Code to perform SLIP Protocol

Slip1.js 26 Aug 2016
A program to send and receive data packets in SLIP format.
Written for a PICO
https://en.wikipedia.org/wiki/Serial_Line_Internet_Protocol

//slip1.js
//26 Aug 2016
//Written on a PICO
//For testing connect Tx to RX for loopback, pins B6 and B7 Serial1

//SLIP protocol
// https://en.wikipedia.org/wiki/Serial_Line_Internet_Protocol
var END=0xC0;
var ESC=0xdb;
var ESC_END=0xdc;
var ESC_ESC=0xdd;

// END+Packet+END
//if the END byte occurs in the data to be sent, the two byte sequence
// ESC, ESC_END is sent instead,
//if the ESC byte occurs in the data, the two byte sequence ESC, ESC_ESC // is sent.

var baudrate=115200;
var Port=Serial1;
//Port.setup(baudrate);

function Packet(){
 this.A="";
}

var P=new Packet();

P.on('data',function(data){
 console.log("P.on= "+data);
});

//var sss="";
var State=0;

Port.on('data', function (data){
 var i;
 console.log("Port.on= "+data);
 for(i=0;i<data.length;i++){
  switch(State){
   case 0://looking for END to start packet
//console.log("0");
    if(data.charCodeAt(i)===END){
     State=10;
     i++;
    }
   return;
   case 10://get the packet
//console.log("10");
    if(data.charCodeAt(i)===END){
     State=0;
     P.emit('data',P.A);
     i++;
     return;
    }
    State=20;
   return;
   case 20://look for ESC
//console.log("20");
   if(data.charCodeAt(i)===ESC){State=30;i++;return;}
    P.A+=data.charAt(i);
    State=10;
   return;
   case 30://ESC was seen
//console.log("30");
    if(data.charCodeAt(i)===ESC_END){
     P.A+=String.fromCharCode(END);
     State=10;
     return;
    }
    if(data.charCodeAt(i)===ESC_ESC){
     P.A+=String.fromCharCode(ESC);
     State=10;
     return;
    }
   return;
   default:
    console.log("default error");
   break;
  }//end switch
 }//next i
});


function sendEND(){
 Port.write(String.fromCharCode(END));
}

function sendESC(){
 Port.write(String.fromCharCode(ESC));
}

function sendESC_END(){
 Port.write(String.fromCharCode(ESC_END));
}

function sendESC_ESC(){
 Port.write(String.fromCharCode(ESC_ESC));
}

function sendPacket(A){
 var i;
 sendEND();
  for(i=0;i<A.length;i++){
   switch(A.charCodeAt(i)){
    case END:
     sendESC();
     sendESC_END();
    break;
    case ESC:
     sendESC();
     sendESC_ESC();
    break;
    default:
     Port.write(A.charAt(i));
    break;
   }//end switch
  }//next i
 sendEND();
}

function test(){
 var text=
  "Hello"+String.fromCharCode(ESC)+"World"+String.fromCharCode(END)+
   "Eagles";
 Port.setup(baudrate);
 console.log("Text= "+text);
 sendPacket(text);
  
}//end test
test();

The output:

>echo(0);
Text= HelloÛWorldÀEagles
=undefined
Port.on= ÀHelloÛÝWorldÛÜEaglesÀ
P.on= HelloÛWorldÀEagles

1 Attachment

• slip1.js