/cmake-build:~$ cat /proc/modules
   aaldering_module 16384 0 - Live 0xbf4ec000 (O)
   joydev 20480 0 - Live 0xbf4ce000
   cmac 16384 3 - Live 0xbf502000
   ...
   ../DRIVER_LINUX/cmake-build:~$ cat /proc/devices
   ...
   254 gpiochip
   510 AALDERING-DRIVER
   511 cec
   ...

7. Above you can see the driver, which can be recognized by 510 AALDERING-DRIVER. The number in front must be used to create a special character file associated with the major number 510. You do this with the following command:

   ../DRIVER_LINUX/cmake-build:~$ sudo mknod /dev/AALDERING-DRIVER c 510 0

8. You have to change the access right of the driver with the following command:

   ../DRIVER_LINUX/cmake-build:~$ sudo chmod 777 /dev/AALDERING-DRIVER

9. Now a driver of its own has been added to your Linux operating system! Check this with:

   ../DRIVER_LINUX/cmake-build:~$ echo "--display 0xA" > /dev/AALDERING-DRIVER
   ../DRIVER_LINUX/cmake-build:~$ cat /dev/AALDERING-DRIVER

Sometimes you also want to remove the module from the kernel, as well as the device driver. You do that in the following way:

1. Now make is used again, but then the target unload.

   ../DRIVER_LINUX/cmake-build:~$ make unload

2. Then there is one last step to remove the device driver. Know that this is just a file in Linux, so here's how you do it:

   ../DRIVER_LINUX/cmake-build:~$ sudo rm /dev/AALDERING-DRIVER

Now that the module has been removed from the kernel, as well as the device driver itself, it is possible to go through the above steps again.

Complete with the shell script:

1. The shell script makes the above steps of building a device driver easier. One argument is very important to the script, namely load. This adds a module to the kernel. All other arguments ensure that it is removed if possible.

   ../DRIVER_LINUX/cmake-build:~$ sudo sh load_kernel_module.sh load

2. Now your driver is build and completely inserted into the kernel! How easy is that!
3. Now check if the driver is actually available, and if you see output.

   ../DRIVER_LINUX/cmake-build:~$ echo "--display 0xA" > /dev/AALDERING-DRIVER
   ../DRIVER_LINUX/cmake-build:~$ cat /dev/AALDERING-DRIVER

Again it is possible to remove the device driver and the object for it from the kernel.

1. Any other argument can now be used for the shell script, except load. For clarity, use the unload argument. This ensures that the module is removed from the kernel, and you can add a new one in case of changes, for example.

   ../DRIVER_LINUX/cmake-build:~$ sudo sh load_kernel_module.sh unload

2. Now the device driver is completely unloaded from the kernel! Just as easy as loading the device driver!

Correct functioning

Now a picture will be given of how the driver should function. Here you can see the kernel messages with the command dmesg. To see the output of the character device itself you can just run cat /dev/AALDERIN-DRIVER.

...
[ 3291.010622] [AALDERING DRIVER - MESSAGE] - Initialization started...
[ 3291.010633] [AALDERING DRIVER - MESSAGE] - The function 'register_device()' is called.
[ 3291.010642] [AALDERING DRIVER - MESSAGE] - Registered character device with major number = 510 and minor numbers 0 till 255.
[ 3307.847297] [AALDERING DRIVER - MESSAGE] - Trying to write device file at offset = 0, read bytes count = 5.
[ 3316.149036] [AALDERING DRIVER - MESSAGE] - Trying to read device file at offset = 0, read bytes count = 131072.
[ 3316.149125] [AALDERING DRIVER - MESSAGE] - Trying to read device file at offset = 50, read bytes count = 131072.
bobaa@armpi:~$../DRIVER_LINUX $ echo "--display 0xA" > /dev/AALDERING-DRIVER
bobaa@armpi:~$../DRIVER_LINUX $ cat /dev/AALDERING-DRIVER
--display 0xA