嵌入式系统设计与开发教程 课件 第5章 基于Linux的驱动程序设计-2

编写PWM驱动以及测试程序开发板的BEEP灯电路在Exynos4412中，一共有5个32位定时器，这些定时器课发送中断信号给ARM处理器，另外，定时器0、1、2、3包含了脉冲宽度调制（PWM），并可驱动其对应的I/O引脚。每个定时器都有一个独立的32位递减计数器，定时器启动后，计数缓冲寄存器（TCNTBn）将初始值加载到递减计数器，定时器时钟驱动递减计数器，当递减计数器达到零，自动产生计时器中断请求，同时相应TCNTBn的值自动重新加载，开始下一个循环。但是，如果定时器停止，如清除TCONn的定时器使能位，TCNTBn的值将不会重新加载到计数器中。每个定时器都有一个独立的32位比较缓冲寄存器（TCMPBn）。当递减计数器与定时器控制逻辑中比较寄存器的值相匹配时，PWM输出会产生由低到高的电平跳变，因此，比较寄存器决定PWM输出的开启时间或关闭时间。1、初始化定时器n对应的计数缓冲寄存器TCNTBn为159，定时器n对应的计数比较缓冲寄存器TCMPBn为109。2、启动定时器n：设置定时器n的启动位为1，并手动更新为为零。此时寄存器TCNTBn的值159自动加载到内部的递减寄存器中，并开始递减计数，同时输出引脚TOUTn输出低电平。3、当递减寄存器的值递减到109（TCMPBn的数值）时，定时器n对应的电平输出引脚TOUTn从低电平翻转到高电平。4、当递减寄存器的值递减到0时，计数缓冲寄存器TCNTBn的值159重新被加载到定时器的递减器，定时器n对应的电平输出引脚TOUTn重新输出低电平，这样流程重复进行，引脚TOUTn就输出占空比可控的PWM波。值得注意的是，修改计数缓冲寄存器TCNTBn或比较缓冲寄存器TCMPBn的值，只能在下一个PWM周期起作用，不影响当前周期PWM的占空比。PWM驱动源程序文件（pwm_dev.c）设计，关键步骤为：pwm_dev_open：主要实现对PWM的寄存器进行初始化工作，pwm_dev_release：主要实现停止PWM波形的输出，pwm_dev_ioctl：分别设置了四个命令实现PWM的启动，停止，设置分频系数以及设置频率。在驱动加载时，即pwm_dev_init函数中，将实例化的文件操作结构体pwm_ops与设备号关联并注册到内核中，同时生成对应的设备文件。#include<linux/module.h>#include<linux/kernel.h>#include<linux/init.h>#include<linux/platform_device.h>#include<linux/fb.h>#include<linux/err.h>#include<linux/slab.h>#include<linux/delay.h>#include<linux/gpio.h>#include<mach/gpio.h>#include<plat/gpio-cfg.h>

MODULE_LICENSE("GPLv2");

#defineDEVICE_NAME "pwm"//定义设备的名字为

pwm#defineDEVICE_NUM 1staticintmajor=0;//主设备号，次设备号staticintminor=0;

structcdevpwm_dev_cdev;staticstructclass*pwm_class;

pwm_dev.c

#defineNS_IN_1HZ 0x6400//100MHz/256/16

#defineBUZZER_PMW_GPIO EXYNOS4_GPD0(0)//蜂鸣器GPIO配置

#defineTIMER_BASE 0X139D0000void__iomem *timer_base;#defineTCFG0 (void__iomem *)(timer_base+0X00)#defineTCFG1 (void__iomem *)(timer_base+0X04)#defineTCON (void__iomem *)(timer_base+0X08)#defineTCNTB1 (void__iomem *)(timer_base+0X0C)#defineTCMPB1 (void__iomem *)(timer_base+0X10)

#definePWM_ON _IO('K',0)#definePWM_OFF _IO('K',1)#definePWM_SET_PRE _IOW('K',2,int)#definePWM_SET_FREQ _IOW('K',3,int)//open方法函数，主要打开pwm的操作staticintpwm_dev_open(structinode*inode,structfile*file){ printk(KERN_INFO"pwm_openstart"); s3c_gpio_cfgpin(BUZZER_PMW_GPIO,S3C_GPIO_SFN(2));

writel(readl(TCFG0)|0xff,TCFG0); writel((readl(TCFG1)&(~0x0f))|0x04,TCFG1); writel(300,TCNTB1); writel(150,TCMPB1); writel((readl(TCON)&(~0x1f))|0X02,TCON); return0;}//close方法函数，主要是关闭pwm操作staticintpwm_dev_release(structinode*inode,structfile*file){ printk(KERN_INFO"pwm_close"); writel(readl(TCON)&(~0x1f),TCON); s3c_gpio_cfgpin(BUZZER_PMW_GPIO,S3C_GPIO_OUTPUT); return0;}//控制io口方法函数staticlongpwm_dev_ioctl(structfile*filep,unsignedintcmd,unsignedlongarg){ intdata=arg;

if(_IOC_TYPE(cmd)!='K') return-ENOTTY; if(_IOC_NR(cmd)>3) return-ENOTTY;

printk(KERN_INFO"pwm_ioctlstart");

switch(cmd){ casePWM_ON: writel((readl(TCON)&(~0x1f))|0X0D,TCON); break; casePWM_SET_PRE: if(data==0) return-EINVAL; writel(readl(TCON)&(~0x1f),TCON); writel((readl(TCFG0)&(~0xff))|(data&0xff),TCFG0); writel((readl(TCON)&(~0x1f))|0X0D,TCON); break; casePWM_SET_FREQ: if(data==0) return-EINVAL;data=(NS_IN_1HZ)/data; writel(data,TCNTB1); writel(data>>1,TCMPB1); break; casePWM_OFF: writel(readl(TCON)&(~0x1f),TCON); break; } return0;}//operations结构体staticstructfile_operationspwm_ops={ .owner=THIS_MODULE, .unlocked_ioctl=pwm_dev_ioctl, .open=pwm_dev_open, .release=pwm_dev_release};

//pwm设备初始化,设备在被insmod插入模块到内核的过程中会调用这个函数staticint__initpwm_dev_init(void){ intret=0; dev_tdevno; printk(KERN_INFO"pwm_dev_initstart");

gpio_free(BUZZER_PMW_GPIO); ret=gpio_request(BUZZER_PMW_GPIO,DEVICE_NAME);

if(ret){ printk(KERN_INFO"requestGPIO%dforpwmfailed\n",BUZZER_PMW_GPIO); gotoERR1; } s3c_gpio_cfgpin(BUZZER_PMW_GPIO,S3C_GPIO_OUTPUT); gpio_set_value(BUZZER_PMW_GPIO,0);/*动态注册设备号*/ ret=alloc_chrdev_region(&devno,minor,DEVICE_NUM,"pwmdriver"); /*获得主设备号*/ major=MAJOR(devno); printk(KERN_INFO"dynamicadev_regionmajoris%d!\n",major); if(ret<0){ printk(KERN_INFO"register_chrdev_regionreq%disfailed!\n",major); gotoERR2;}else{ cdev_init(&pwm_dev_cdev,&pwm_ops); pwm_dev_cdev.owner=THIS_MODULE; ret=cdev_add(&pwm_dev_cdev,devno,DEVICE_NUM); if(ret<0){ printk(KERN_INFO"cdev_add%disfailed!\n",ret); gotoERR3; } else{ pwm_class=class_create(THIS_MODULE,DEVICE_NAME); device_create(pwm_class,NULL,devno,NULL,DEVICE_NAME); }}//地址映射timer_base=ioremap(TIMER_BASE,0x20);if(timer_base==NULL){ printk(KERN_INFO"ioremapfailed!\n"); ret=-ENOMEM; gotoERR4;} printk(KERN_INFODEVICE_NAME"\tinitialized\n");return0;

ERR4: device_destroy(pwm_class,devno); class_unregister(pwm_class); class_destroy(pwm_class); cdev_del(&pwm_dev_cdev);ERR3: unregister_chrdev_region(devno,DEVICE_NUM);ERR2: gpio_free(BUZZER_PMW_GPIO);ERR1: returnret;}

//设备在被卸载rmmod的过程中会调用这个函数staticvoid__exitpwm_dev_exit(void){ dev_tdevno=MKDEV(major,minor);

printk("pwm_exitstart");

gpio_free(BUZZER_PMW_GPIO); device_destroy(pwm_class,devno); class_unregister(pwm_class); class_destroy(pwm_class); cdev_del(&pwm_dev_cdev); unregister_chrdev_region(devno,DEVICE_NUM); iounmap(timer_base); printk(KERN_INFO"pwm_dev_exit!\n"); return;}

//模块初始化module_init(pwm_dev_init);//销毁模块module_exit(pwm_dev_exit);Makefileobj-m=pwm_dev.oKERNELDIR:=/root/yizhi/boot-kernel-source/iTop4412_Kernel_3.0PWD:=$(shellpwd)modules: $(MAKE)-C$(KERNELDIR)M=$(PWD)modulesclean: rm-rf*.o~core.depend*.ko*.mod.c*.*.cmd rm–rf.tmp_versions要编译的结果，名字和驱动源程序相同在PWM测试应用程序中，根据PWM驱动设计的3个文件操作open、close、ioctl，操作对应的PWM设备驱动文件/dev/pwm，来实现对PWM的控制。本例中，通过PWM驱动设置不同音调的频率，以及设置不同频率的播放时间，实现控制蜂鸣器输出音乐旋律。/*pwm_music.c*/#include<stdio.h>#include<stdlib.h>#include<unistd.h>#include<fcntl.h>#include<string.h>#include<sys/types.h>#include<sys/stat.h>#include<sys/ioctl.h>#include"pwm_music.h“intmain(){inti=0;intdev_fd;intpre=255;arm-none-linux-gnueabi-gcc–opwm_musicpwm_music.cdev_fd=open("/dev/pwm",O_RDWR|O_NONBLOCK);if(dev_fd<0){printf("error!\n");return-1;}ioctl(dev_fd,PWM_ON);ioctl(dev_fd,PWM_SET_PRE,pre);for(i=0;i<sizeof(Twotigers)/sizeof(Note);i++){ ioctl(dev_fd,PWM_SET_FREQ,Twotigers[i].pitch); usleep(Twotigers[i].dimation*50);}ioctl(dev_fd,PWM_OFF);close(dev_fd);return0;}打开pwm设置基本频率播放音调音调的持续时间停止pwm/*pwm_music.h*/#ifnd