#物联网征文# 【系统服务】- OpenHarmony 串口服务访问 原创 精华

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

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

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);
    }
}
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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;
}
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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)
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5. 添加项目依赖

entry/package.json

"devDependencies": {
	"@types/libserialhelper.so": "file:./src/main/cpp/types/libserialhelper"
}
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entry/package-lock.json

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

   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;
       ...
   };
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   复制

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)
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   复制

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：

   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;
   }
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   复制

6. 模块注册

   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);
   }
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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);
   })
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   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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