Character Devices (iii) and Debugging methods

Llseek:

-einval Illegal (invalid) parameter

Current Position File->f_pos

Seek_end Pcdevp->data_len

The defined position is within your location.

how to deal with : Finally make a save File->f_pos = ...

How to drive LED lights: Look at the schematic, if you want to let the led light on the corresponding port output corresponding level if it is led Light one end of the ground, then make it this side high level, If the next transistor is to consider the transistor conduction, and vice versa ...

Programming makes The CPU has the corresponding pin set as the output pin.

Control the PIN output high or low level

Read The CPU manual sets the appropriate registers such as:cpc1con gpc1dat gpc1pud

There are two ways to control the corresponding GPIO pins under Linux

1) Direct operation of the appropriate registers

2) GPIO Operation Library functions provided by the kernel

control in user space in two ways LED Light, off

1) ,dev/led0 dev/led1 ....

Cdev0 cdev1 ....

Fd0 =open ("/dev/led0", O_rdwe)

Ioctl (Fd,cmd,data);

Ioctl (fd0,1,0)

....

2) /dec/led/

Cdev

Fd0 =open ("/dev/led0", O_rdwe)

Ioctl (Fd,cmd,data);

IOCTL (fd0,1,0) or ioctl (fd0,1,1)

....

Include header file

#include <asm/gpio.h>

#include <plat/gpio-cfg.h>

What role does Cdev play in the driver program? Bridge function?

User Space Kernel space

Open Xxx_open

*gpio Application

Gpio_request (,);

Gpio_free (unsigned gpio)

Debugging the Kernel

Printk

PRINTK will print the information to the console or the /var/log/message file

when developing drivers, a large number of PRINTK are often added to the auxiliary mode

when releasing drivers, you should remove the addition of a large number of PRINTK statements

Code See: http://songmao.blog.51cto.com/11700139/1876798

using the PROCFS file system

file System Procfs is also often used by the kernel to bring information to the user, which can be used in device drivers

Output Debugging information

refer to the previous file system and device file system for details on the procfs file System

Oops

Please see: http://songmao.blog.51cto.com/11700139/1877971

Kgdb

kernel collapse value

<8f0000b8>

The code crashes in the kernel or in the xxx.ko file Code

cat/proc/kallsyms > 1.txt

code crashes in xxx. which function of the C file

arm-linux-objump-d Vmlinux >3.txt

as Xxxx_open

PUSH{R4,R5,R6,R7,FP,IP,LR,PC}

F3997b80 0000000 f34eldf4 ....

Chrdev_open->xxx_open

PUSH{R4,R5,R6,R7,FP,IP,LR,PC}

......

modal core file

Ulimit-a

Ulimit-c Unlimited

GDB A.out-c Core

Please see: http://songmao.blog.51cto.com/11700139/1877998

This article is from the "Mao Scattered People" blog, please be sure to keep this source http://songmao.blog.51cto.com/11700139/1878001

Character Devices (iii) and Debugging methods