Serial is freezing arduino

Question

I'm using a LinkIt ONE Arduino-like to send sensor data via MQTT.

It always worked very well, then out of the blue, it stopped printing anything using Serial.print();

But if I ommit the "Serial.begin(9600);" line, the code runs normally, sending sensor data via MQTT, even if I can't see debug output.

This shows the problem is on the Serial handling.

Since I can't show the entire code here, here's two test cases:

1.

void setup(){
  Serial.begin(9600);
  Serial1.begin(9600);
  while(!Serial); //Wait until Serial is ready before printing
}

void loop() {      
  Serial1.println("This came from serial 1"); //does nothing
  Serial.println("This came from serial 0");  //works
  delay(1000);
}

It shows me the following output:

This came from serial 0

This came from serial 0

Thi

Looks like the module freezes before the third iteration.

But if I omit the lines that aren't printed, from Serial1:

2.

void setup(){
  Serial.begin(9600);
  while(!Serial);  //Wait until Serial is ready before printing
}

void loop() {
  Serial.println("This came from serial 0");  //works
  delay(1000);
}

No output is shown on Serial monitor.

What is the reason behind this? Since Serial1 prints nothing, why can't I remove it?

Observations:

I tested the code in two LinkIt ONE modules of the same model.

I tested it in Arduino SDK 1.6.8, 1.5.6r2 and 1.6.5.

Edit:

Just made another test using the code below. It blinked two times showing that

Serial.begin(9600); runs

while(!Serial); runs (it didn't freeze the module waiting for Serial to initialize)

But Serial.println(); freezes

void setup(){
  pinMode(13, OUTPUT);
  blink();
  Serial.begin(9600);
  blink();
  while(!Serial); //Wait until Serial is ready before printing
}

void loop() {      
  Serial.println("This came from serial 0");  //works
  blink();
  delay(1000);
}

void blink(){
  digitalWrite(13, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(13, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);
}

Answer 1

The problem was solved by:

• making a clean install of Arduino IDE 1.6.9
• uploading the LinkIt SDK on board manager from version 1.1.17 to 1.1.23.

Then the Serial function returned back to normal.

Answer 2

I have bit similar problem. I thing, this is arduino bug. When start serial port, must be take out data from Rx. When read buffer overflow my arduino freeze. I can't run delay because when arduino wait, serial port can receive lot of data -> overflow -> freeze. Instead of delay I use own function wait(milis):

void wait(unsigned long wait_time){
  unsigned long start_time;
  start_time=millis();
  while ( millis() < (start_time+wait_time) ){
    if (serial.available() > 0) serial.read();
  }
}

Answer 3

This shows the problem is on the Serial handling.

The problem isn't actually in Serial, it's somewhere else. Many things are able to make the Arduino hang in mid-write. Show us the any code that you have written, plus links to the libraries you are using, and you'll have your answer in short order.

I will guess that you have a low-RAM condition, perhaps exacerbated by heap usage. Do you use String? I notice you're not using the F macro to save RAM.