The one with the wires soldered directly to the board stays here, meanwhile the other will be sent along to my collaborator. Together we'll finish filling out the keycode map, and tune this to be a light, easy-to-understand, easy-to-mod Sun keyboard platform.

static byte keyStack[6];
//TODO handle stack overflow
byte addToKeyStack( char key ){
  for( int i = 0; i < 6; i++ ){
    if( keyStack[i] == 0 ){
      keyStack[i] = key;
      return 1;
    }
  }
  return 0;
}
//TODO handle mismatched character
byte dropFromKeyStack( char key ){
  for( int i = 0; i < 6; i++ ){
    if( keyStack[i] == key ){
      keyStack[i] = 0;
      return 1;
    }
  }
  return 0;
}
//TODO add keyboard beeper test code
//TODO add keyboard beeper code to respond to exceptions
void setup(){
  SerialUSB.begin( 9600 );
  while( !SerialUSB );
  Serial1.begin( 1200 );
}

void loop(){
  while( Serial1.available() > 0 ){
    byte in = Serial1.read();
    static byte mod = 0;
    SerialUSB.println( in );
    switch( in ){
      case 76:
        mod |= MODIFIERKEY_CTRL;
        break;
      case 204:
        mod &= ~MODIFIERKEY_CTRL;
        break;
      case 102:
        addToKeyStack( KEY_C );
        break;
      case 230:
        dropFromKeyStack( KEY_C );
        break;
    }
    Keyboard.set_modifier( mod );
    Keyboard.set_key1( keyStack[0] );
    Keyboard.set_key2( keyStack[1] );
    Keyboard.set_key3( keyStack[2] );
    Keyboard.set_key4( keyStack[3] );
    Keyboard.set_key5( keyStack[4] );
    Keyboard.set_key6( keyStack[5] );
    Keyboard.send_now();
  }
}