Serial.println（Serial.available（））; 改变Arduino代码的行为

Question

I have this piece of code on my Arduino:

These variables are defined as global, like this:

 #define arraySize 32        
 char inChar = '0';
 char inVariable[arraySize];
 byte index = 0;  
 byte inDigit;     
 int inNumber;

A function is defined like this:

void checkSeriale(){
     while(Serial.available() > 0){
       Serial.println(Serial.available());
       inChar = Serial.read();
        if(inChar != ':' && index < arraySize-1 && inChar != ';'){
           inVariable[index] = inChar;
           index++;
           inVariable[index] = '\0';
        }else{
           break;
        }
     }

     if(inChar == ':'){ 
       index = 0;
       while(Serial.available() >0 && index < 10 && inChar != ';'){
         inDigit = Serial.read() - '0';
         inNumber = inNumber * 10;
         inNumber = inNumber + inDigit; 
         index++; 
       }
       cambioVariabiliSeriale(inVariable);
     }

     if(inChar == ';'){
       cambioVariabiliSeriale(inVariable);
       inNumber=0;
       inChar='0';
       index=0;
     }
}

The checkSeriale() function loops in the Arduino loop() with some others functions that run some other pieces of code that do not affect any of these variables.

This function should get commands from the serial port in two forms:

1. variablename:variablevalue - This should change the the value of the variable called variablename to the new received value.
2. command; - This should simply run a external function to do something else.

The function reads the received data until it reaches a : or a ;

If it receives a : , it keeps on reading to get the value. The value is then stored in the inNumber variable and inVariable gets passed to a second function cambioVariabiliSeriale(String inVariable) that checks what variable name the inVariable string equals to and assigns inNumber to the variable that has the same name as inVariable .

The code as it is seems to work perfectly. Every received signal(with the right syntax) gets handled well.

But if I try and remove the Serial.println(Serial.available()); line, the code stops working. inNumber now always contains 0 .

I don't mind keeping that line in the code, but I think it is strange that executing that command keeps the code working.

Does someone know why that line affects the reading of the received value?

Answer 1

I've tried to run your code with some dummy values in (see below), and it seems to run ok with the line commented out, ie innumber does contain values. However after working through it I kinda sense I'm not understanding your logic. Is this roughly the flow:

1. check characters are in the serial receive buffer with Serial.available

2. If so, do one of three things:

a) if the char isn't a ';' or ':' or the last char in the array, add it to the inVariable array, increment the index counter and add a zero to the array

b) if the char is a ':', do a couple of checks and read the next char from the buffer as a number, then do something with that, then run cambioVariabiliSeriale

c) if the char is a ';', run cambioVariabiliSeriale and reset some indexes.

(Also, I don't think you need check if inChar != ';' when you're inside an if statement checked for inChar == ':')

Couldn't this be run as the following, so Serial.println(Serial.available()); can be commented out without effect?

void checkSeriale(){
  while(Serial.available() > 0){
    Serial.println(Serial.available());
    inChar = Serial.read();
    if(inChar != ':' && index < arraySize-1 && inChar != ';'){
      inVariable[index] = inChar;
      index++;
      inVariable[index] = '\0';
    }

    else if(inChar == ':'){ 
      index = 0;
      while(Serial.available() >0 && index < 10){
        inDigit = Serial.read() - '0';
        inNumber = inNumber * 10;
        inNumber = inNumber + inDigit; 
        index++; 
      }
      cambioVariabiliSeriale(inVariable);
    }

    else if if(inChar == ';'){
      cambioVariabiliSeriale(inVariable);
      inNumber=0;
      inChar='0';
      index=0;
    }
  }
}

I plugged a bunch of Serial Monitor prints into your original code to see what was going on - it's here if it's any use to you. Hope it helps!

#define arraySize 32        
char inChar = '0';
char inVariable[arraySize];
byte index = 0;  
byte inDigit;     
int inNumber;
int i; //counter

String repeatstring;

void setup(){
  Serial.begin(9600);
}

void loop(){
  checkSeriale();
}

void checkSeriale(){
  while(Serial.available() > 0){
    pr("Start of 'checkSeriale' function");
    pr("Characters available in serial receive buffer: " + String(Serial.available()));
    //Serial.println(Serial.available());
    inChar = Serial.read();
    pr("Read a char into InChar: " + String(inChar));
    pr("Characters available after Serial.read(): " + String(Serial.available()));
    if(inChar != ':' && index < arraySize-1 && inChar != ';'){
      pr("First 'if' statement (inChar not equal to colon)");
      inVariable[index] = inChar;
      index++;
      inVariable[index] = '\0';
      for(i=0;i<sizeof(inVariable);i++){
        Serial.print(String(inVariable[i]));
      }
    }
    else{
      pr("Else statement for first 'if', inChar equals colon hence break");
      break;
    }
  }
  if(inChar == ':'){ 
    pr("Second 'if' statement (InChar is equal to colon)");
    index = 0;
    pr("Characters available in serial receive buffer: " + String(Serial.available()));
    while(Serial.available() >0 && index < 10 && inChar != ';'){
      inDigit = Serial.read() - '0';
      pr("Characters available after Serial.read(): " + String(Serial.available()));
      pr("inDigit: " + String(inDigit));
      pr("inNumber: " + String(inNumber));
      inNumber = inNumber * 10;
      pr("inNumber * 10: " + String(inNumber));
      inNumber = inNumber + inDigit; 
      pr("InNumber + inDigit : " + String(inNumber));
      index++; 
    }
    cambioVariabiliSeriale(inVariable);
  }

  if(inChar == ';'){
    pr("third 'if' statement (inChar is equal to semicolon)");
    cambioVariabiliSeriale(inVariable);
    inNumber=0;
    inChar='0';
    index=0;
  }

}

void cambioVariabiliSeriale(char test[]){
}

//simple debug technique - use pr("something"); in your code - askchipbug
void pr(String txt){
  if(repeatstring != txt){
    //if the debug text is different, print it
    Serial.println(txt); //prints the text and adds a newline
    delay(1000); //just pauses the scrolling text for 1 second, make bigger if you want a longer pause
    repeatstring = txt;
  }
}