UART frame error handling

[sandeepmistry]

Inspired by #341.

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/samd/package_samd-b196_index.json

ℹ️ To test this build:

1. Open the Preferences of the Arduino IDE.
2. Add the Build URL above in the Additional Boards Manager URLs field, and click OK.
3. Open the Boards Manager (menu Tools->Board->Board Manager...)
4. Install Arduino SAMD core - Pull Request UART frame error handling #349
5. Select one of the boards under SAMD Pull Request UART frame error handling #349 in Tools->Board menu
6. Compile/Upload as usual

[sandeepmistry]

Tested with the following sketch from @cmaglie:

unsigned int baud = 4800;
unsigned int delta = 1000000 / baud;

void setup() {
  pinMode(6, OUTPUT);
  digitalWrite(6, HIGH);
  Serial.begin(9600);
  while (!Serial);
  Serial1.begin(baud);
  delay(100);

  Serial.println("Starting");
  for (int l=20; l<51; l++) {
    Serial.print(l);
    Serial.print(" ");
    frame(l);
    delay(1);
    send(0x66);
    send(0x88);
    delay(10);
    dump();
  }
}

void loop() {
}

void dump() {
  Serial.print("RX> ");
  while (Serial1.available()) {
    char c = Serial1.read();
    Serial.print((int)c, HEX);
    Serial.print(" ");
  }
  Serial.println();
}

void d() {
  delayMicroseconds(delta);
}

void send(byte data) {
  digitalWrite(6, LOW); // START
  d();
  digitalWrite(6, data & 0x01); // 1
  d();
  digitalWrite(6, data & 0x02); // 1
  d();
  digitalWrite(6, data & 0x04); // 1
  d();
  digitalWrite(6, data & 0x08); // 1
  d();
  digitalWrite(6, data & 0x10); // 1
  d();
  digitalWrite(6, data & 0x20); // 1
  d();
  digitalWrite(6, data & 0x40); // 1
  d();
  digitalWrite(6, data & 0x80); // 1
  d();
  digitalWrite(6, HIGH); // STOP
  d();
}

void frame(int l) {
  digitalWrite(6, LOW);
  for (int i=0; i<l; i++) d();
  digitalWrite(6, HIGH);
  d();
}