#物联网征文# 系统服务- OpenHarmony 串口服务访问

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作者：邱云

项目介绍

本文档是在eTS项目hap包中实现串口访问的使用说明，通过JS接口开放给上层应用使用。

一、开发环境准备

安装OpenHarmony SDK

1. 在DevEco Studio菜单栏选择Tools->SDK Manager

2. OpenHarmony SDK选项中选择配备API版本进行安装

二、创建eTS项目

创建支持Native C++的eTS项目

三、NAPI库相关

生成串口NAPI库

1. 添加文件src/main/cpp/types/libserialhelper/serialhelper.d.ts

/*
 * Copyright (C) 2021-2022 Huawei Device Co., Ltd.
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import AsyncCallback, Callback from "basic";
declare namespace serialHelper 
  /**
   * Open serial port.
   * @param dev Indicates the serial port dev.
   */
  function openSerial(dev:string, callback: AsyncCallback<void>): void;
  function openSerial(dev:string): Promise<void>;

  /**
   * Close serial port.
   * @param dev Indicates the serial port dev.
   */
  function closeSerial(dev:string, callback: AsyncCallback<void>): void;
  function closeSerial(dev:string): Promise<void>;

export default serialHelper;

2. 添加文件src/main/cpp/types/libserialhelper/package.json


  "name": "libserialhelper.so",
  "types": "./serialhelper.d.ts"

3. 根据serialhelper.d.ts文件生成对应的c++源码

方式一：手动编写src/main/cpp/serial_helper.cpp

```c++
struct AsyncCallInfo
napi_env env = nullptr;
napi_ref callbackRef = nullptr;
napi_deferred deferred = nullptr;
napi_async_work work = nullptr;
void data = nullptr;
;
static void AsyncCallFinish(AsyncCallInfo asyncCallInfo, int32_t result, napi_value *asyncResult)

if (asyncCallInfo->deferred)
if (result == 0)
napi_resolve_deferred(asyncCallInfo->env, asyncCallInfo->deferred,
asyncResult[1]==nullptr?asyncResult[0]:asyncResult[1]);
else
napi_reject_deferred(asyncCallInfo->env, asyncCallInfo->deferred, asyncResult[0]);

else
napi_value callback = nullptr;
napi_get_reference_value(asyncCallInfo->env, asyncCallInfo->callbackRef, &callback);
napi_call_function(asyncCallInfo->env, nullptr, callback, CALLBACK_ARGV_CNT, asyncResult, nullptr);
napi_delete_reference(asyncCallInfo->env, asyncCallInfo->callbackRef);


```c++
static napi_value Call_OpenSerial(napi_env env, napi_callback_info info)

    size_t argc = 0;
    napi_value args[DEFAULT_ARG_COUNT] = 0;
    napi_get_cb_info(env, info, &argc, args , nullptr, nullptr);
    ...
    napi_value resourceName = nullptr;
    napi_create_string_utf8(env, "x_napi_tool", NAPI_AUTO_LENGTH, &resourceName);
    napi_create_async_work(env, nullptr, resourceName,
            [](napi_env env, void* data) 
                AsyncCallInfo* asyncCallInfo = (AsyncCallInfo*)data;
                OpenSerialValue* openValue = (OpenSerialValue*)asyncCallInfo->data;
                //openValue->out = SerialClient::GetInstance()->OpenSerial(openValue->dev);
            ,
            [](napi_env env, napi_status status, void* data) 
                AsyncCallInfo* asyncCallInfo = (AsyncCallInfo*)data;
                OpenSerialValue* openValue = (OpenSerialValue*)asyncCallInfo->data;
                napi_value asyncResult[CALLBACK_ARGV_CNT]=nullptr, nullptr;
                napi_create_int32(env, openValue->out, &asyncResult[0]);
                AsyncCallFinish(asyncCallInfo, openValue->out,asyncResult);
                napi_delete_async_work(env, asyncCallInfo->work);
                delete openValue;
                delete asyncCallInfo;
            ,
            (void*)asyncCallInfo, &asyncCallInfo->work);
    napi_queue_async_work(env, asyncCallInfo->work);
    return retValue;

方式二：使用NAPI框架生成工具生成 工具链接

1）将serialhelper.d.ts、basic.d.ts复制到同一目录中，创建out目录

2）执行./napi_generator-linux -f serialhelper.d.ts -o out

3）将生成的源码文件复制到src/main/cpp

4. make文件：src/main/cpp/CMakeList.txt

# the minimum version of CMake.
cmake_minimum_required(VERSION 3.4.1)
project(XComponent)

set(NATIVERENDER_ROOT_PATH $CMAKE_CURRENT_SOURCE_DIR)

include_directories($NATIVERENDER_ROOT_PATH)
add_library(serialhelper SHARED serial_helper.cpp)
target_link_libraries(serialhelper PUBLIC libace_napi.z.so libc++.a)

5. 添加项目依赖

entry/package.json

"devDependencies": 
    "@types/libserialhelper.so": "file:./src/main/cpp/types/libserialhelper"

entry/package-lock.json

"dependencies": 
   "@types/libserialhelper.so": 
      "version": "file:src/main/cpp/types/libserialhelper",
      "dev": true

6. 编译生成

修改编译项entry/build-profile.json5：

"buildOption": 
  "externalNativeOptions": 
    "path": "./src/main/cpp/CMakeLists.txt",
    "arguments": "-v -DOHOS_STL=c++_shared",
    "abiFilters": [
      "armeabi-v7a",
    ],
    "cppFlags": "",

四、实现串口异步回调

添加串口IPC客户端libserialport_service_api.z.so库，并且实现具体的异步回调功能

  1. 将libserialport_service_api.z.so复制到entry/libs/armeabi-a7v目录

  2. 将库的头文件复制到entry/src/main/cpp/include目录

  3. 继承SerialCallbackBase类，实现串口数据异步回调SerialAsyncCallback

    ```c++
    class SerialAsyncCallback: public SerialCallbackBase
    public:
    SerialAsyncCallback() = default;
    ~SerialAsyncCallback();

    // 通知回调事件
    void OnCallBackEvent() override;
    // 接收到串口数据
    void OnRecvData(const uint8_t *buffer, uint32_t length) override;
    ...
    ;

  4. 修改src/main/cpp/CMakeList.txt文件

    # the minimum version of CMake.
cmake_minimum_required(VERSION 3.4.1)
project(XComponent)

set(NATIVERENDER_ROOT_PATH $CMAKE_CURRENT_SOURCE_DIR)

include_directories($NATIVERENDER_ROOT_PATH
                   $NATIVERENDER_ROOT_PATH/include
                   )

link_directories($NATIVERENDER_ROOT_PATH/../../../libs/$CMAKE_OHOS_ARCH_ABI)
add_library(serialhelper SHARED serial_helper.cpp x_napi_tool.cpp serial_async_callback.cpp)
target_link_libraries(serialhelper PUBLIC libace_napi.z.so libc++.a libhilog_ndk.z.so libuv.so libserialport_service_api.z.so)

  5. 在napi函数中调用api函数，使用NAPI框架生成工具生成OpenSerial代码，如下：

    ```c++
    struct OpenSerial_value_struct
    std::string in0;
    int32_t out;
    ;

    void OpenSerial_execute(XNapiTool pxt, void data)

    OpenSerial_value_struct vio = (OpenSerial_value_struct )data;
    vio->out = get_serial_client()->OpenSerial(vio->in0);

    void OpenSerial_complete(XNapiTool pxt, void data)

    OpenSerial_value_struct vio = (OpenSerial_value_struct )data;
    napi_value result = nullptr;
    result = NUMBER_C_2_JS(pxt, Int32, vio->out);

    napi_value args[XNapiTool::ARGV_CNT] = result, nullptr;
    pxt->FinishAsync(vio->out, args);

    delete vio;

    napi_value OpenSerial_middle(napi_env env, napi_callback_info info)

    XNapiTool *pxt = std::make_unique<XNapiTool>(env, info).release();
    if (pxt->IsFailed())
    napi_value err = pxt->GetError();
    delete pxt;
    return err;

    struct OpenSerial_value_struct *vio = new OpenSerial_value_struct();
    pxt->SwapJs2CUtf8(pxt->GetArgv(0), vio->in0);
    napi_value result = pxt->StartAsync(OpenSerial_execute, vio, OpenSerial_complete,
    pxt->GetArgc() == 2 ? pxt->GetArgv(1) : nullptr);
    if (pxt->IsFailed())
    result = pxt->GetError();

    return result;

  6. 模块注册

    ```c++
    static napi_value init(napi_env env, napi_value exports)

    std::shared_ptr<XNapiTool> pxt = std::make_shared<XNapiTool>(env, exports);
    //js函数与C++函数映射
    pxt->DefineFunction("setOptions", OHOS::SerialPort::SetOptions_middle);
    pxt->DefineFunction("openSerial", OHOS::SerialPort::OpenSerial_middle);
    pxt->DefineFunction("closeSerial", OHOS::SerialPort::CloseSerial_middle);
    pxt->DefineFunction("clearBuffer", OHOS::SerialPort::ClearBuffer_middle);
    pxt->DefineFunction("sendData", OHOS::SerialPort::SendData_middle);
    pxt->DefineFunction("recvData", OHOS::SerialPort::RecvData_middle);
    pxt->DefineFunction("transmit", OHOS::SerialPort::Transmit_middle);
    pxt->DefineFunction("on", OHOS::SerialPort::on_middle);
    pxt->DefineFunction("off", OHOS::SerialPort::off_middle);
    pxt->DefineFunction("setGPIODirection", OHOS::SerialPort::setGPIODirection_middle);
    pxt->DefineFunction("setGPIOValue", OHOS::SerialPort::setGPIOValue_middle);
    pxt->DefineFunction("getGPIOValue", OHOS::SerialPort::getGPIOValue_middle);
    return exports;

    static napi_module g_serialHelper_Module =
    .nm_version = 1,
    .nm_flags = 0,
    .nm_filename = nullptr,
    .nm_register_func = init,
    .nm_modname = "serialhelper",
    .nm_priv = ((void )0),
    .reserved = (void     )0,
    ;

    extern "C" attribute((constructor)) void Register_serialHelper_Module(void)

    napi_module_register(&g_serialHelper_Module);

  7. eTS调用接口验证

    import serialHelper from "libserialhelper.so"
...
//打开串口this.tty /dev/ttyXRUSB0
serialHelper.openSerial(this.tty).then(()=>
 HiLog.i(TAG, "serial openSerial " + this.tty + " success")
 this.status = 开
).catch((error)=> 
 HiLog.i(TAG, "openSerial " + this.tty + " failed:" + error)
);
...
//设置为异步
serialHelper.on("/dev/ttyXRUSB0", (data) => 
 var dataString = "";
 for (var i = 0; i < data.length; i++) 
   dataString += String.fromCharCode(data[i]);
 
 HiLog.i(TAG, "ttyXRUSB0 len:" + data.length + " data:" + dataString);
)

    应用启动后点击"打开/dev/ttyXRUSB0"按钮查看输出日志，出现serialport_client与serial_service_impl标志，表示访问串口服务成功

项目完整源码地址

代码传送

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