3、实现步骤
ADC设备在Linux中可以看做是简单的字符设备，也可以当做是一混杂设备(misc设备)，这里我们就看做是misc设备来实现ADC的驱动。注意：这里我们获取AD转换后的数据将采用中断的方式，即当AD转换完成后产生AD中断，在中断服务程序中来读取ADCDAT0的第0-9位的值(即AD转换后的值)。
#include <linux/errno.h>#include <linux/kernel.h>//printk()#include <linux/module.h>#include <linux/slab.h>#include <linux/input.h>#include <linux/init.h>#include <linux/serio.h>#include <linux/delay.h>#include <linux/clk.h>#include <linux/wait.h>#include <linux/sched.h>//包含很多驱动使用的内核API的定义。睡眠函数，变量声明#include <asm/io.h>//定义IO映射#include <asm/irq.h>#include <asm/uaccess.h>#include <mach/regs-clock.h>#include <plat/regs-timer.h>#include <plat/regs-adc.h>//ADC寄存器的定义#include <mach/regs-gpio.h>#include <linux/cdev.h>#include <linux/miscdevice.h>#include "s3c24xx-adc.h"#undef DEBUG//#define DEBUG#ifdef DEBUG#define DPRINTK(x…) {printk(__FUNCTION__"(%d): ",__LINE__);printk(##x);}#else#define DPRINTK(x…) (void)(0)#endif#define DEVICE_NAME "Myadc"//经过虚拟地址映射之后的内存地址static void __iomem *base_addr; typedef struct {wait_queue_head_t wait;//阻塞 等待队列，进程读取设备，如果没有转换数据，就会睡眠在此队列上int channel;//AD转换通道 s3c2440有八通道的ad，但是只有四个通道AIN[3:0]可以使用，其他四个用于触摸屏int prescale;//预分频值 计算转换速率的时候使用}ADC_DEV;//申请并初始化信号量DECLARE_MUTEX(ADC_LOCK); //ADC驱动是否拥有AD转换器资源的状态变量static int OwnADC = 0; static ADC_DEV adcdev; //adcdevstatic volatile int ev_adc = 0;//标识AD转换后的数据是否可以读取，0表示不可读取static int adc_data;//保存读取后的AD转换的值，该值在ADC中断中读取//保存从时钟平台队列中获取ADC的时钟static struct clk *adc_clock; //定义ADC的寄存器#define ADCCON(*(volatile unsigned long *)(base_addr + S3C2410_ADCCON))//ADC control#define ADCTSC(*(volatile unsigned long *)(base_addr + S3C2410_ADCTSC))//ADC touch screen control#define ADCDLY(*(volatile unsigned long *)(base_addr + S3C2410_ADCDLY))//ADC start or Interval Delay#define ADCDAT0(*(volatile unsigned long *)(base_addr + S3C2410_ADCDAT0))//ADC conversion data 0#define ADCDAT1(*(volatile unsigned long *)(base_addr + S3C2410_ADCDAT1))//ADC conversion data 1#define ADCUPDN(*(volatile unsigned long *)(base_addr + 0x14))//Stylus Up/Down interrupt status//以下都定义于ADCCON中#define PRESCALE_DIS(0 << 14)//预分频禁止#define PRESCALE_EN(1 << 14)//预分频允许#define PRSCVL(x)((x) << 6)//预分频值设置#define ADC_INPUT(x)((x) << 3)//模拟输入通道选择 SEL_MUX#define ADC_START(1 << 0)//开始AD转换#define ADC_ENDCVT(1 << 15)//AD转换结束 ECFLG//设置ADC控制器，开启ADC转换#define START_ADC_AIN(ch, prescale) \do{ \ADCCON = PRESCALE_EN | PRSCVL(prescale) | ADC_INPUT((ch)) ; \ADCCON |= ADC_START; \}while(0)//中断服务程序，从ADC数据寄存器中读取AD转换后的值static irqreturn_t adcdone_int_handler(int irq, void *dev_id){if (OwnADC) { //如果ADC驱动拥有AD转换器资源，则从ADC寄存器读取转换状态adc_data = ADCDAT0 & 0x3ff;//AD转换后的值保存在[0~9]位?ev_adc = 1;//将可读标识为1，并唤醒等待队列wake_up_interruptible(&adcdev.wait);}return IRQ_HANDLED;}static ssize_t s3c2410_adc_read(struct file *filp, char *buffer, size_t count, loff_t *ppos){char str[20];int value;size_t len;if (down_trylock(&ADC_LOCK) == 0) {//尝试获取信号量，判断AD转换器资源是否可用OwnADC = 1;//标记AD转换器资源可用START_ADC_AIN(adcdev.channel, adcdev.prescale);//设置ADC控制器，开启AD转换wait_event_interruptible(adcdev.wait, ev_adc);//使等待队列进入唤醒，等待转换结束ev_adc = 0;//已经有AD转换后的数据，则标识清0，给下一次读作判断DPRINTK("AIN[%d] = 0x%04x, %d\n", adcdev.channel, adc_data, ADCCON & 0x80 ? 1:0);value = adc_data;//把转换结果赋值，以便传递给应用层OwnADC = 0;//释放转换器资源up(&ADC_LOCK);//解锁} else {//没有AD转换器资源value = -1;}len = sprintf(str, "%d\n", value);if (count >= len) {int r = copy_to_user(buffer, str, len);//将读取到的ADC转换后的值发往到应用程序return r ? r : len;} else {return -EINVAL;}}//打开ADC，并设置频道和预分频值static int s3c2410_adc_open(struct inode *inode, struct file *filp){init_waitqueue_head(&(adcdev.wait));//初始化中断队列adcdev.channel=0;//设置ADC频道adcdev.prescale=0xff;//设置预分频值DPRINTK( "adc opened\n");return 0;}static int s3c2410_adc_release(struct inode *inode, struct file *filp){DPRINTK( "adc closed\n");return 0;}//非标准C的用法，GNU C的用法static struct file_operations dev_fops = {owner: THIS_MODULE,open: s3c2410_adc_open,read: s3c2410_adc_read,release: s3c2410_adc_release,};static struct miscdevice misc = {.minor = MISC_DYNAMIC_MINOR,.name = DEVICE_NAME,.fops = &dev_fops,};//初始化设备static int __init dev_init(void){int ret;//将ADC的IO端口占用的这段I/O空间映射到内存的虚拟地址，，//S3C2410_PA_ADC是ADC控制器的基地址，0x20是虚拟地址长度base_addr=ioremap(S3C2410_PA_ADC,0x20);if (base_addr == NULL) {printk(KERN_ERR "Failed to remap register block\n");return -ENOMEM;}//获取ADC时钟adc_clock = clk_get(NULL, "adc");if (!adc_clock) {printk(KERN_ERR "failed to get adc clock source\n");return -ENOENT;}clk_enable(adc_clock);//时钟使能/* normal ADC */ADCTSC = 0;//ADC中断申请，采用共享中断，ret = request_irq(IRQ_ADC, adcdone_int_handler, IRQF_SHARED, DEVICE_NAME, &adcdev); //IRQF_SHARED 共享中断的if (ret) {iounmap(base_addr);//解除内存映射return ret;}ret = misc_register(&misc);printk (DEVICE_NAME"\tinitialized\n");return ret;}static void __exit dev_exit(void){free_irq(IRQ_ADC, &adcdev);//释放中断iounmap(base_addr);//解除内存映射//屏蔽和销毁时钟if (adc_clock) {clk_disable(adc_clock);clk_put(adc_clock);adc_clock = NULL;}misc_deregister(&misc);}//导出信号量ADC_LOCK在触摸屏驱动中使用，因为触摸屏和ADC公用寄存器，会产生竞争//用信号量保证资源的互斥访问EXPORT_SYMBOL(ADC_LOCK); module_init(dev_init);module_exit(dev_exit);MODULE_LICENSE("GPL");MODULE_AUTHOR("FriendlyARM Inc.");4、测试程序#include <stdio.h>#include <stdlib.h>#include <errno.h>int main(int argc, char **argv){int fd;//以阻塞方式打开设备文件，非阻塞时flags=O_NONBLOCKfd = open("/dev/Myadc", 0);if(fd < 0){printf("Open ADC Device Faild!\n");exit(1);}while(1){int ret;int data;ret = read(fd, &data, sizeof(data));//读设备if(ret != sizeof(data)){if(errno != EAGAIN){printf("Read ADC Device Faild!\n");}continue;}else{printf("Read ADC value is: %d\n", data);}}close(fd);return 0;}
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