ds1620混杂设备驱动

下面分析一下数字温度计DS1620的驱动程序。先从网上找到其数据手册，看看它的功能，再找到时序图片一下。这样有利于分析驱动，再套用上linux的驱动框架就可以了。

同样，先找驱动的入口和出口，看看他们都做了什么。

module_init(ds1620_init);

module_exit(ds1620_exit);

先来看一些常量的定义吧

/*

* arch/arm/include/asm/therm.h: Definitions for Dallas Semiconductor

* DS1620 thermometer driver (as used in the Rebel.com NetWinder)

*/

#ifndef __ASM_THERM_H

#define __ASM_THERM_H

/* ioctl numbers for /dev/therm */

#define CMD_SET_THERMOSTATE 0x53

#define CMD_GET_THERMOSTATE 0x54

#define CMD_GET_STATUS 0x56

#define CMD_GET_TEMPERATURE 0x57

#define CMD_SET_THERMOSTATE2 0x58

#define CMD_GET_THERMOSTATE2 0x59

#define CMD_GET_TEMPERATURE2 0x5a

#define CMD_GET_FAN 0x5b

#define CMD_SET_FAN 0x5c

#define FAN_OFF 0

#define FAN_ON 1

#define FAN_ALWAYS_ON 2

struct therm {

int hi;

int lo;

};

#endif

定义了一些常量寄存器的值：

/*Definitions for DS1620 chip */

#defineTHERM_START_CONVERT 0xee

#defineTHERM_RESET 0xaf

#defineTHERM_READ_CONFIG 0xac

#defineTHERM_READ_TEMP 0xaa

#defineTHERM_READ_TL 0xa2

#defineTHERM_READ_TH 0xa1

#defineTHERM_WRITE_CONFIG 0x0c

#defineTHERM_WRITE_TL 0x02

#defineTHERM_WRITE_TH 0x01

#defineCFG_CPU 2

#defineCFG_1SHOT 1

staticint__init ds1620_init(void)

{

intret;

structtherm th, th_start;

这个什么东东？？？？

if(!machine_is_netwinder())

return-ENODEV;

这个是设置一些参数？复位，配置，停止转换。

ds1620_out(THERM_RESET,0, 0);

ds1620_out(THERM_WRITE_CONFIG,8, CFG_CPU);

ds1620_out(THERM_START_CONVERT,0, 0);

/*

* Trigger the fan to start by setting

* temperature high point low. This kicks

* the fan into action.

*/

ds1620_read_state(&th);

th_start.lo= 0;

th_start.hi= 1;

ds1620_write_state(&th_start);

msleep(2000);

ds1620_write_state(&th);

这里是注册一个混杂设备（混杂设备就是不知道如何归类的)

ret= misc_register(&ds1620_miscdev);

if(ret < 0)

returnret;

这里创建/proc文件系统节点，方便从/proc中获取信息，这样就不用写标准的测试程序了。

就不用走那套老的程序open(),read(),write(),close().

#ifdefTHERM_USE_PROC

proc_therm_ds1620= create_proc_entry("therm",0, NULL);

if(proc_therm_ds1620)

proc_therm_ds1620->read_proc= proc_therm_ds1620_read;

else

printk(KERN_ERR"therm:unable to register /proc/therm\n");

#endif

读取一下当前状态，输出一下信息。

ds1620_read_state(&th);

ret= cvt_9_to_int(ds1620_in(THERM_READ_TEMP, 9));

printk(KERN_INFO"Thermostat:high %i.%i, low %i.%i, "

"current%i.%i C, fan %s.\n",

th.hi >> 1, th.hi & 1 ? 5 : 0,

th.lo >> 1, th.lo & 1 ? 5 : 0,

ret >> 1, ret & 1 ? 5 : 0,

fan_state[netwinder_get_fan()]);

return0;

}

staticvoid__exit ds1620_exit(void)

{

移除/proc节点

#ifdefTHERM_USE_PROC

remove_proc_entry("therm",NULL);

#endif

注销混杂设备。

misc_deregister(&ds1620_miscdev);

}

再来看一下混杂设备的结构体及接口函数：

structmiscdevice {

intminor;

constchar*name;

conststructfile_operations*fops;

structlist_headlist;

structdevice*parent;