RK3568笔记五十二：HC-SR04超声波模块驱动测试
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一、HC-SR04简介
HC-SR04超声波模块是一种常用于距离测量和障碍物检测的模块。它通过发射超声波信号并接收回波来计算所测量物体与传感器之间的距离。
1、基本原理
TRIG引脚负责发送超声波脉冲串。此引脚应设置为高电平10μs，此时HC-SR04将以40 kHZ发出8个周期的声波脉冲。发出声波爆发后，ECHO引脚将变为高电平。 ECHO引脚是数据引脚 - 用于进行距离测量。发送超声波脉冲串后， ECHO引脚将变为高电平，它将保持高电平，直到检测到超声波脉冲串为止，此时它将变为低电平。
2、计算公式
我们知道声速是340m/s
根据x=vt
因为超声波发送出去和回来是测量距离的两倍，所以假设距离是L
2L=344xt
t我们用定时器测出来
一般都是us
所以就是tx172x10的-6次方=L，L单位为cm
最终的出 L= t(us) * 0.0172(cm/us)
0.0172=1/58
所以 L= t(us)/58（cm）
3、程序原理
设置Echo引脚为双边沿触发，在上升沿触发中断时记录此刻时刻T0，在下降沿触发中断时记录时刻T1
高电平时间 = T1 - T0
内核中获取时间的API ：
ktime_get_ns(); // 获取内核启动到现在的时间，在挂起时会暂停
ktime_get_boottime_ns(); // 获取内核启动到现在的时间，不受挂起影响，是绝对时间
ktime_get_real_ns(); // 获取Unix时间(1970年)到现在的时间，可能涉及闰秒更新，用得比较少
ktime_get_raw_ns(); // 类似ktime_get_ns(),不涉及闰秒更新，用得比较少三、硬件原理
HC-SR04超声波模块和ATK-DLRK3568的接线如下：
| HC-SR04 | RK3568 |
| VCC | 3.3V |
| Trig | GPIO3 PC5 |
| Echo | GPIO3 PC4 |
| Gnd | GND |
四、设备树
1、设备树节点
修/home/alientek/rk3568_linux_sdk/kernel/arch/arm64/boot/dts/rockchip/目录下的rk3568-atk-evb1-ddr4-v10.dtsi文件，在文中添加代码，在设备树下添加hc_sr04节点。
hc_sr04 {compatible = "hc_sr04";pinctrl-names = "default";status = "okay";trig {compatible = "trig-test";pinctrl-0 = <&pinctrl_trig>;gpios-trig = <&gpio3 RK_PC5 GPIO_ACTIVE_HIGH>;status = "okay";};echo {compatible = "echo-test";pinctrl-0 = <&pinctrl_echo>;gpios-echo = <&gpio3 RK_PC4 GPIO_ACTIVE_HIGH>;status = "okay";};};
2、创建设备的 pinctrl 节点
修改/home/alientek/rk3568_linux_sdk/kernel/arch/arm64/boot/dts/rockchip/目录下的rk3568-pinctrl.dtsi文件，在最后面增加节点
trig-gpio {/omit-if-no-ref/pinctrl_trig: trig-gpio-ctrl {rockchip,pins = <3 RK_PC5 RK_FUNC_GPIO &pcfg_pull_none>;};};echo-gpio {/omit-if-no-ref/pinctrl_echo: echo-gpio-ctrl {rockchip,pins = <3 RK_PC4 RK_FUNC_GPIO &pcfg_pull_none>;};};
设备树修改完成以后在 SDK 顶层目录输入如下命令重新编译一下内核：
# 指定 SDK 的板级配置文件
./build.sh lunch
# 编译内核
./build.sh kernel编译完成以后得到 boot.img, boot.img 就是编译出来的内核+设备树打包在一起的文件
只需要重新烧写boot.img。
烧写完成以后启动开发板。Linux 启动成功以后进入到/proc/device-tree/目录中查看是否有节点
会有一个hc-sr04节点，节点下又有trig和echo两个子节点。
在proc/device-tree/hc_sr04/下
五、驱动编写
1、sr04_drv.c
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/uaccess.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/ide.h>
#include <linux/errno.h>
#include <linux/gpio.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_gpio.h>
#include <asm/io.h>
#include <linux/device.h>
#include <linux/timer.h>
#include <linux/jiffies.h>
#include <linux/platform_device.h>
#include <linux/of_irq.h>
#include <linux/wait.h>
#include <linux/sched/signal.h>
#include <linux/poll.h>
#include <linux/atomic.h>#define HC_SR04_DTS_NAME "hc_sr04"#define DEV_NAME "hc-sr04"struct hc_sr04 {int irq; /* 中断号 */int trig_gpio; /* trig-gpio */int echo_gpio; /* echo-gpio */dev_t dev_no; /* 设备号 */ struct cdev chrdev; struct class *class;struct device_node *nd[2]; wait_queue_head_t wq; /* 等待队列 */
};static struct hc_sr04 sr04;
static int sr04_data_ns = 0;int led_flag = 0;/* 使设备只能被一个进程打开 */
static int sr04_drv_open(struct inode *node, struct file *file)
{printk("hc-sr04 open\n");gpio_direction_input(sr04.echo_gpio); gpio_direction_output(sr04.trig_gpio, 0);return 0;
}static ssize_t sr04_drv_read(struct file *filp, char __user *buf, size_t size, loff_t *offset)
{int ret;int timeout;unsigned long flags;/* 中断屏蔽 */local_irq_save(flags);/* 启动触发信号 */gpio_set_value(sr04.trig_gpio, 1); udelay(30);gpio_set_value(sr04.trig_gpio, 0); /* 恢复中断 */local_irq_restore(flags);timeout = wait_event_interruptible_timeout(sr04.wq, sr04_data_ns, HZ); /* wait 1 sec */if (!timeout) return -EAGAIN;if (copy_to_user(buf, &sr04_data_ns, size > 4 ? 4 : size)) {ret = -EFAULT;} else {ret = size;}sr04_data_ns = 0;return ret;
}static irqreturn_t hc_sr04_isr(int irq_num, void *dev)
{if (gpio_get_value(sr04.echo_gpio)){sr04_data_ns = ktime_get_ns();}else{sr04_data_ns = ktime_get_ns() - sr04_data_ns;wake_up(&sr04.wq); /* 唤醒等待队列中进入休眠的进程 */}return IRQ_RETVAL(IRQ_HANDLED);
}static int sr04_drv_release(struct inode *node, struct file *file)
{printk("hc-sr04 release\n");return 0;
}static struct file_operations sr04_drv_ops = { .owner = THIS_MODULE,.open = sr04_drv_open,.read = sr04_drv_read,.release = sr04_drv_release,
};/* 设备树的匹配列表 */
static struct of_device_id dts_match_table[] = {{.compatible = HC_SR04_DTS_NAME, }, /* 通过设备树来匹配 */
};static int sr04_driver_probe(struct platform_device *pdev)
{ int err;int ret;struct device *sr04_dev;struct property *proper;struct device_node *node = pdev->dev.of_node;if (!node) { printk("hc-sr501 dts node can not found!\r\n"); return -EINVAL; }sr04.nd[0] = of_find_node_by_path("/hc_sr04/trig"); if (IS_ERR(sr04.nd[0])) { printk("hc-sr04 DTS Node not found!\r\n"); return PTR_ERR(sr04.nd[0]); }sr04.trig_gpio = of_get_named_gpio(sr04.nd[0], "gpios-trig", 0); /* 获取trig-gpio的编号 */if (sr04.trig_gpio < 0) {printk("trig-gpio not found!\r\n"); return -EINVAL;}err = gpio_request(sr04.trig_gpio, "gpios-trig"); if(err) {printk("gpio_request trig-gpios is failed!\n");return -EINVAL;}/* 3、设置为输出 */ret = gpio_direction_output(sr04.trig_gpio, 1);if(ret < 0) {printk("can't set sr04.trig_gpio!\r\n");}/*获取字节点的compatible属性*/proper = of_find_property(sr04.nd[0], "compatible", NULL);if(proper == NULL) {printk("compatible property find failed\r\n");} else {printk("led compatible = %s\r\n", (char*)proper->value);}sr04.nd[1] = of_find_node_by_path("/hc_sr04/echo"); if (IS_ERR(sr04.nd[1])) { printk("hc-sr04 DTS Node not found!\r\n"); return PTR_ERR(sr04.nd[1]); }sr04.echo_gpio = of_get_named_gpio(sr04.nd[1], "gpios-echo", 0); /* 获取echo-gpio的编号 */if ( sr04.echo_gpio < 0) {printk("echo-gpio not found!\r\n"); return -EINVAL;}err = gpio_request(sr04.echo_gpio, "echo-gpios"); if(err) {gpio_free(sr04.trig_gpio);printk("gpio_request echo-gpios is failed!\n");return -EINVAL;}printk("trig-gpio %d echo-gpio %d\n", sr04.trig_gpio, sr04.echo_gpio);sr04.irq = gpio_to_irq(sr04.echo_gpio);err = request_irq(sr04.irq, hc_sr04_isr, IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING, DEV_NAME, NULL); /* 申请中断 */if (err) {printk(KERN_INFO"failed to request irq %d\r\n", sr04.irq);gpio_free(sr04.trig_gpio);gpio_free(sr04.echo_gpio);return err;}/* 内核自动分配设备号 */err = alloc_chrdev_region(&sr04.dev_no, 0, 1, DEV_NAME); if (err < 0) {pr_err("Error: failed to register mbochs_dev, err: %d\n", err);return err;}cdev_init(&sr04.chrdev, &sr04_drv_ops);cdev_add(&sr04.chrdev, sr04.dev_no, 1);sr04.class = class_create(THIS_MODULE, DEV_NAME);if (IS_ERR(sr04.class)) { err = PTR_ERR(sr04.class);goto failed1;}/* 创建设备节点 */sr04_dev = device_create(sr04.class , NULL, sr04.dev_no, NULL, DEV_NAME); if (IS_ERR(sr04_dev)) { /* 判断指针是否合法 */err = PTR_ERR(sr04_dev);goto failed2;}init_waitqueue_head(&sr04.wq); /* 初始化等待队列头 */printk("hc-sr04 probe success\r\n");return 0;
failed2:device_destroy(sr04.class, sr04.dev_no);class_destroy(sr04.class);
failed1:unregister_chrdev_region(sr04.dev_no, 1);cdev_del(&sr04.chrdev);return err;
}static int sr04_driver_remove(struct platform_device *pdev)
{device_destroy(sr04.class, sr04.dev_no);class_destroy(sr04.class);unregister_chrdev_region(sr04.dev_no, 1);cdev_del(&sr04.chrdev);free_irq(sr04.irq, NULL); /* 释放中断*/gpio_free(sr04.trig_gpio);gpio_free(sr04.echo_gpio);printk(KERN_INFO"hc-sr04 drv remove success\n");return 0;
}static struct platform_driver _platform_driver = {.probe = sr04_driver_probe,.remove = sr04_driver_remove,.driver = {.name = HC_SR04_DTS_NAME,.owner = THIS_MODULE,.of_match_table = dts_match_table, /* 通过设备树匹配 */},
};/* 入口函数 */
static int __init _driver_init(void)
{int ret;printk("hc-sr04 %s\n", __FUNCTION__);ret = platform_driver_register(&_platform_driver); //注册platform驱动return ret;
}/* 出口函数 */
static void __exit _driver_exit(void)
{printk("hc-sr04 %s\n", __FUNCTION__);platform_driver_unregister(&_platform_driver);
}module_init(_driver_init);
module_exit(_driver_exit);MODULE_AUTHOR("yifeng");
MODULE_LICENSE("GPL");
2、makefile
KERNELDIR := /home/alientek/rk3568_linux_sdk/kernel
ARCH=arm64
CROSS_COMPILE=/opt/atk-dlrk356x-toolchain/usr/bin/aarch64-buildroot-linux-gnu-export ARCH CROSS_COMPILECURRENT_PATH := $(shell pwd)
obj-m := sr04_drv.obuild: kernel_moduleskernel_modules:$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) modules
clean:$(MAKE) -C $(KERNELDIR) M=$(CURRENT_PATH) clean
编译
六、APP应用程序
sr04App.c
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <sys/ioctl.h>
#include <poll.h>#define DEV_NAME "/dev/hc-sr04"void sleep_ms(unsigned int ms)
{struct timeval delay;delay.tv_sec = 0;delay.tv_usec = ms * 1000; select(0, NULL, NULL, NULL, &delay);
}int main(int argc, char **argv)
{int fd;int ret;struct pollfd fds[1];/* 2. 打开文件 */fd = open(DEV_NAME, O_RDWR); // | O_NONBLOCKif (fd < 0){printf("can not open file %s, %d\n", DEV_NAME, fd);return -1;}int time_ns;while (1){if ((ret = read(fd, &time_ns, 4)) == 4){printf("time %d ns %d ms, distance %d mm %d cm\r\n", time_ns, time_ns/1000000, time_ns*340/2/1000000, time_ns*340/2/1000000/10);}else{printf("not get time, err %d\r\n", ret);}sleep_ms(2000);}close(fd);return 0;
}
编译
/opt/atk-dlrk356x-toolchain/bin/aarch64-buildroot-linux-gnu-gcc sr04App.c -o sr04App
七、测试
把生成的ko文件和sr04App文件拷贝到开发板。
加载驱动
insmod sr04_drv.ko 
加载完后，会在dev下查到hc-sr04
测试
./sr04App 
驱动采用的是中断方式，比较常用的方法。
也可以用等待方式，但不建议，自行测试。
如有侵权，或需要完整代码，请及时联系博主。