【FFH】小熊派驱动调用流程（以调用LED灯驱动为例） 原创 精华

春节不停更，此文正在参加「星光计划-春节更帖活动」

一、流程总览

驱动调用的流程和纯代码开发的流程十分相似，本文着重点在于驱动调用的逻辑。

创建目录及相应源码文件–>编写驱动调用代码–>编写编译构建文件BUILD.gn–>编译烧录运行

二、源码目录结构

在./applications/BearPi/BearPi-HM_Micro/samples/目录下创建

my_led_app 源码目录

*my_led_app.c 驱动调用源码

*BUILD.gn 源码编译脚本

如图所示

三、编写驱动调用代码

在my_led_app.c中编写如下代码

#include <fcntl.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdio.h>
#include "hdf_sbuf.h"
#include "hdf_io_service_if.h"

#define LED_WRITE_READ 1
#define LED_SERVICE "hdf_led"

static int SendEvent(struct HdfIoService *serv, uint8_t eventData)
{
    int ret = 0;
    struct HdfSBuf *data = HdfSBufObtainDefaultSize();
    if (data == NULL)
    {
        printf("fail to obtain sbuf data!\r\n");
        return 1;
    }

    struct HdfSBuf *reply = HdfSBufObtainDefaultSize();
    if (reply == NULL)
    {
        printf("fail to obtain sbuf reply!\r\n");
        ret = HDF_DEV_ERR_NO_MEMORY;
        goto out;
    }
    /* 写入数据 */
    if (!HdfSbufWriteUint8(data, eventData))
    {
        printf("fail to write sbuf!\r\n");
        ret = HDF_FAILURE;
        goto out;
    }
    /* 通过Dispatch发送到驱动 */
    ret = serv->dispatcher->Dispatch(&serv->object, LED_WRITE_READ, data, reply);
    if (ret != HDF_SUCCESS)
    {
        printf("fail to send service call!\r\n");
        goto out;
    }

    int replyData = 0;
    /* 读取驱动的回复数据 */
    if (!HdfSbufReadInt32(reply, &replyData))
    {
        printf("fail to get service call reply!\r\n");
        ret = HDF_ERR_INVALID_OBJECT;
        goto out;
    }
    printf("\r\nGet reply is: %d\r\n", replyData);
out:
    HdfSBufRecycle(data);
    HdfSBufRecycle(reply);
    return ret;
}

int main(int argc, char **argv)
{
    int i;
    
    /* 获取服务 */
    struct HdfIoService *serv = HdfIoServiceBind(LED_SERVICE);
    if (serv == NULL)
    {
        printf("fail to get service %s!\r\n", LED_SERVICE);
        return HDF_FAILURE;
    }

    for (i=0; i < argc; i++)
    {
        printf("\r\nArgument %d is %s.\r\n", i, argv[i]);
    }

    SendEvent(serv, atoi(argv[1]));

    HdfIoServiceRecycle(serv);
    printf("exit");

    return HDF_SUCCESS;
}

这一部分是本文的重点部分

OpenHarmony的设备开发中的驱动调用与单片机的驱动开发不太相同，以往单片机的驱动调用往往是采用库函数调用的方式，但OpenHarmony的驱动调用采用的是驱动程序暴露出一个server，程序通过Dispatch发送指令的方式。有点类似与ROS的消息通信机制中的话题发布和订阅。在OpenHarmony中驱动调用的这部分程序属于用户程序，是用户态的内容，而驱动是内核态的内容。所以用户程序无法直接访问驱动，上面代码通过Dispatch向驱动程序发送指令从而实现LED灯的亮灭。

3.1 发送指令到驱动程序

我们看下my_led_app.c中SendEvent函数中通过Dispatch发送到驱动的代码

/* 通过Dispatch发送到驱动 */
    ret = serv->dispatcher->Dispatch(&serv->object, LED_WRITE_READ, data, reply);
    if (ret != HDF_SUCCESS)
    {
        printf("fail to send service call!\r\n");
        goto out;
    }

    int replyData = 0;

这段代码实现将指令发送到驱动程序

驱动程序指令接受的的代码在上一篇文章中的led.c驱动代码中的LedDriverDispatch函数

// Dispatch是用来处理用户态发下来的消息
int32_t LedDriverDispatch(struct HdfDeviceIoClient *client, int cmdCode, struct HdfSBuf *data, struct HdfSBuf *reply)
{
    uint8_t contrl;
    HDF_LOGE("Led driver dispatch");
    if (client == NULL || client->device == NULL)
    {
        HDF_LOGE("Led driver device is NULL");
        return HDF_ERR_INVALID_OBJECT;
    }

    switch (cmdCode)
    {
    /* 接收到用户态发来的LED_WRITE_READ命令 */
    case LED_WRITE_READ:
        /* 读取data里的数据，赋值给contrl */
        HdfSbufReadUint8(data,&contrl);                  
        switch (contrl)
        {
        /* 开灯 */
        case LED_ON:                                            
            GpioWrite(g_Stm32Mp1ILed.gpioNum, GPIO_VAL_LOW);
            status = 1;
            break;
        /* 关灯 */
        case LED_OFF:                                           
            GpioWrite(g_Stm32Mp1ILed.gpioNum, GPIO_VAL_HIGH);
            status = 0;
            break;
        /* 状态翻转 */
        case LED_TOGGLE:
            if(status == 0)
            {
                GpioWrite(g_Stm32Mp1ILed.gpioNum, GPIO_VAL_LOW);
                status = 1;
            }
            else
            {
                GpioWrite(g_Stm32Mp1ILed.gpioNum, GPIO_VAL_HIGH);
                status = 0;
            }                                        
            break;
        default:
            break;
        }
        /* 把LED的状态值写入reply, 可被带至用户程序 */
        if (!HdfSbufWriteInt32(reply, status))                
        {
            HDF_LOGE("replay is fail");
            return HDF_FAILURE;
        }
        break;
    default:
        break;
    }
    return HDF_SUCCESS;
}

3.2 从驱动程序接受数据

刚刚实现了用户态向内核态发送指令，同理，内核态也可以向用户态发送数据。

让我们看看驱动代码中向用户发送LED状态信息的代码（在led.c中LedDriverDispatch函数的一部分）

/* 把LED的状态值写入reply, 可被带至用户程序 */
        if (!HdfSbufWriteInt32(reply, status))                
        {
            HDF_LOGE("replay is fail");
            return HDF_FAILURE;
        }

下面是用户程序接收的部分

/* 读取驱动的回复数据 */
    if (!HdfSbufReadInt32(reply, &replyData))
    {
        printf("fail to get service call reply!\r\n");
        ret = HDF_ERR_INVALID_OBJECT;
        goto out;
    }
    printf("\r\nGet reply is: %d\r\n", replyData);

四、编写编译构建文件BUILD.gn

在BUILD.gn中添加以下代码

import("//build/lite/config/component/lite_component.gni")

HDF_FRAMEWORKS = "//drivers/framework"

executable("led_lib") {
    output_name = "my_led"
    sources = [
        "my_led_app.c",
    ]

    include_dirs = [
    "$HDF_FRAMEWORKS/ability/sbuf/include",
    "$HDF_FRAMEWORKS/core/shared/include",
    "$HDF_FRAMEWORKS/core/host/include",
    "$HDF_FRAMEWORKS/core/master/include",
    "$HDF_FRAMEWORKS/include/core",
    "$HDF_FRAMEWORKS/include/utils",
    "$HDF_FRAMEWORKS/utils/include",
    "$HDF_FRAMEWORKS/include/osal",
    "//drivers/adapter/uhdf/posix/include",
    "//third_party/bounds_checking_function/include",
    "//base/hiviewdfx/hilog_lite/interfaces/native/innerkits",
    ]

    deps = [
        "//base/hiviewdfx/hilog_lite/frameworks/featured:hilog_shared",
        "//drivers/adapter/uhdf/manager:hdf_core",
        "//drivers/adapter/uhdf/posix:hdf_posix_osal",
    ]
}

lite_component("my_led_app") {
    features = [
        ":led_lib",
    ]
}

五、编译烧录

参考之前文章Linux下配置小熊派-鸿蒙·叔设备开发（南向）的开发环境

六、运行

串口连接小熊派终端

./bin/my_led 0 #关闭LED
./bin/my_led 1 #开启LED
./bin/my_led 2 #翻转LED