Add USB send timeout (take 2)

[sandeepmistry]

Replacement for #152.

This time I've used Paul Stoffregen's work on Teensy as inspiration.

The initial send timeout is 70ms, however if a send times out the next one will fail immediately if the previous write is not complete. A ZLP will be attempted to send if a timeout occurs, to detect the endpoint is ready to receive.

I've also removed the check for line state in Serial_::write. After opening the port the user or application can manually disable DTR or RTS.

[sandeepmistry]

Hi @RamonRibes,

Could you please add this to your testing list with the WiFi101 web server example, it's a replacement for #152. You should not see any delays with the web server now if you open and close the Serial monitor on Windows.

So far I've tested with my Mac running OS X 10.11.3 and a Windows 10 VM.

[RamonRibes]

Hi, @sandeepmistry,
I've been testing the following sketch with this patch, opening and closing serial monitor:

void setup() {
  Serial.begin(9600);
  Serial.println("hello");

  pinMode(6, OUTPUT);
}

void loop() {
  Serial.println("LED HIGH");
  digitalWrite(6, HIGH);
  delay(1000);

  Serial.println("LED LOW");
  digitalWrite(6, LOW);
  delay(1000);
}

...and is working as expected.
I will keep on using this patch since now on.
Regards.

[sandeepmistry]

@cmaglie @facchinm I've rebased this, so it's ready for review and testing.

[sandeepmistry]

@ArduinoBot is misbehaving a bit, however here's a new build:

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/samd/package_samd-b97_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 Add USB send timeout (take 2) #154
5. Select one of the boards under SAMD Pull Request Add USB send timeout (take 2) #154 in Tools->Board menu
6. Compile/Upload as usual

[cmaglie]

Working OK for me 👍
(tested on Linux and Windows 10)