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DS18B20 驱动编写
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嵌入式開發(fā)平臺：mini2440
DS18B20 所用GPIO：S3C2410_GPF(3)
一、DS18B20 時(shí)序分析
? ? ? ? DS18B20的一線工作協(xié)議流程是：初始化→ROM操作指令→存儲器操作指令→數(shù)據(jù)傳輸，其工作時(shí)序包括：初始化時(shí)序、寫時(shí)序、讀時(shí)序。
1、初始化時(shí)序
? ? ? ?主機(jī)首先發(fā)出一個(gè)480-960微秒的低電平脈沖，然后釋放總線變?yōu)楦唠娖?#xff0c;并在隨后的480微秒時(shí)間內(nèi)對總線進(jìn)行檢測，如果有低電平出現(xiàn)說明總線上有器件已做出應(yīng)答 ，若無低電平出現(xiàn)一直都是高電平說明總線上無器件應(yīng)答。
?作為從器件的DS18B20在一上電后就一直在檢測總線上是否有480-960微秒的低電平出現(xiàn)，如果有，在總線轉(zhuǎn)為高電平后等待15-60微秒后將總線電平拉低60-240微秒做出響應(yīng)存在脈沖，告訴主機(jī)本器件已做好準(zhǔn)備 ，若沒有檢測到就一直在檢測等待。
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static ? int ?ds18b20_init( void )???? {???? ????int ?retval?=?0;???? ???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?0);???? ???? ????s3c2410_gpio_setpin(DQ,?1);???? ????udelay(2);???? ????s3c2410_gpio_setpin(DQ,?0);??? ????udelay(500);?????????????????? ???? ????s3c2410_gpio_setpin(DQ,?1);??? ????udelay(60);???? ???? ?????? ????s3c2410_gpio_cfgpin(DQ,?CFG_IN);???? ????retval?=?s3c2410_gpio_getpin(DQ);???? ???? ????udelay(500);???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?0);???? ????s3c2410_gpio_setpin(DQ,?1);??? ???? ????return ?retval;???? }????
2、寫時(shí)序
? ? ?寫周期最少為60微秒 ，最長不超過120微秒，寫周期一開始作為主機(jī)先把總線拉低1微秒表示寫周期開始 ，隨后若主機(jī)想寫0，則繼續(xù)拉低電平最少60微秒 直至寫周期結(jié)束，然后釋放總線為高電平；若主機(jī)想寫1，在一開始拉低總線電平1微秒后就釋放總線為高電平，一直到寫周期結(jié)束 。
? ? ?而作為從機(jī)的DS18B20則在檢測到總線被拉低后等待15微秒然后從15μs到45μs開始對總線采樣，在采樣期內(nèi)總線為高電平則為1，若采樣期內(nèi)總線為低電平則為0。
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static ? void ?write_byte(unsigned? char ?data)???? {???? ????int ?i?=?0;???? ???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?1);???? ???? ????for ?(i?=?0;?i?<?8;?i++)???? ????{???? ?????????? ????????s3c2410_gpio_setpin(DQ,?1);???? ????????udelay(2);???? ????????s3c2410_gpio_setpin(DQ,?0);???? ????????s3c2410_gpio_setpin(DQ,?data?&?0x01);???? ????????udelay(60);???? ????????data?>>=?1;???? ????}???? ????s3c2410_gpio_setpin(DQ,?1);??? }????
3、讀時(shí)序
? ? ? 對于讀數(shù)據(jù)操作時(shí)序也分為讀0時(shí)序和讀1時(shí)序兩個(gè)過程，讀時(shí)序是從主機(jī)把單總線拉低之后，在1微秒之后就得釋放單總線為高電平 ，以讓DS18B20把數(shù)據(jù)傳輸?shù)絾慰偩€上。DS18B20在檢測到總線被拉低1微秒后，便開始送出數(shù)據(jù)，若是要送出0就把總線拉為低電平直到讀周期結(jié)束；若要送出1則釋放總線為高電平。
? ? ?主機(jī)在一開始拉低總線1微秒后釋放總線，然后在包括前面的拉低總線電平1微秒在內(nèi)的15微秒時(shí)間內(nèi)完成對總線進(jìn)行采樣檢測，采樣期內(nèi)總線為低電平則確認(rèn)為0，采樣期內(nèi)總線為高電平則確認(rèn)為1，完成一個(gè)讀時(shí)序過程，至少需要60μs才能完成。
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static ?unsigned? char ?read_byte( void )???? {???? ????int ?i;???? ????unsigned?char ?data?=?0;???? ???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?0);??? ??? ????for ?(i?=?0;?i?<?8;?i++)???? ????{???? ?????????? ????????s3c2410_gpio_setpin(DQ,?1);???? ????????udelay(2);???? ????????s3c2410_gpio_setpin(DQ,?0);???? ????????udelay(2);???? ????????s3c2410_gpio_setpin(DQ,?1);???? ????????udelay(8);???? ????????data?>>=?1;???? ????????s3c2410_gpio_cfgpin(DQ,?CFG_IN);???? ????????if ?(s3c2410_gpio_getpin(DQ))???? ????????????data?|=?0x80;???? ????????udelay(50);???? ????}???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?0);???? ????s3c2410_gpio_setpin(DQ,?1);??? ????return ?data;???? }????
二、操作方法
? ? ? ?DS18B20單線通信功能是分時(shí)完成的，有嚴(yán)格的時(shí)序概念，如果出現(xiàn)序列混亂，1-WIRE器件將不影響主機(jī)，因此讀寫時(shí)序很重要。系統(tǒng)對DS18B20的各種操作必須按協(xié)議進(jìn)行，根據(jù)DS18B20的協(xié)議規(guī)定，微控制器控制DS18B20完成溫度的轉(zhuǎn)換必須經(jīng)過以下4個(gè)步驟：
1）每次讀寫前對DS18B20進(jìn)行復(fù)位初始化 。復(fù)位要求主CPU將數(shù)據(jù)線下拉500μs，然后釋放，DS18B20收到信號后等待16μs-60μs左右，然后發(fā)出60μs-240μs的存在低脈沖，主CPU收到此信號后表示復(fù)位成功。
2）發(fā)送一條ROM指令
3）發(fā)送存儲器指令
1、讓DS18B20進(jìn)行一次溫度轉(zhuǎn)換的具體操作如下：
a -- 主機(jī)先做個(gè)復(fù)位操作；
2、讀取RAM的溫度數(shù)據(jù)，同樣，這個(gè)操作也要按照三個(gè)步驟：
a -- 主機(jī)發(fā)出復(fù)位操作并接受DS18B20的應(yīng)答（存在）脈沖；
三、具體驅(qū)動編寫
1、ds18b20_drv.c
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#include?<linux/init.h>??? ?? #include?<linux/module.h>??? ?? #include?<linux/delay.h>??? ?? #include?<linux/kernel.h>??? ?? #include?<linux/moduleparam.h>??? ?? #include?<linux/init.h>??? ?? #include?<linux/types.h>??? ?? #include?<linux/fs.h>??? ?? #include?<mach/regs-gpio.h>??? ?? #include?<mach/hardware.h>??? ?? #include?<linux/cdev.h>??? ?? #include?<asm/uaccess.h>??? ?? #include?<linux/errno.h>??? ?? #include?<linux/gpio.h>??? ?? #include?<linux/device.h>??? ?? ???? ???? #define?DQ?????????S3C2410_GPF(3)??? ?? #define?CFG_IN?????S3C2410_GPIO_INPUT??? ?? #define?CFG_OUT????S3C2410_GPIO_OUTPUT??? ?? ???? ?? static ? int ?ds18b20_major?=?0;???? static ? int ?ds18b20_minor?=?0;???? static ? int ?ds18b20_nr_devs?=?1;???? ???? ?? static ? struct ?ds18b20_device???? {???? ????struct ?cdev?cdev;???? };???? ???? struct ?ds18b20_device?*ds18b20_devp;???? ???? ???? static ? struct ? class ?*ds18b20_class;???? static ? struct ?class_device?*ds18b20_class_dev;???? ???? ???? static ? int ?ds18b20_open( struct ?inode?*inode,? struct ?file?*filp);???? static ? int ?ds18b20_init( void );???? static ? void ?write_byte(unsigned? char ?data);???? static ?unsigned? char ?read_byte( void );???? static ?ssize_t?ds18b20_read( struct ?file?*filp,? char ?__user?*?buf,? size_t ?count,?loff_t?*?f_pos);???? void ?ds18b20_setup_cdev( struct ?ds18b20_device?*dev,? int ?index);???? ???? static ? int ?ds18b20_open( struct ?inode?*inode,? struct ?file?*filp)???? {???? ????int ?flag?=?0;???? ???? ????flag?=?ds18b20_init();???? ????if ?(flag?&?0x01)???? ????{???? ????????printk(KERN_WARNING?"open?ds18b20?failed\n" );???? ????????return ?-1;???? ????}???? ????printk(KERN_NOTICE?"open?ds18b20?successful\n" );???? ????return ?0;???? }???? ???? static ? int ?ds18b20_init( void )???? {???? ????int ?retval?=?0;???? ???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?0);???? ???? ????s3c2410_gpio_setpin(DQ,?1);???? ????udelay(2);???? ????s3c2410_gpio_setpin(DQ,?0);??? ????udelay(500);?????????????????? ???? ????s3c2410_gpio_setpin(DQ,?1);??? ????udelay(60);???? ???? ?????? ????s3c2410_gpio_cfgpin(DQ,?CFG_IN);???? ????retval?=?s3c2410_gpio_getpin(DQ);???? ???? ????udelay(500);???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?0);???? ????s3c2410_gpio_setpin(DQ,?1);??? ???? ????return ?retval;???? }???? ???? static ? void ?write_byte(unsigned? char ?data)???? {???? ????int ?i?=?0;???? ???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?1);???? ???? ????for ?(i?=?0;?i?<?8;?i++)???? ????{???? ?????????? ????????s3c2410_gpio_setpin(DQ,?1);???? ????????udelay(2);???? ????????s3c2410_gpio_setpin(DQ,?0);???? ????????s3c2410_gpio_setpin(DQ,?data?&?0x01);???? ????????udelay(60);???? ????????data?>>=?1;???? ????}???? ????s3c2410_gpio_setpin(DQ,?1);??? }???? ???? static ?unsigned? char ?read_byte( void )???? {???? ????int ?i;???? ????unsigned?char ?data?=?0;???? ???? ????for ?(i?=?0;?i?<?8;?i++)???? ????{???? ?????????? ????????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????????s3c2410_gpio_pullup(DQ,?0);???? ????????s3c2410_gpio_setpin(DQ,?1);???? ????????udelay(2);???? ????????s3c2410_gpio_setpin(DQ,?0);???? ????????udelay(2);???? ????????s3c2410_gpio_setpin(DQ,?1);???? ????????udelay(8);???? ????????data?>>=?1;???? ????????s3c2410_gpio_cfgpin(DQ,?CFG_IN);???? ????????if ?(s3c2410_gpio_getpin(DQ))???? ????????????data?|=?0x80;???? ????????udelay(50);???? ????}???? ????s3c2410_gpio_cfgpin(DQ,?CFG_OUT);???? ????s3c2410_gpio_pullup(DQ,?0);???? ????s3c2410_gpio_setpin(DQ,?1);??? ????return ?data;???? }???? ???? static ?ssize_t?ds18b20_read( struct ?file?*filp,? char ?__user?*?buf,? size_t ?count,?loff_t?*?f_pos)???? {???? ????int ?flag;???? ????unsigned?long ?err;???? ????unsigned?char ?result[2]?=?{?0x00,?0x00?};???? ?????? ???? ????flag?=?ds18b20_init();???? ????if ?(flag?&?0x01)???? ????{???? ????????printk(KERN_WARNING?"ds18b20?init?failed\n" );???? ????????return ?-1;???? ????}???? ???? ????write_byte(0xcc);???? ????write_byte(0x44);???? ???? ????flag?=?ds18b20_init();???? ????if ?(flag?&?0x01)???? ????????return ?-1;???? ???? ????write_byte(0xcc);???? ????write_byte(0xbe);???? ???? ????result[0]?=?read_byte();?????? ????result[1]?=?read_byte();?????? ???? ????err?=?copy_to_user(buf,?&result,?sizeof (result));???? ????return ?err???-EFAULT?:?min( sizeof (result),?count);???? }???? ???? static ? struct ?file_operations?ds18b20_dev_fops?=?{???? ????.owner?=?THIS_MODULE,???? ????.open?=?ds18b20_open,???? ????.read?=?ds18b20_read,???? };???? ???? void ?ds18b20_setup_cdev( struct ?ds18b20_device?*dev,? int ?index)???? {???? ????int ?err,?devno?=?MKDEV(ds18b20_major,?ds18b20_minor?+?index);???? ???? ????cdev_init(&dev->cdev,?&ds18b20_dev_fops);???? ????dev->cdev.owner?=?THIS_MODULE;???? ????err?=?cdev_add(&(dev->cdev),?devno,?1);???? ????if ?(err)???? ????{???? ????????printk(KERN_NOTICE?"ERROR?%d?add?ds18b20\n" ,?err);???? ????}???? }???? ???? static ? int ?__init?ds18b20_dev_init( void )???? {???? ????int ?result;???? ????dev_t?dev?=?0;???? ???? ????dev?=?MKDEV(ds18b20_major,?ds18b20_minor);???? ???? ????if ?(ds18b20_major)???? ????{???? ????????result?=?register_chrdev_region(dev,?ds18b20_nr_devs,?"ds18b20" );???? ????}???? ????else ???? ????{???? ????????result?=?alloc_chrdev_region(&dev,?ds18b20_minor,?ds18b20_nr_devs,?"ds18b20" );???? ????????ds18b20_major?=?MAJOR(dev);???? ????}???? ????if ?(result?<?0)???? ????{???? ????????printk(KERN_WARNING?"ds18b20:?failed?to?get?major\n" );???? ????????return ?result;???? ????}???? ???? ???????? ????ds18b20_devp?=?kmalloc(sizeof ( struct ?ds18b20_device),?GFP_KERNEL);???? ????if ?(!ds18b20_devp)???? ????{??????????????????????????????? ????????result?=?-ENOMEM;???? ????????goto ?fail_malloc;???? ????}???? ????memset(ds18b20_devp,?0,?sizeof ( struct ?ds18b20_device));???? ???? ????ds18b20_setup_cdev(ds18b20_devp,?0);???? ???? ???????? ????ds18b20_class?=?class_create(THIS_MODULE,?"ds18b20_sys_class" );???? ????if ?(IS_ERR(ds18b20_class))???? ????????return ?PTR_ERR(ds18b20_class);???? ???? ????ds18b20_class_dev?=???? ????????device_create(ds18b20_class,?NULL,?MKDEV(ds18b20_major,?0),?NULL,?"ds18b20" );???? ????if ?(unlikely(IS_ERR(ds18b20_class_dev)))???? ????????return ?PTR_ERR(ds18b20_class_dev);???? ???? ????return ?0;???? ???? ??fail_malloc:???? ????unregister_chrdev_region(dev,?1);???? ????return ?result;???? }???? ???? static ? void ?__exit?ds18b20_dev_exit( void )???? {???? ????cdev_del(&ds18b20_devp->cdev);?????? ????kfree(ds18b20_devp);???????????? ????unregister_chrdev_region(MKDEV(ds18b20_major,?0),?ds18b20_nr_devs);????? ????device_unregister(ds18b20_class_dev);???? ????class_destroy(ds18b20_class);???? }???? ???? module_init(ds18b20_dev_init);???? module_exit(ds18b20_dev_exit);???? MODULE_LICENSE("Dual?BSD/GPL" );????
2、app-ds18b20.c
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#include?<stdio.h>??? ?? #include?<stdlib.h>??? ?? #include?<unistd.h>??? ?? #include?<linux/ioctl.h>??? ?? ???? ?? void ?ds18b20_delay( int ?i);???? ???? int ?main()???? {???? ????int ?fd,?i;???? ????unsigned?char ?result[2];???? ?? ????unsigned?char ?integer_value?=?0;???? ????float ?decimal_value?=?0;???? ?? ????float ?temperature?=?0;???? ???? ????fd?=?open("/dev/ds18b20" ,?0);???? ????if ?(fd?<?0)???? ????{???? ????????perror("open?device?failed\n" );???? ????????exit(1);???? ????}???? ????while ?(1)???? ????{???? ????????i++;???? ????????read(fd,?&result,?sizeof (result));???? ????????integer_value?=?((result[0]?&?0xf0)?>>?4)?|?((result[1]?&?0x07)?<<?4);???? ?????????? ????????decimal_value?=?0.5?*?((result[0]?&?0x0f)?>>?3)?+?0.25?*?((result[0]?&?0x07)?>>?2);???? ????????temperature?=?(float )integer_value?+?decimal_value;???? ????????printf("Current?Temperature:%6.2f\n" ,?temperature);???? ???? ????????ds18b20_delay(500);???? ????}???? }???? ???? void ?ds18b20_delay( int ?i)???? {???? ????int ?j,?k;???? ????for ?(j?=?0;?j?<?i;?j++)???? ????????for ?(k?=?0;?k?<?50000;?k++)?;???? }????
測試結(jié)果：
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[root@www.linuxidc.com?home]#???? [root@www.linuxidc.com?home]#./app-ds18b20???? open?ds18b20?successful???? Current?Temperature:?23.50???? Current?Temperature:?23.50???? Current?Temperature:?23.25???? Current?Temperature:?23.50???? Current?Temperature:?23.50???? Current?Temperature:?23.50???? ^C???? [root@www.linuxidc.com?home]# ? ?
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