Nancyvarkey at 11:06, 15 December 2020

2020-12-15T11:06:01Z

Nirmala Venkat: Created page with " {| border="1" |- | align=center| '''Visual Cue''' | align=center| '''Narration''' |- || Slide 1: Welcome slide: | | Welcome to the spoken tutorial on''' Input and Output Co..."

2020-12-10T10:18:28Z

Created page with " {| border="1" |- | align=center| '''Visual Cue''' | align=center| '''Narration''' |- || Slide 1: Welcome slide: | | Welcome to the spoken tutorial on''' Input and Output Co..."

New page

{| border="1"
|-

| align=center| '''Visual Cue'''
| align=center| '''Narration'''
|-
|| Slide 1:
Welcome slide:
| | Welcome to the spoken tutorial on''' Input and Output Control'''
|-
|| Slide 2:

Learning objectives:
|| In this tutorial, we will learn about* '''Ioctl''' function''' '''and
* Data transfer between userspace and kernel space using '''ioctl''' function
|-
|| Slide 3 :

System Requirements:
|| To record this tutorial, I am using,* VirtualBox 5.2.
* Ubuntu Linux 18.04 LTS operating system.
* Linux kernel version 5.0.0-31 generic.
* gedit text editor.
|-
|| Slide 4:

Prerequisites:
|| To follow this tutorial, you should be familiar with:* C programming language
* Basics of Linux kernel

If not, then go through the''' C/C++''' and '''Linux''' spoken tutorials on this website.
|-
|| Slide 5:

Ioctl (input/output control)
|| * It is mainly used to handle some specific operations of a device.

* For example, '''ioctl '''function''' '''can be used to rewind a tape drive.
* By default, the '''kernel''' does not have a '''system call''' for such '''device operations.'''
|-
|| Slide 6:

'''IOCTl() - Example'''

|| In this tutorial, we will learn to transfer data to the driver using the '''ioctl '''function'''.'''
The user program''' test.c''' will send and receive integer data to and from the driver.
|-
||

Point to the folder and file in '''desktop'''
Point to the '''files.'''
|| Go to the''' DeviceDriver folder''' in the '''desktop''' which we have created earlier.
I have created a directory named '''Ioctl.'''
I have saved '''simple_driver dot c, Makefile '''and''' test dot c files.'''

I’ll use these files for demonstration.
|-
|| Slide 7 :

'''Code files:'''
|| The files used in this tutorial are available in the '''Code Files '''link on this tutorial page.
* Please download and extract them
* Make a copy and then use them while practising
|-
|| Open the''' terminal'''

Type >> '''cd Desktop/DeviceDriver/Ioctl'''
|| Open the terminal by pressing '''ALT+Ctrl+T keys '''simultaneously.

Go to the directory where '''Ioctl '''is saved on your system.

Press '''Enter''' key after every command.
|-
||

Type >> '''gedit simple_driver.c'''
|| Type '''gedit space simple_driver dot c.'''

We have already learned the''' open, close, read '''and''' write''' operations on a device'''.'''
|-
| |
| | I have defined the required code to implement the '''ioctl''' functions.
|-
|| HIghlight :

'''<linux/ioctl.h>'''

'''#define MAGIC 'M'#defineSET_DATA_IOW(MAGIC,1u,int)'''

'''#defineGET_DATA_IOR(MAGIC,2u,int)'''
|| We have to include the '''ioctl dot h header file.'''

The '''macros''' used in the '''ioctl''' '''functions''' are defined in this '''header file.'''
'''Write''' and '''Read''' commands are defined with the macros as shown here.
|-
|| Highlight

'''#define SET_DATA_IOW(MAGIC,1u,int)'''

'''MAGIC'''
'''1u'''
'''Int'''
|| '''IOW''' specifies the '''write''' command operation.

'''MAGIC''' is an 8-bit '''magic''' number which is unique to this driver.

'''1u '''specifies the unique command number.

It should not be used by any other driver.

'''Int''' represents the data type of the command argument.
|-
|| Highlight : '''#define MAGIC 'M''''

'''M'''

https://www.kernel.org/doc/Documentation/ioctl/ioctl-number.txt

|| I have used '''M''' as the '''magic''' number in our driver.

For other '''MAGIC''' numbers, refer to this website.
|-
|| Highlight:

static int x = 0;

static int y= 100;

|| I have declared two variables '''x''' and '''y'''.

Data from the user space will be stored in the variable''' x'''.

Similarly, data stored in''' y''' variable is passed to the user space.
|-
|| Highlight

static long mydevice_ioctl(struct file *f,unsigned int ioctl_num,unsigned long ioctl_param);

'''.unlocked_ioctl = mydevice_ioctl'''

|| We have to write the''' ioctl function protocol''' at the start of the program.

Add an '''ioctl''' function pointer '''mydevice_ioctl, '''in the '''file operations structure. '''
|-
|| Highlight

'''static long mydevice_ioctl(struct file *f,unsigned int ioctl_num,unsigned long ioctl_param)'''

'''f'''
'''Ioctl_num'''
'''ioctl_param'''
|| Let us see the '''ioctl function '''now.

It has three parameters as shown here.
'''f '''is the '''file descriptor''' of the appropriate''' device file'''.
'''ioctl_num''' is the '''ioctl command''' that is called from the''' userspace'''.
'''ioctl_param''' is the argument passed from the '''userspace'''.
|-
| |
| | According to the user''' ioctl function''' commands, the '''switch case''' will be executed.
|-
|| HIghlight :
'''SET_DATA'''
'''copy_from_user()'''
| | '''copy_from_user '''will copy the user '''ioctl''' parameter to the '''kernel''' space variable''' x.'''
|-
|| HIghlight :

'''GET_DATA'''
'''copy_to_user()'''
|| '''Copy_to_user function '''will copy the value of variable y from the '''kernel''' space to the user space.
Our program is ready with '''ioctl''' function definitions.
|-
| | Open the''' terminal.'''
|| Save and close the file.

Switch back to the terminal.
|-
||

Type >> gedit '''test.c'''
|| Let’s open the '''user program.'''

Type''' gedit space test dot c.'''
|-
|| Highlight

'''#define MAGIC 'M''''

'''#define SET_DATA _IOW(MAGIC,1u,int)'''

'''#define GET_DATA _IOR(MAGIC,2u,int)'''
|| This program will pass the arguments and commands to the driver.

We have to define these commands similar to the '''driver commands. '''

We will use them in the '''ioctl '''function'''.'''
|-
|| Highlight

'''Static unsigned int g = 0;'''

'''Static unsigned int h = 0;'''
|| The integer type variables '''g '''and''' h''' are defined as shown here.

We will use them later on in this code.
|-
|| Highlight : '''open()'''

'''if(fd < 0)'''

'''File open operation failed.'''
|| '''open '''function opens the '''new_device'''.

If it fails then it will display the failure message and terminate the program.
|-
||

Highlight

ioctl(fd, SET_DATA,&g)<0)

'''ioctl() function.'''
|| The user''' ioctl function''' will internally call the '''driver’s ioctl function.'''

You can use the''' ioctl system call '''only after opening the '''device file.'''
|-
|| HIghlight:

'''fd'''
'''SET_DATA'''
'''g'''
|| The first parameter is the device '''file descriptor number.'''

And the second parameter is the command''' '''that needs to be executed.

The third parameter is the argument to the driver'''.'''

It will display the negative value on failure.
|-
|| Highlight

'''scanf()'''
'''GET_DATA, h'''
'''ioctl()'''
||

We will pass any integer value at runtime to a '''driver''' using the argument''' g.'''
Similarly, we pass the '''GET_DATA''' command to '''ioctl '''function'''.'''

After execution of this''' '''function, we will get the data from the '''driver''' in '''h '''variable.
|-
| | HIghlight '''close()'''
| | The '''close system call '''will close the''' new_device '''file.
|-
|| Highlight

the '''printf messages.'''
| | The printf messages will display the respective information on the terminal.
|-
|| Save the program.

Open the '''terminal'''

Type >> '''clear'''
|| Save and close the file.

Switch back to the terminal.

Clear the screen.
|-
||

Type >> gedit '''Makefile'''
Save a '''file'''.
Click on the '''close button.'''
|| Let us create a '''Makefile''' to compile our '''driver'''.

Type '''gedit space Makefile.'''

Copy the code as shown or you can use downloaded '''Makefile'''.

Close the file and switch back to the terminal.
|-
|| Type >> '''make all'''

|| Now, let us '''compile''' the '''driver'''.

Type''' make space all.'''
|-
| | Type >> '''clear'''
| | Clear the screen.
|-
|| Type >> '''sudo su '''

Type >>''' clear'''
| | Type '''sudo space su '''to be a '''superuser''' and type the system '''password'''.
|-
|| Type >> '''insmod simple_driver.ko '''

|| Let’s now load the driver'''.'''

Type '''insmod space simple_driver dot ko '''
|-
| | Type >> '''clear'''
| | Clear the screen.
|-
||

Type >>''' gcc -c test.c'''

Type >> '''gcc -o test.out test.o'''

Type >> '''./test.out'''

|| Let’s '''compile''' and execute the '''user program.'''

Type '''gcc space hyphen c space test dot c.'''

Type '''gcc space hyphen o space test dot out space test dot o.'''

Type '''dot slash test dot out. '''
|-
|| Highlight
the respective '''printk''' message

Type the '''integer value '''

The '''printk messages.'''
|| The output message shows that the device is opened successfully.

Now, type the integer value that you want to pass to the driver.

I’ll type 500.

The output shows the data copied from the '''driver''' to '''user space '''variable''' h'''.
The print message shows that the device is closed by '''close '''system call.''' '''
|-
| | Type >>''' clear'''
| | Clear the screen.
|-
|| Highlight

Type >>''' dmesg | grep simple_driver'''
Highlight :
Respective''' printk messages.'''
Type >>''' clear'''
|| Type the '''dmesg command '''as shown here.

The output shows that the''' ioctl function''' of the '''driver''' is executed.

It shows the data from the '''user space '''is copied to the''' kernel space driver variable x.'''

Clear the screen.
|-
|| Type '''rmmod simple_driver.ko'''

Type >>''' clear'''
|| Let us unload the '''driver'''.

Type '''rmmod simple_driver.ko'''

Clear the screen. Type exit.
|-
|| Type:

'''cd /usr/include/asm-generic/'''

'''Cat ioctl.h'''

'''Highlight'''
|| In this tutorial, we have discussed IOW and IOR macros.

To know more about other commands, go to the directory '''asm hyphen generic '''as shown:

Let us open the '''ioctl.h''' file.

Type '''cat ioctl.h'''

You can get more details about other commands from the '''ioctl.h file '''
|-
| |
| | With this we come to the end of this tutorial. Let us summarize.
|-
|| Slide 8 :

Summary:
|| In this tutorial, we learnt* Ioctl function()
* Data transfer between user space and kernel space using '''ioctl''' function
|-
|| Slide 9 :

Assignment :
|| As an assignment.# Compile and load '''simple_driver dot c'''
# Compile and execute '''test.c'''
# Pass a different integer value as per your choice
# See the output using '''dmesg command.'''
|-
|| Slide 10:

About Spoken Tutorial Project:
|| * The video at the following link summarizes the Spoken Tutorial project.
* Please download and watch it.
|-
|| Slide 11:

Spoken Tutorial workshops :
|| The Spoken Tutorial Project Team:* conducts workshops and
* gives certificates.

For more details, please write to us.
|-
|| Slide 12:

Forum questions :
|| * Please post your timed queries in this forum
|-
|| Slide 13:

Forum for specific questions :
|| * Do you have any general or technical questions on Embedded Linux Device Driver?
* Please visit the FOSSEE forum and post your question.
|-
|| Slide 14:

Acknowledgment:
| | The Spoken Tutorial Project is funded by MHRD, Government of India.
|-
|| Slide 15:

Thank you slide:
|| This tutorial has been contributed by FOSSEE and Spoken Tutorial Project, IIT Bombay.

This is usha signing off.

Thanks for watching.
|-
|}

Embedded-Linux-Device-Driver/C3/Input-and-Output-Control/English - Revision history

Nancyvarkey at 11:06, 15 December 2020

Nirmala Venkat: Created page with " {| border="1" |- | align=center| '''Visual Cue''' | align=center| '''Narration''' |- || Slide 1: Welcome slide: | | Welcome to the spoken tutorial on''' Input and Output Co..."