如何在Node js中同步使用串行端口? [英] how can i use serial port Synchronously in Node js ?

问题描述

我在节点js中使用serialport模块，并执行类似的代码，但是发生了错误.

for(i=0; i<5; i++){
    a(i) ; 
}

function a(i){

    port = new serialport(port_name,{

         baudRate:9600 ,

         parser: new serialport.parsers.Readline('\n')
    });

    port.on('open',function(){
         port.write(port_command+'\n');
         data = port.read();
         console.log(i + data);
         port.close();
    });
}

但发生错误

"UnhandledPromiseRejectionWarning:错误资源暂时不可用，无法锁定端口"

"UnhandledPromiseRejectionWarning:未处理的诺言拒绝.此错误可能是由于在没有catch块的情况下抛出了异步函数而引起的，或者是因为拒绝了未经.catch()处理的诺言.

"DeprecationWarning:已弃用未处理的承诺拒绝.将来， 未处理的承诺拒绝将终止节点. js过程 一个非零的退出代码.

我希望它们按

的顺序运行

a(0)端口打开，写入，读取，关闭

a(1)端口打开，写入，读取，关闭

a(2)端口打开，写入，读取，关闭

a(3)端口打开，写入，读取，关闭

a(4)端口打开，写入，读取，关闭

我认为a(0)打开，a(1)打开，所以出错..我该如何解决这个问题?

解决方案

您可以从函数中返回一个在端口关闭时解析的promise:

 function ping(i){
   const port = new serialport(port_name,{
     baudRate:9600 ,
     parser: new serialport.parsers.Readline('\n')
   });

   port.on('open',function(){
     port.write(port_command+'\n');
     data = port.read();
     console.log(i + data);
     port.close();
  });

  return new Promise(resolve => port.on("close", resolve));
 }

现在您可以通过以下方式实现循环了:

 (async function loop() {
   for(let i = 0; i < 3; i++) {
     await ping(i);
   }
 })();

i use serialport module in node js , and execute the code like this, but error occurred.

for(i=0; i<5; i++){
    a(i) ; 
}

function a(i){

    port = new serialport(port_name,{

         baudRate:9600 ,

         parser: new serialport.parsers.Readline('\n')
    });

    port.on('open',function(){
         port.write(port_command+'\n');
         data = port.read();
         console.log(i + data);
         port.close();
    });
}

but error is occurred ,

"UnhandledPromiseRejectionWarning: Error Resource temporarily unavailable Cannnot lock port"

"UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). "

"DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node. js process with a non-zero exit code.

I want them to run in order like

a(0) port open , write , read , close

a(1) port open , write , read , close

a(2) port open , write , read , close

a(3) port open , write , read , close

a(4) port open , write , read , close

i think a(0) open, a(1) open so error .. how can i solve this problem?

解决方案

You could return a promise from the function that resolves when the port closes:

 function ping(i){
   const port = new serialport(port_name,{
     baudRate:9600 ,
     parser: new serialport.parsers.Readline('\n')
   });

   port.on('open',function(){
     port.write(port_command+'\n');
     data = port.read();
     console.log(i + data);
     port.close();
  });

  return new Promise(resolve => port.on("close", resolve));
 }

Now you can achieve your loop as:

 (async function loop() {
   for(let i = 0; i < 3; i++) {
     await ping(i);
   }
 })();

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