SerialEvent not called?

Ignore this message... After a full day and night I realized what was going on...
Sorry for the noise.


I'm trying to program UDOO to exchange messages through serial port. I'm using serialEvent but something puzzling happens.
When I connect the external computer to the CN6 (J18 unplugged) the program works only from time to time (actually quite rarely). Most of the time I got the HB (hearth beat) signal on the console but nothing else. Sometime I can enter the serialEvent (I see the message back on the console), but the program does not enter the while loop there. Same thing seems to happen also when I plug J18 back and use serial monitor from the UDOO arm processor... This code (the attached one is a snippet) works perfectly on Arduino Uno.

Is there something I'm doing wrong with the jumpers, speed, whatever... Any advice would help greatly.

Code:

#include <circular_buffer.h>
 
int loopcount = 0;

void setup() {
  // initialize serial:
  Serial.begin(9600);
  delay(2000);
  Serial.write("Setup Completed\n");
}

circular_buffer incoming_buf;
circular_buffer outgoing_buf;

void serialEvent() {
  Serial.write("Something received\n");
  while (Serial.available()) {
    incoming_buf.insert(Serial.read());
  }
}

void send_msg() {
  char c = outgoing_buf.extract();
  while ( (c != '\n') && (c <= 127) && !outgoing_buf.empty()) {
    Serial.write(c);
    c = outgoing_buf.extract();
  }
  Serial.write('\n');
}


void loop() {
  loopcount = loopcount+1;
  if (loopcount == 500000) {
    Serial.write("HB\n");
    loopcount=0;
  }

  if (incoming_buf.messages()) {
    Serial.write("Received something\n");
    char c = incoming_buf.extract();
    int channel;
    switch (c) {
    case test_msg:
      Serial.write("Ok!");
      break;
    case '\n':
      break;
    default:
        signal_error(7);
      break;
    }
  }
}