Some bytes get lost by Serial.read() sometimes.

Projects Programming
1

Hello, I have just debugged a very frustrating bug in a larger project. I'll try to explain this in such a way that you guys don't have to read through hundreds of lines of irrelivant code. So here's the extent to which I've been able to isolate it.
I'm sending the possition of the cursor to the arduino. Sometimes one byte is lost, and the whole protocol gets borked. This only happens, if the DEBUG is pressent in the following function(if I comment it out, then the bytes get lost when I move the cursor fast):

void loop(){
   charicter = nextChar();
   #if DEBUG
        Serial.print("Idle mode, handling char:");Serial.println(String(charicter));
   #endif
   switch(charicter){
        case  3:set_cursor_pos();break;
  }
}

Here is the larger code.

/*
Scratch file.
*/
#define DEBUG 1
int x;
int y;
byte charicter;
int buffer_rows = 1;
int buffer_columns =100;
byte buffer[800];

#define dotCount 6
const int dotPins[] = {13,11,9,7,5,3};

void fill_buffer()
{
    for(int i = 0;i<buffer_columns;i++)
    {
        buffer[i]=1;
    }
}

void setup()
{
  // initialize the serial communication:
  Serial.begin(9600);
// initialize the the pins as outputs:
  for(int n = 0;n<dotCount;n++)
  {
    pinMode(dotPins[n], OUTPUT);
  }
  fill_buffer();
  Serial.println("FCHAD");
}

void displayChar(byte charicter)
{
  #if DEBUG
  Serial.print("Displaying charicter:");Serial.println(charicter);
  #endif  
  for(int n = 0;n<dotCount;n++)
  {
   if((1 << n) & charicter)
   {
     digitalWrite(dotPins[n],HIGH);
   }else
   {
     digitalWrite(dotPins[n+8],LOW);
   }
  }
}

boolean in_buffer(){
    return x<buffer_columns&&y<buffer_rows;
}

int readInt(){
    while(!Serial.available());//Block untill next char is here.
    int b1 = (uint16_t)Serial.read()<<8;
    while(!Serial.available());//Block untill next char is here.
    int b2 = Serial.read();
    return b1+b2;
}

byte nextChar()
{
  while(!Serial.available());//Block untill next char is here.
  return Serial.read();
}


void set_cursor_pos(){
    x=readInt();
    y=readInt();
    #if DEBUG
    Serial.print("CURSOR POSSITION SET TO:");Serial.print(String(x));
                                             Serial.print(",");
                                             Serial.println(String(y));
    #endif
    if(in_buffer())
        displayChar(buffer[x+y*buffer_columns]);
    else{x=0;y=0;
        #if DEBUG
        Serial.println("CURSOR ROUTED TO INVALID REGION WITHIN BUFFER.");
        #endif
    }
}

void loop(){
   charicter = nextChar();
   #if DEBUG
        Serial.print("Idle mode, handling char:");Serial.println(String(charicter));
   #endif
   switch(charicter){
        case  3:set_cursor_pos();break;
  }
}
//EOF

Should I try to debug this further and report a bug to the Arduino team? Or should I just leave it at that, and not use debugging code?

2

Is this a programming failure or a protocol failure?

int readInt(){
    while(!Serial.available());//Block untill next char is here.
    int b1 = (uint16_t)Serial.read()<<8;
    while(!Serial.available());//Block untill next char is here.
    int b2 = Serial.read();
    return b1+b2;
}

byte nextChar()
{
  while(!Serial.available());//Block untill next char is here.
  return Serial.read();
}

Why bother repeating the code in "nextChar" in "readInt"?

Serial.print("Idle mode, handling char:");

How long to print that string vs. the time before the next character becomes available?

IDE version?

3

Is the char really missing or is it a non-printable character like CR LF or BELL ?

try this:

void loop()
{
   charicter = nextChar();
   Serial.print("Idle mode, handling char:"); Serial.println(String(charicter));
   Serial.print("In hexadecimal :"); Serial.println(charicter, HEX);
   switch(charicter)
   {
        case  3: set_cursor_pos(); break;
   }
}

furthermore some coding remarks...

boolean in_buffer(){
    return x<buffer_columns&&y<buffer_rows;
}

is this also true for negative values of X and Y ?
or should it be:

boolean in_buffer()
{
    return (0 <= x && x < buffer_columns && 0 <= y && y < buffer_rows);
}

easier to read ...

int readInt()
{
    while (Serial.available() < 2);//Block untill next char is here.
    int val = (uint16_t)Serial.read()<<8 + Serial.read();
    return val;
}

don't do String(x)

Serial.print("Cursor X, Y: ");
Serial.print(x); 
Serial.print(",");
Serial.println(y);