Arduino program to recognize a usb c connection?

dlee99 · December 5, 2024, 6:12pm

I am trying to make my adafruit RP2040 which I program with the arduino framework to recognize it has a usb connected to it. Once it recognizes a usb then turn the tft display backlight off.

What I have so far works but I have to restart or reopen the serial monitor for it to work. Is there an other way to have the program know a usb is connected without having to restart the serial monitor?

bool usbConnected = false;
bool screenTurnedOff = false;

void setup(void)
{
  pinMode(10, OUTPUT); // display backlight pin
  Serial.begin(115200);
  delay(50);
}
void loop(void)
{
  while (Serial)
  {
    digitalWrite(10, LOW); // turn off backlight of screen
    usbConnected = true;
    screenTurnedOff = true;
    Serial << "USB connected" << endl;
    delay(2000);
  }
  if (usbConnected == true)
  {
    usbConnected = false;
    while (screenTurnedOff == true)
    {
      screenTurnedOff = false;
      digitalWrite(10, HIGH); // turn on backlight of screen
      Serial << "Turn screen back on." << endl;
    }
  }

maxgerhardt · December 5, 2024, 6:26pm

What core / platformio.ini are you working with? The ArduinoCore-mbed and Arduino-Pico core are different.

If you are using TinyUSB under the hood, there are more direct API functions that check if the computer (the USB host) has enumerated the device; So this will return true once the device is plugged into the computer, no serial monitor has to have been opened for that.

github.com

adafruit/Adafruit_TinyUSB_Arduino/blob/85476dcd8fb279c05ffe6aceace63d4292d45167/src/device/usbd.h#L85-L99


      
          // Check if device is connected (may not mounted/configured yet)

          // True if just got out of Bus Reset and received the very first data from host

          bool tud_connected(void);

          

          // Check if device is connected and configured

          bool tud_mounted(void);

          

          // Check if device is suspended

          bool tud_suspended(void);

          

          // Check if device is ready to transfer

          TU_ATTR_ALWAYS_INLINE static inline

          bool tud_ready(void) {

            return tud_mounted() && !tud_suspended();

          }

In Arduino-Pico, the if(Serial) check goes to the boolean operator, which goes to tud_cdc_connected()

github.com

earlephilhower/arduino-pico/blob/48bc91af36dc9e6be925575eb6603a23851c98a1/cores/rp2040/SerialUSB.cpp#L164-L172


      
          SerialUSB::operator bool() {
              CoreMutex m(&__usb_mutex, false);
              if (!_running || !m) {
                  return false;
              }
          
              tud_task();
              return tud_cdc_connected();
          }

which is in turn the logical AND of the general “is USB connected / ready” and “was the serial monitor connected”, as indicated by the virtual “DTR” line.

github.com

adafruit/Adafruit_TinyUSB_Arduino/blob/85476dcd8fb279c05ffe6aceace63d4292d45167/src/class/cdc/cdc_device.c#L132-L135


      
          bool tud_cdc_n_connected(uint8_t itf) {

            // DTR (bit 0) active  is considered as connected

            return tud_ready() && tu_bit_test(_cdcd_itf[itf].line_state, 0);

          }

dlee99 · December 5, 2024, 6:30pm

[env]
platform = https://github.com/maxgerhardt/platform-raspberrypi.git
platform_packages =
  framework-arduinopico@symlink://C:\Users\dlee\Documents\Dev\arduino-pico
framework = arduino
monitor_speed = 115200
board_build.core = earlephilhower
board_build.filesystem_size = 0.5m

[env:adafruit_feather]
;platform = raspberrypi
board = adafruit_feather
framework = arduino
lib_deps = 
	mikalhart/Streaming @ ^1.0.0

maxgerhardt · December 5, 2024, 6:33pm

As a quick test, can you check what the sketch

#include <Arduino.h>
extern "C" bool tud_connected(void);

void setup(void)
{
  pinMode(10, OUTPUT); // display backlight pin
  Serial.begin(115200);
  delay(50);
}
void loop(void)
{
  bool is_usb_connected = tud_connected(); // simple check
  if(is_usb_connected)
  {
    digitalWrite(10, LOW); // turn off backlight of screen
    if (Serial) { // just "connected" may not mean the serial monitor is open, so skip it.
      Serial << "USB connected" << endl;
	}
    delay(2000);
  } else {
     digitalWrite(10, HIGH); // turn on backlight of screen
  }
 }

is doing?

dlee99 · December 5, 2024, 6:47pm

I altered it a little with a red and blue LED so its easier to mess around with.

So far the red stays on even after I unplug the usb c.

#include <Streaming.h> // string calling
#include <Arduino.h>

extern "C" bool tud_connected(void);

void setup(void)
{
  pinMode(6, OUTPUT); // red led
  pinMode(7, OUTPUT); // blue led
  Serial.begin(115200);
  delay(50);
}
void loop(void)
{
  bool is_usb_connected = tud_connected(); // simple check
  if(is_usb_connected)
  {
    digitalWrite(6, HIGH);
    digitalWrite(7, LOW);
    if (Serial) { // just "connected" may not mean the serial monitor is open, so skip it.
      Serial << "USB connected" << endl;
	}
    delay(2000);
  } else {
     digitalWrite(6, LOW);
    digitalWrite(7, HIGH);
  }
 }

maxgerhardt · December 5, 2024, 6:57pm

Well, dang.

github.com

adafruit/Adafruit_TinyUSB_Arduino/blob/85476dcd8fb279c05ffe6aceace63d4292d45167/src/portable/raspberrypi/rp2040/dcd_rp2040.c#L41C1-L44C30


      
          // Current implementation force vbus detection as always present, causing device think it is always plugged into host.

          // Therefore it cannot detect disconnect event, mistaken it as suspend.

          // Note: won't work if change to 0 (for now)

          #define FORCE_VBUS_DETECT   1

I need to read up more on that… But that means that the “unplugged” event is never triggered which would cause it to go register as not connected again.

github.com

adafruit/Adafruit_TinyUSB_Arduino/blob/85476dcd8fb279c05ffe6aceace63d4292d45167/src/portable/raspberrypi/rp2040/dcd_rp2040.c#L306-L307


      
          // Disconnected

          dcd_event_bus_signal(0, DCD_EVENT_UNPLUGGED, true);

maxgerhardt · December 5, 2024, 6:59pm

Just FYI, the Raspberry Pi Pico board has a direct way to detect if the VUSB voltage is present or not, by measuring the GPIO24 pin. (schematics)

grafik

The Adafruit RP2040 in this regard is worse because it does not have that circuit, see here.

maxgerhardt · December 5, 2024, 7:04pm

Mhm, a generic idea: You do have direct access to the VBUS voltage on the header pins of the Adafruit RP2040.

That means you can Create the same 5.6K / 10K votlage divider as formed above by R10 and R1, and connect the middle to a free GPIO pin. Then yoa can just digitalRead() on that pin. If you have two resistors of the same ratio, you can recreate the circuit.

The voltage divider is just there to downconvert 5V into about 3.3V, or, 5V * 10K * (10K + 5.6K) = 3.2V, since the GPIOs can’t handle 5V.

dlee99 · December 5, 2024, 7:29pm

Interesting. Well that sucks. Thanks for looking into this on the platformIO side with me.

That is a lot more information compared to what I was able to find myself. The voltage divider is a good idea that you bought up for the adafruit feather.

Essentially I am testing the Adafruit Feather rp2040 first because I have designed a board where I was trying to do this with the display and usb. I have already made the board and have it on hand.

Although I do have this ESD chip right after the USB connector. And from that ESD chip it has D+ and D- and their associated test points which I measured were 3.3 volts when the USBC is connected to a power outlet. D+ and D- actually goes straight into the RP2040 pins 47 and 46. So I took D+ and D- to an open GPIO and read them as inputs. Unfortunately, the digital reading of D+ and D- didn’t always come up as consistent until some minutes later. So it was an unstable way to detect usb connection.

dlee99 · December 5, 2024, 8:11pm

BTW if I change like this it works. Instead of checking

extern "C" bool tud_connected(void);

I am now checking

extern "C" bool tud_suspended(void);
extern "C" bool tud_mounted(void);

// Test to detect usb connection on the adafruit feather rp2040

#include <Streaming.h> // string calling
#include <Arduino.h>

extern "C" bool tud_connected(void);
extern "C" bool tud_suspended(void);
extern "C" bool tud_mounted(void);

void setup(void)
{
    pinMode(6, OUTPUT); // red led
    pinMode(7, OUTPUT); // blue led
    Serial.begin(115200);
    delay(50);
}
void loop(void)
{
    bool is_usb_suspended = tud_suspended(); // simple check
    bool is_usb_mounted = tud_mounted();
    if (!is_usb_suspended && is_usb_mounted) // usb not suspended and is mounted
    {
        Serial << is_usb_suspended << endl;
        digitalWrite(6, HIGH);
        digitalWrite(7, LOW);
        Serial << "USB connected" << endl;
        delay(2000);
    }
    else
    {
        digitalWrite(6, LOW);
        digitalWrite(7, HIGH);
    }
}