125KHZ RFID 曼彻斯特码在内核域解码

一. 曼彻斯特码理论分析：
曼彻斯特码编码的ID卡每次输出64bit 数据/8个字节，其载波编码为曼彻斯特码.
其时序图如下:

曼彻斯特码调制方式下，EM4100卡片每传送一位数据的时间是64个振荡周期。125KHZ载波时，卡片传送一bit数据理论频率为125KHz / 64 = 1.953125KHz。那么得到一个周期为:1 000 000us / 1.953125KHz = 512us。

也就是说：曼彻斯特码一个完整的数据跳变为一个周期（512us）。
但是特别需要注意的是：存在空跳则半个跳变为半个周期（256us）。

那么如何得到一个bit的数据呢？

如果捕获到一个电平变化，这个电平距离上次检测到电平变化时间为512us，则该位按以下读取：低电平-bit = 1，高电平-bit = 0;如果捕获到一个电平变化，这个电平距离上次检测到电平变化时间256us，则此次不作判断，再次捕获到一个边沿时再判断如下：上次bit = 1 此次bit = 1,上次bit = 0,此次bit = 0.
此处有一个特别注意的地方，如果上次读取到256us，不管这次读取间隔是256us还是512us，都应该读取上一次的电平，并且重新检测跳包。

二.设备树配置：
配置设备树节点，用于内核驱动程序找到对应能检波的IO口。在anyka v300 平台如下：

编辑：anycloud_ak39ev330_common.dtsi
添加节点：在 gpiokeys: gpiokeys {
compatible = "anyka,ak39ev330-gpiokeys";status = "disable";};附近添加以下节点信息：rfid_control: rfid_control {compatible = "leo_rfid_control";status = "disable";};编辑：C500_SQ38_AK3918EV330_GC2063_MIPI_V1.0.0.dts：在"$gpio" 节点内部添加rfid_pins:rfid_pins{anyka,pins = <0>;anyka,function = <0>;anyka,pull = <0x00000001>;};然后退出$gpio节点，使能“rfid_control”节点，如下：&rfid_control{gpios = <&gpio 0 1>;pinctrl-names ="default";pinctrl-0 = <&rfid_pins>;status = "okay";};

好了，完成了设备树信息的编写，

第二部：接下来开始写驱动内核程序。
整个代码如下：

#include <linux/module.h>
#include <linux/poll.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/miscdevice.h>
#include <linux/kernel.h>
#include <linux/major.h>
#include <linux/mutex.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/kmod.h>
#include <linux/gfp.h>
#include <linux/gpio/consumer.h>
#include <linux/platform_device.h>
#include <linux/of_gpio.h>
#include <linux/of_irq.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/slab.h>
#include <linux/fcntl.h>
#include <linux/timer.h>
#include <linux/workqueue.h>
#include <asm/current.h>
#include <linux/kthread.h>
#include <linux/delay.h>#define diff_us(t1,t2) ((u64)t1.tv_sec - (u64)t2.tv_sec) * 1000000 + ((u64)t1.tv_usec - (u64)t2.tv_usec);#define rfid_code_bit_value(data,index) ((data[(index)/8] >> (7 - (index)%8))&0x01)
/* 主设备号 */
static int major = 0;
/* 创建设备类的结构体 */
static struct class* rfid_class;
/* 记录设备树信息的结构体*/
static int rfid_gpio_index;static struct task_struct *rfid_kthread;   static char rfid_data_code[16] = {0};
static int rfid_data_count = 0;static char rfid_code_number[4] = {0};
static char rfid_code_number_ready = 0;static DEFINE_MUTEX(rfid_code_mutex);static ssize_t rfid_read(struct file* file,char __user*buf,size_t size,loff_t* offset){int len  = 0;if(size < 4){return 0;}len = sizeof(rfid_code_number);//printk("read rfid value \n");	mutex_lock(&rfid_code_mutex);if(rfid_code_number_ready == 0){mutex_unlock(&rfid_code_mutex);return 0;}copy_to_user(buf, rfid_code_number , len); rfid_code_number_ready = 0;mutex_unlock(&rfid_code_mutex);return len;
}
/* 创建设备方法 */
static struct file_operations rfid_control_fops = {.owner = THIS_MODULE,.read = rfid_read,
};static int rfid_code_leave_wait(int* level,int min,int middle,int max,struct timeval* pre_tv){u64 us = 0;struct timeval tv;int cur_level = gpio_get_value(rfid_gpio_index) ;while(gpio_get_value(rfid_gpio_index) == cur_level){do_gettimeofday(&tv);us = diff_us(tv,(*pre_tv));if(us > max){return -1;}}do_gettimeofday(&tv);us = diff_us(tv,(*pre_tv));*level = cur_level?0:1;if(us < min){return -1;}else if((us > min)&&(us < middle)){return 0;}return 1;
}static char rfid_code_jump_flg = 0;static int rfid_code_read_proc(void){int i = 0;int reslut = 0;int level = 0;struct timeval tv;unsigned char value = 0;memset(rfid_data_code,0,sizeof(rfid_data_code));rfid_data_count = 0;rfid_code_jump_flg = 0;do_gettimeofday(&tv);while(1){reslut = rfid_code_leave_wait(&level,125,375,625,&tv);do_gettimeofday(&tv);if((reslut == 0)&&(rfid_code_jump_flg == 0)){rfid_code_jump_flg = 1;}else if((reslut == 1)||((reslut == 0)&&(rfid_code_jump_flg == 1))){if(rfid_code_jump_flg == 1){value = ((rfid_data_code[(rfid_data_count - 1) / 8] >> (7 - (rfid_data_count - 1) % 8)) & 0x01) ? 1 : 0;}else{value = level?0:1;}rfid_code_jump_flg = 0;rfid_data_code[rfid_data_count / 8] |= (value << (7 - rfid_data_count % 8));rfid_data_count++;if(rfid_data_count >= 128){return 1;}}else if(reslut < 0){return -1;}}return 0;
}static int rfid_code_data_check(void){int index = 0,i = 0,j = 0,n = 0;int value = 0;for(index = 0; index < 64 ; index++){value = 0;for(i = 0 ; i < 9 ; i++){value <<= 1;value |= rfid_code_bit_value(rfid_data_code,index + i);//printk("%d",rfid_code_bit_value(rfid_data_code,index + i));}if(value == 0x1FF){index += 9;break;}}if(index == 64){printk("check rfid data failed (%s,%d)\n",__func__,__LINE__);return -1;}for(i = index; i < (index + 45) ; i+=5){value = 0;for( j = 0 ;j < 4 ; j++){value += rfid_code_bit_value(rfid_data_code,i + j);}if((value %2) != rfid_code_bit_value(rfid_data_code,i + j)){printk("check rfid data failed (%s,%d)\n",__func__,__LINE__);return -1;}}for( i = index; i < (index + 4) ; i++){value = 0;for( j = 0 ; j < 50 ; j+= 5){value += rfid_code_bit_value(rfid_data_code,i + j);}if((value %2) != rfid_code_bit_value(rfid_data_code,i + j)){printk("check rfid data failed (%s,%d)\n",__func__,__LINE__);return -1;}}if(rfid_code_bit_value(rfid_data_code,index + 54) != 0){printk("stop failed \n");return -1;}n = 0;mutex_lock(&rfid_code_mutex);rfid_code_number_ready = 0;mutex_unlock(&rfid_code_mutex);memset(rfid_code_number,0,sizeof(rfid_code_number));for(i = index + 10 ; i < (index + 50) ; i+=10){value = 0;for( j = 0 ; j < 9; j++){if(j == 4){continue;}value <<= 1;value |= rfid_code_bit_value(rfid_data_code,i+j);}rfid_code_number[n++] = value;//printk("%02x ",value);}//printk("\n");mutex_lock(&rfid_code_mutex);rfid_code_number_ready = 1;mutex_unlock(&rfid_code_mutex);return 1;
}static int k_rfid_task(void*data){int pre_level = gpio_get_value(rfid_gpio_index);int cur_level = pre_level;char det_start_flag = 0;printk("leo:kernel rfid card task success! \n");while(1){if(kthread_should_stop()){break;}if(det_start_flag == 0){cur_level = gpio_get_value(rfid_gpio_index);if(cur_level == 0){det_start_flag = 1;pre_level = cur_level;}else{msleep(100);}}else{if(rfid_code_read_proc() == 1){//printk("check data \n");rfid_code_data_check();	}gpio_set_value(rfid_gpio_index,1);pre_level = gpio_get_value(rfid_gpio_index);det_start_flag = 0;msleep(10);}}return 0;
}static int rfid_probe(struct platform_device*pdev){int irq;struct device_node *np = pdev->dev.of_node;printk("leo:rfid probe success \n");rfid_gpio_index = of_get_named_gpio(np, "gpios", 0);if(rfid_gpio_index < 0){printk("rfid gpio setting failed\n");}else{printk("rfid setting gpio%d\n",rfid_gpio_index);}device_create(rfid_class,NULL,MKDEV(major,0),NULL,"rfid_control");gpio_direction_output(rfid_gpio_index,1);msleep(100);gpio_direction_input(rfid_gpio_index);mutex_init(&rfid_code_mutex);rfid_kthread = kthread_create(k_rfid_task,NULL,"rfid_kthread");if(IS_ERR(rfid_kthread)){printk("create rfid_kthread faield\n");return 0;}wake_up_process(rfid_kthread);return 0;	
}static int rfid_remove(struct platform_device*pdev)
{int irq;printk("leo:rfid driver remove\n");kthread_stop(rfid_kthread);device_destroy(rfid_class,MKDEV(major,0));return 0;
}static const struct of_device_id rfid_board_control[]={{.compatible = "leo_rfid_control"},{}
};static struct platform_driver rfid_platform_drv = {.probe = rfid_probe,.remove = rfid_remove,.driver = {.name = "rfid_control",.of_match_table = rfid_board_control,},
};static int __init rfid_drv_init(void){printk("leo:rfid drv init start\n");//注册主字符设备号major = register_chrdev(0,"rfid_control",&rfid_control_fops);//创建设备类rfid_class = class_create(THIS_MODULE,"rfid_class");if(IS_ERR(rfid_class)){printk("rfid class create failed\n");unregister_chrdev(major,"rfid_control");return PTR_ERR(rfid_class);}return platform_driver_register(&rfid_platform_drv);
}static void __exit rfid_drv_exit(void){platform_driver_unregister(&rfid_platform_drv);class_destroy(rfid_class);unregister_chrdev(major,"rfid_control");
}/*
* ko创建
*/
module_init(rfid_drv_init);
module_exit(rfid_drv_exit);MODULE_LICENSE("GPL");

生成rfid.ko之后，上次insom rfid.ko,完成内核模块的安装。
第三步：应用层的编写：
整体代码如下：

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>#define RFID_DEVICE_PATH "/dev/rfid_control"int main(int argc,char** argv){if(access(RFID_DEVICE_PATH,F_OK) != 0){printf("%s not exit\n",RFID_DEVICE_PATH);return 0;}int fd = open(RFID_DEVICE_PATH,O_RDONLY);if(fd < 0 ){printf("open %s failed \n",RFID_DEVICE_PATH);return 0;}unsigned char data[4] = {0};while(1){if(read(fd,data,sizeof(data)) == 4){printf("%02x%02x%02x%02x\n",data[0],data[1],data[2],data[3]);}usleep(1000*10);}return 0;
}