图1  ADC Functional Block Diagram

      2. Exynos4412 A/D 控制器寄存器
      1）A/D控制寄存器ADCCON

      2）A/D数据寄存器

      3）A/D通道Mux寄存器

      三、A/D转换器实例
      1. 电路连接如下：
      利用一个电位计输出电压到4412的AIN3管脚。输入的电压范围为0~1.8V。

1. 代码如下：
#include <asm/ioctl.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/uaccess.h>
#include <asm/io.h>
 
#define ADC_MAGIC  'A'
#define CMD_ONE       1
#define ADC_CMD_GET _IOR(ADC_MAGIC, CMD_ONE, int)
 
//寄存器定义
#define        ADC_CFG            (0x10010118)
#define           ADCCON              (0x126C0000)
#define           ADCDAT              (0x126C000C)
#define           ADCMUX             (0x126C001C)
 
dev_t dev;
int minor_base = 0;
int adc_count = 1;
char adc_name[] = "adc";
struct cdev *pcdev = NULL;
struct class *pcls = NULL;
static unsigned int *adccfg;
static unsigned int *adcmux;
static unsigned int *adccon;
static unsigned int *adcdat;
 
int AdcInit(void)
{
       int ret = 0;
      
       adccfg = ioremap(ADC_CFG, 4);
       if (adccfg == NULL) {
              printk("ioremap adccfg\n");
              ret = -ENOMEM;
              return ret;
       }
 
       adcmux = ioremap(ADCMUX, 4);
       if (adcmux == NULL) {
              printk("ioremap adcmux\n");
              ret = -ENOMEM;
              goto ERR1;
       }
 
       adccon = ioremap(ADCCON, 4);
       if (adccon == NULL) {
              printk("ioremap adccon\n");
              ret = -ENOMEM;
              goto ERR2;
       }
 
       adcdat = ioremap(ADCDAT, 4);
       if (adcdat == NULL) {
              printk("ioremap adcdat\n");
              ret = -ENOMEM;
              goto ERR3;
       }
      
       //ADC_CFG &= ~(0x1 << 16);
       writel(readl(adccfg) & ~(0x1<<16), adccfg);  //Bit_16:Select ADC Mux 0:General ADC, 1:MTCADC
      
       //ADCMUX = 0x3;
       writel(3, adcmux);  //0x3: 0011 = AIN3   //原理图管脚查到XadcAIN3
 
       //12bit A/D conversion; enable A/D converter prescaler; prescaler value:20; A/D conversion start by read
       //ADCCON = (0x1<<16) | (0x1<<14) | (19<<6) | 0x1<<1;
       //ADCDAT & 0xfff;
      
       writel((0x1<<16) | (0x1<<14) | (19<<6) | 0x1<<1, adccon);
      
       return 0;
      
ERR3:
       iounmap(adccon);
ERR2:
       iounmap(adcmux);
ERR1:
       iounmap(adccfg);
       return ret;
}
 
unsigned int adc_get(void)
{
       unsigned int adc_value;
       unsigned int temp_value;
      
       readl(adcdat);
       while(!(readl(adccon) & (0x1<<15)));
       adc_value = readl(adcdat) & 0xfff;
       temp_value = 9999 * adc_value / 4095;
      
       return temp_value;
}
 
long adc_ioctl (struct file *filp, unsigned int cmd, unsigned long arg)
{
       //printk("%s:%s:%d\n", __FILE__, __func__, __LINE__);
 
       switch (cmd) {
       case ADC_CMD_GET:
              *(unsigned int *)arg = adc_get();
              break;
       default:
              return -EINVAL;
       }
       return 0;
}
 
struct file_operations fops = {
       .owner           = THIS_MODULE,
       .unlocked_ioctl      = adc_ioctl,
};
 
int adc_init(void)
{
       int ret;
       int major;
       struct device *pdevice = NULL;
 
       //printk("%s:%s:%d\n", __FILE__, __func__, __LINE__);
      
       ret = alloc_chrdev_region(&dev, minor_base, adc_count, adc_name);
       if (0 > ret) {
              printk("Can't get device number\n");
              return ret;
       }
             
       pcdev = cdev_alloc();
       if (NULL == pcdev) {
              printk("cdev alloc failed.\n");
              ret = -ENOMEM;
              goto UNREG_DEV_NUM;
       }
             
       cdev_init(pcdev, &fops);
       pcdev->owner = THIS_MODULE;
      
       ret = cdev_add(pcdev, dev, adc_count);
       if (0 > ret) {
              printk("add cdev failed.\n");
              goto DEL_CDEV;
       }
 
       pcls = class_create(pcdev->owner, adc_name);
       if (IS_ERR(pcls)) {
              printk("class create failed.\n");
              ret = PTR_ERR(pcls);
              goto DEL_CDEV;
       }
      
       major = MAJOR(dev);
       pdevice = device_create(pcls, NULL, MKDEV(major, minor_base), NULL, "%s%d", adc_name, minor_base);
       if (IS_ERR(pdevice)) {
              printk("device %s%d create failed.\n", adc_name, minor_base);
              ret = PTR_ERR(pdevice);
              goto DESTROY_CLASS;
       }
 
       //printk("Body temperature module init done!\n");
      
       if (0 != AdcInit())
       {
              goto DESTROY_CLASS;
       }
       printk("adc init\n");
       return 0;
 
DESTROY_CLASS:
       class_destroy(pcls);
DEL_CDEV:
       cdev_del(pcdev);
UNREG_DEV_NUM:
       unregister_chrdev_region(dev, adc_count); 
 
       return ret;
}
 
void adc_exit(void)
{
       device_destroy (pcls, MKDEV(MAJOR(dev), minor_base));    
       class_destroy(pcls);
       cdev_del(pcdev);
       unregister_chrdev_region(dev, adc_count); 
       printk("Good bye, adc module\n");
       //printk("%s:%s:%d\n", __FILE__, __func__, __LINE__);
}
 
module_init(adc_init);
module_exit(adc_exit);
 
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Ruth Wei");
MODULE_DESCRIPTION("adc for demo");
MODULE_VERSION("1.0.1");
2. 编译测试
经过交叉编译后，加载驱动，写一个应用程序可以读取ADC转换后的值。
      四、总结
      本文从模数转换器的技术指标和电路连接等方面进行分析，最终写出驱动程序，可以在4412板子上进行测试。