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  • Author Author: oksbwn
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Arduino | Tutorial 3 | Serial Communication

oksbwn

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  • Former Member
    Former Member in reply to Jan Cumps

      Apparently, a reference to Serial in an if or while argument context evaluates to true if the specified serial port is available else there is a permanent/temporary error.  There must be something hidden in the compilation/interpreter that treats Serial special.  An if( Serial.isConnected() ) would be better.  Secrets are bad engineering practices but what can you do?  I cannot find any documentation of the static Serial object other than what's in the arduino.cc API.  Have you?

     

    To guard against a single spurious failure instance, I use this in setup() instead of the if-statement for Serial applications:

     

    int count_down = 3; 
    while( ! Serial ) {
          // Sleep 1 second if not yet ready.
          delay( 1000 );
          // Tried the maximum allowed times already?
          if( count_down-- < 1 ) {
               // Tried 3 seconds to get the serial connection ready - giving up.
               // Timeout error processing goes here
          }
    }
  • in reply to Jan Cumps

    : @richard_elkins is right. Actually I have only demonstrated how to use that. It's up to the user to put logic whatever he wants like he might reboot or he might stop execution or wait for certain time etc.

  • in reply to Former Member

    The compiler is a standard c++ compiler and the linker is also a known one. So whatever the Serial library does must be a c++ construct.

     

    The source for the System class is open, so we can have a look ourselves. Let's do that.

    The first who finds it is king for a day...

  • in reply to Former Member

    I have been digging in the source code.

     

    The files are available on github

     

    The one we're talking about is:

    https://github.com/arduino/Arduino/blob/master/hardware/arduino/avr/cores/arduino/HardwareSerial.h

     

    Relevant pieces of code

     

    class HardwareSerial : public Stream
{
// ...
  public:
    operator bool() { return true; }
// ...
}

// ... 
  extern HardwareSerial Serial;

     

     

    So it looks like the bool operator is indeed overridden for the class HardwareSerial (also checked SoftwareSerial, it's the same mechanism there), but it always returns true, whatever the state of the connection

  • Former Member
    Former Member in reply to Jan Cumps

    See the SerialEvent example at https://www.arduino.cc/en/Tutorial/SerialEvent

    Note that there are no include statements either for HardwareSerial.h nor SoftwareSerial.h.  In fact, there are no include statements at all.

    So, how is it that this "magical" Serial object is accounted for?

    There is not even an instantiation nor a constructor invoked by the user.

     

    It still looks to me that the Arduino IDE is adding something to the sketch before submitting it for C++ compilation.