Seventh Chapter Experience

The main learning in this chapter is the control of light emitting diodes, which in this chapter will accomplish a real Linux driver. The Linux driver is used to control 4 LED lights on the development version. That is, by sending data to the Linux driver, you can control the switch of the LED light.

Writing LED Drivers :

1. Initialize Cdev with cdev_init function, describe device file

struct cdev{

struct Kobject kobj; Objects that encapsulate device files

struct module *owner; Pointers to kernel modules

const struct File_operations *ops; Pointer to file_operations struct body

struct List_head list; Pointer to previous and next Cdev struct

dev_t Dev; Represents the device number, int type, first 12-bit main device number, and the last 20-bit device number

unsigned int count; The requested connection device number range (maximum), which is used when setting up multiple device files

}

void Cdev_init (struct cdev *cdev,const struct file_operations *fops)

{

memset (cdev,0,sizeof *cdev);

Init_list_head (&cdev->list);

Kobject_init (&cdev->kobj,&ktype_cdev_default);

Cdev->ops = FoPs;

}

2, the specified device number with 1 int type, the first 12 digits represents the main device number, the last 20 bits indicates the secondary device number

int Dev_number=mkdev (Major,minor); Major represents the main device number, minor indicates the secondary device number

int major=major (dev_number);

int minor=major (dev_number);

3. Use the Cdev_add function to add a character device to the character device array in the kernel

int Cdev_add (struct Cdev *p,dev_t dev,unsigned count)

{

p->dec=dev;

p->count-count;

Return Kobj_map (CDEV_MAP,DEV,COUNT,NULL,EXACT_MATCH,EXACT_LOCK,P);

}

4. Create a struct class using the Class_create macro

struct class *leds_class = NULL;

Leds_class=class_create (This_module, "dev_name");

5. Create a device file using the Device_create function

The Device_create function is prototyped as follows: struct device *device_create (struct class *class,struct device *parent,dev_t devt,void *drvdata, Const CHAHR*FMT,...)

The Leds_init function is an initialization function of the LED driver:

Static in Leds_init (void)

{

int ret;

Ret=leds_create_device ();//Create a device file

PRINTK (device_name "\tinintialized\n");

}

Module_init (Leds_init);

6. Uninstalling the device files

static void Leds_destroy_device (void)

{

Device_destroy (Leds_class,dev_number);//Remove the character device created by the Device_create function

if (LEDS_CALSS)//Destroy struct class

Class_destroy (Leds_class);

Unregister_chrdev_region (Dec_number,device_number);//unregister character device area

Return

}

static void Leds_exit (void)

{

Leds_destroy_device ();//Uninstall the LED driver's device file

PRINTK (device_name "\texit!\n");

}

Module_exit (Leds_exit);

7. Allocation Register

LEDS_INIT_GPM Function Initialization Register

Call the LEDS_INIT_GPM function in the Leds_init function to complete the initialization of the Register

static int leds_init (void)

{

int ret;

Ret=leds_create_device ();

LEDS_INIT_GPM (0xE);//Initialize Register

PRINTK (device_name "tinitialized\n");

return ret;

}

8, Control LED

Two ways: Through string control (using the File_operations.write function)

and control LEDs via I/o command (using the FILE_OPERATIONS.IOCTL function)

Test LED Driver

The final test led driver, there are several methods:

1. Writing a generic program for testing f/0 control commands

2. Test LED driver with NDK

3. Test LED driver using Java

LED-driven porting

The simplest porting of LED drivers is to compile them under different Lim versions.

　　

Seventh Chapter Experience