linux adc is a hybrid device driver; in linux2.6.30.4, the system already comes with the ADC universal driver file "arch/arm/plat-s3c24xx/adc.c", which is based on the platform driver It is written according to the architecture of the device model, and contains some relatively general and stable codes.
The operating environment of this tutorial: linux2.6.30.4 system, Dell G3 computer.
What kind of device is linux adc?
linux mixed device driver adc driver
In linux2.6.30.4, the system has been automatically It comes with the ADC universal driver file ---arch/arm/plat-s3c24xx/adc.c, which is written based on the architecture of the platform driver device model. It contains some relatively common and stable codes, but linux2.6.30.4 The version of the ADC universal driver file is not complete, and there is no reading function. Later, I took a look at the ADC general file of the Linux 3.8 version - arch/arm/plat-samsung/adc.c which is relatively complete.
But this section is not to analyze this file, but to write the ADC driver in another architecture. Because the ADC driver is relatively simple, it is not used. The platform driver device model is written for the architecture, this time we use a misc device driver.
Q: What is a misc device driver?
Answer: miscdevice shares a major device number MISC_MAJOR (10), but the minor device numbers are different. All miscdevice devices form a linked list. When accessing the device, the kernel searches for the corresponding miscdevice device based on the device number, and then calls the file operation interface registered in its file_operations structure to operate.
struct miscdevice {
int minor; //次设备号，如果设置为MISC_DYNAMIC_MINOR则系统自动分配
const char *name; //设备名
const struct file_operations *fops; //操作函数
struct list_head list;
struct device *parent;
struct device *this_device;
};
static int __init dev_init(void)
{
int ret;
base_addr=ioremap(S3C2410_PA_ADC,0x20);
if (base_addr == NULL)
{
printk(KERN_ERR "failed to remap register block\n");
return -ENOMEM;
}
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);
ADCTSC = 0;
ret = request_irq(IRQ_ADC, adcdone_int_handler, IRQF_SHARED, DEVICE_NAME, &adcdev);
if (ret)
{
iounmap(base_addr);
return ret;
}
ret = misc_register(&misc);
printk (DEVICE_NAME" initialized\n");
return ret;
}adcdone_int_handler, and the flags is IRQF_SHARED, which is a shared interrupt, because the touch screen also needs to apply for the ADC interrupt, and finally register a hybrid equipment.
When the application opens ("/dev/adc",...), the open function in the driver will be called, so let's take a look See what the open function does?
static int tq2440_adc_open(struct inode *inode, struct file *filp)
{
/* 初始化等待队列头 */
init_waitqueue_head(&(adcdev.wait));
/* 开发板上ADC的通道2连接着一个电位器 */
adcdev.channel=2; //设置ADC的通道
adcdev.prescale=0xff;
DPRINTK( "ADC opened\n");
return 0;
}When the application reads, the read function in the driver will be called. So let’s take a look at what the read function does?
static ssize_t tq2440_adc_read(struct file *filp, char *buffer, size_t count, loff_t *ppos)
{
char str[20];
int value;
size_t len;
/* 尝试获得ADC_LOCK信号量，如果能够立刻获得，它就获得信号量并返回0
* 否则，返回非零，它不会导致调用者睡眠,可以在中断上下文使用
*/
if (down_trylock(&ADC_LOCK) == 0)
{
/* 表示A/D转换器资源可用 */
ADC_enable = 1;
/* 使能预分频，选择ADC通道，最后启动ADC转换*/
START_ADC_AIN(adcdev.channel, adcdev.prescale);
/* 等待事件，当ev_adc = 0时，进程被阻塞，直到ev_adc>0 */
wait_event_interruptible(adcdev.wait, ev_adc);
ev_adc = 0;
DPRINTK("AIN[%d] = 0x%04x, %d\n", adcdev.channel, adc_data, ((ADCCON & 0x80) ? 1:0));
/* 将在ADC中断处理函数读取的ADC转换结果赋值给value */
value = adc_data;
sprintf(str,"%5d", adc_data);
copy_to_user(buffer, (char *)&adc_data, sizeof(adc_data));
ADC_enable = 0;
up(&ADC_LOCK);
}
else
{
/* 如果A/D转换器资源不可用，将value赋值为-1 */
value = -1;
}
/* 将ADC转换结果输出到str数组里，以便传给应用空间 */
len = sprintf(str, "%d\n", value);
if (count >= len)
{
/* 从str数组里拷贝len字节的数据到buffer，即将ADC转换数据传给应用空间 */
int r = copy_to_user(buffer, str, len);
return r ? r : len;
}
else
{
return -EINVAL;
}
}Q: When is ev_adc>0? Default ev_adc = 0
Answer: In the adcdone_int_handler interrupt processing function, after the data is read out, ev_adc is set to 1.
ADC interrupt handler function adcdone_int_handler
##
/* ADC中断处理函数 */
static irqreturn_t adcdone_int_handler(int irq, void *dev_id)
{
/* A/D转换器资源可用 */
if (ADC_enable)
{
/* 读ADC转换结果数据 */
adc_data = ADCDAT0 & 0x3ff;
/* 唤醒标志位，作为wait_event_interruptible的唤醒条件 */
ev_adc = 1;
wake_up_interruptible(&adcdev.wait);
}
return IRQ_HANDLED;
}1. In the open function, set the analog input channel and set the prescaler value
2. In the read function, AD conversion is started and the process sleeps
三、adc_irq函数里，AD转换结束后触发ADC中断，在ADC中断处理函数将数据读出，唤醒进程
四、read函数里，进程被唤醒后，将adc转换数据传给应用程序
ADC驱动参考源码：
/************************************* NAME:EmbedSky_adc.c COPYRIGHT:www.embedsky.net *************************************/ #include#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "tq2440_adc.h" #undef DEBUG //#define DEBUG #ifdef DEBUG #define DPRINTK(x...) {printk(KERN_DEBUG "EmbedSky_adc: " x);} #else #define DPRINTK(x...) (void)(0) #endif #define DEVICE_NAME "adc" /* 设备节点: /dev/adc */ static void __iomem *base_addr; typedef struct { wait_queue_head_t wait; /* 定义等待队列头 */ int channel; int prescale; }ADC_DEV; DECLARE_MUTEX(ADC_LOCK); /* 定义并初始化信号量,并初始化为1 */ static int ADC_enable = 0; /* A/D转换器资是否可用标志位 */ static ADC_DEV adcdev; /* 用于表示ADC设备 */ static volatile int ev_adc = 0; /* 作为wait_event_interruptible的唤醒条件 */ static int adc_data; static struct clk *adc_clock; #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 #define PRESCALE_DIS (0 << 14) #define PRESCALE_EN (1 << 14) #define PRSCVL(x) ((x) << 6) #define ADC_INPUT(x) ((x) << 3) #define ADC_START (1 << 0) #define ADC_ENDCVT (1 << 15) /* 使能预分频，选择ADC通道，最后启动ADC转换*/ #define START_ADC_AIN(ch, prescale) \ do{ ADCCON = PRESCALE_EN | PRSCVL(prescale) | ADC_INPUT((ch)) ; \ ADCCON |= ADC_START; \ }while(0) /* ADC中断处理函数 */ static irqreturn_t adcdone_int_handler(int irq, void *dev_id) { /* A/D转换器资源可用 */ if (ADC_enable) { /* 读ADC转换结果数据 */ adc_data = ADCDAT0 & 0x3ff; /* 唤醒标志位，作为wait_event_interruptible的唤醒条件 */ ev_adc = 1; wake_up_interruptible(&adcdev.wait); } return IRQ_HANDLED; } static ssize_t tq2440_adc_read(struct file *filp, char *buffer, size_t count, loff_t *ppos) { char str[20]; int value; size_t len; /* 尝试获得ADC_LOCK信号量，如果能够立刻获得，它就获得信号量并返回0 * 否则，返回非零，它不会导致调用者睡眠,可以在中断上下文使用 */ if (down_trylock(&ADC_LOCK) == 0) { /* 表示A/D转换器资源可用 */ ADC_enable = 1; /* 使能预分频，选择ADC通道，最后启动ADC转换*/ START_ADC_AIN(adcdev.channel, adcdev.prescale); /* 等待事件，当ev_adc = 0时，进程被阻塞，直到ev_adc>0 */ wait_event_interruptible(adcdev.wait, ev_adc); ev_adc = 0; DPRINTK("AIN[%d] = 0x%04x, %d\n", adcdev.channel, adc_data, ((ADCCON & 0x80) ? 1:0)); /* 将在ADC中断处理函数读取的ADC转换结果赋值给value */ value = adc_data; sprintf(str,"%5d", adc_data); copy_to_user(buffer, (char *)&adc_data, sizeof(adc_data)); ADC_enable = 0; up(&ADC_LOCK); } else { /* 如果A/D转换器资源不可用，将value赋值为-1 */ value = -1; } /* 将ADC转换结果输出到str数组里，以便传给应用空间 */ len = sprintf(str, "%d\n", value); if (count >= len) { /* 从str数组里拷贝len字节的数据到buffer，即将ADC转换数据传给应用空间 */ int r = copy_to_user(buffer, str, len); return r ? r : len; } else { return -EINVAL; } } static int tq2440_adc_open(struct inode *inode, struct file *filp) { /* 初始化等待队列头 */ init_waitqueue_head(&(adcdev.wait)); /* 开发板上ADC的通道2连接着一个电位器 */ adcdev.channel=2; //设置ADC的通道 adcdev.prescale=0xff; DPRINTK( "ADC opened\n"); return 0; } static int tq2440_adc_release(struct inode *inode, struct file *filp) { DPRINTK( "ADC closed\n"); return 0; } static struct file_operations dev_fops = { owner: THIS_MODULE, open: tq2440_adc_open, read: tq2440_adc_read, release: tq2440_adc_release, }; static struct miscdevice misc = { .minor = MISC_DYNAMIC_MINOR, .name = DEVICE_NAME, .fops = &dev_fops, }; static int __init dev_init(void) { int ret; base_addr=ioremap(S3C2410_PA_ADC,0x20); if (base_addr == NULL) { printk(KERN_ERR "failed to remap register block\n"); return -ENOMEM; } 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); ADCTSC = 0; ret = request_irq(IRQ_ADC, adcdone_int_handler, IRQF_SHARED, DEVICE_NAME, &adcdev); if (ret) { iounmap(base_addr); return ret; } ret = misc_register(&misc); printk (DEVICE_NAME" initialized\n"); return ret; } static void __exit dev_exit(void) { free_irq(IRQ_ADC, &adcdev); iounmap(base_addr); if (adc_clock) { clk_disable(adc_clock); clk_put(adc_clock); adc_clock = NULL; } misc_deregister(&misc); } EXPORT_SYMBOL(ADC_LOCK); module_init(dev_init); module_exit(dev_exit); MODULE_LICENSE("GPL"); MODULE_AUTHOR("www.embedsky.net"); MODULE_DESCRIPTION("ADC Drivers for EmbedSky SKY2440/TQ2440 Board and support touch");
/*************************************
NAME:EmbedSky_adc.c
COPYRIGHT:www.embedsky.net
*************************************/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <linux/fs.h>
#include <errno.h>
#include <string.h>
int main(void)
{
int fd ;
char temp = 1;
fd = open("/dev/adc", 0);
if (fd < 0)
{
perror("open ADC device !");
exit(1);
}
for( ; ; )
{
char buffer[30];
int len ;
len = read(fd, buffer, sizeof buffer -1);
if (len > 0)
{
buffer[len] = '\0';
int value;
sscanf(buffer, "%d", &value);
printf("ADC Value: %d\n", value);
}
else
{
perror("read ADC device !");
exit(1);
}
sleep(1);
}
adcstop:
close(fd);
}
[WJ2440]# ./adc_test ADC Value: 693 ADC Value: 695 ADC Value: 694 ADC Value: 695 ADC Value: 702 ADC Value: 740 ADC Value: 768 ADC Value: 775 ADC Value: 820 ADC Value: 844 ADC Value: 887 ADC Value: 937 ADC Value: 978 ADC Value: 1000 ADC Value: 1023 ADC Value: 1023 ADC Value: 1023
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