Samd11 USB serial

Other Hardware 3rd Party Boards
1

Hello All,
i am using custom board based on samd11d14. It is powered by USB.
I am using USB CDC library from Mattiartech.

It is working, but i observe something strange.
When PC goes in sleep, obviously the usb connection stop. And maybe samd11 start working incorectly...
When PC wake up, connection didnt restore automatically, and i have to reboot PC, so my CDC connection start working again.

is there any good way after PC wake up to reboot samd11 and usb connection automatically?
In the setup i have this code:

void setup() {
  //   // put your setup code here, to run once:
  Serial.begin(9600);
  Serial.setTimeout(10);
  while (!Serial);```

i put this code in loop, but don't know if it will work

void loop()
{

if(!Serial && digitalRead(VBUS)==1) {NVIC_SystemReset();} // processor software reset

2

I have USB Vbus connected on PA27, maybe i could observe this and make software reset on Rising edge?

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3

So you wanna try triggering on Vcc from a USB-port? If the computer only goes into sleep it could be the case that Vcc will still be there.

Maybe you could try some kind of handshake with a timeout, so your board recognizes a lost connection and restarts.

4

Yes, and there is yet no good way to restart the USB Serial connection after sleep. I've tried various libraries (Adafruit has the best, I think) but none of them worked reliably in my tests.

Deep sleep and USB Serial on the SAMD are not yet compatible, so use an alternative hardware serial port instead, which will survive deep sleep. A Serial1 definition is built in the the Adafruit core and it is easy to define others.

5

Hi @sukhoi

Unfortunately native USB requires the host computer to reestablish the connection to the microcontroller. The console on the Arduino IDE version 1 does reconnect, but requires the somewhat unsatisfactory insertion of half second delay to get it working with the SAMD21:

// Program to test COM port receovery after sleep mode

void setup() 
{
  pinMode(A1, INPUT_PULLUP);                      // Intialise button input pin and activate internal pull-up resistor
  pinMode(LED_BUILTIN, OUTPUT);                   // Initialise the LED_BUILTIN output
  attachInterrupt(A1, dummyFunc, LOW);            // Activate a LOW level interrupt on the button pin
  NVMCTRL->CTRLB.bit.SLEEPPRM = NVMCTRL_CTRLB_SLEEPPRM_DISABLED_Val;    // Prevent the flash memory from powering down in sleep mode
  SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;              // Select standby sleep mode
  Serial.begin(115200);                           // Intialise the native USB port
  while (!Serial);                                // Wait for the console to open
}

void loop() 
{
  digitalWrite(LED_BUILTIN, LOW);                 // Turn off the LED
  Serial.println(F("Sleeping Zzzz...wait for button to wake"));  // Send sleep message to the console
  USBDevice.detach();                             // Detach the native USB port
  SysTick->CTRL &= ~SysTick_CTRL_TICKINT_Msk;     // Disable SysTick interrupts
  __DSB();                                        // Ensure remaining memory accesses are complete
  __WFI();                                        // Enter sleep mode and Wait For Interrupt (WFI)
  SysTick->CTRL |= SysTick_CTRL_TICKINT_Msk;      // Enable SysTick interrupts
  USBDevice.attach();                             // Re-attach the native USB port
  digitalWrite(LED_BUILTIN, HIGH);                // Turn on the LED
  delay(500);                                     // Wait for half a second (seems to be necessary to give time for the USB port to re-attach)
  while(!Serial);                                 // Wait for the console to re-open
  Serial.println();                               // Add a newline
  Serial.println(F("Button depress...waking up")); // Send a wake up message
  delay(500);                                     // Wait half a second
}

void dummyFunc() {}                               // Dummy interrupt service routine