ESP32-S3 USB CDC doesn't work on every computer, "serial port is closed" errors

[marcocipriani01]

Board

ESP32-S3-WROOM-1U

Device Description

Self-powered ESP32-S3-WROOM-1U custom board with USB connected on pins IO19 and IO20. The power comes from a barrel jack and a 3.3V LDO regulator.
There is a USB Type-C connector and a TVS diode array (designed for USB 2.0 usage). VUSB doesn't go anywhere except for the TVS diode.

Hardware Configuration

Version

v2.0.15

IDE Name

Arduino IDE

Operating System

Windows 10, 11

Flash frequency

QIO 80MHz

PSRAM enabled

no

Upload speed

921600, upload via native USB

Arduino settings

Just USB CDC on boot:

Description

In my company, we developed a product based on the ESP32-S3-WROOM-1U that uses USB CDC on a Type-C connector to communicate with the computer. During prototyping we didn't have major issues with USB, but now we're testing the first production batch of boards on a large sample of computers and in various conditions. Unfortunately, about ¼ of the PCs in our production test have trouble connecting to the ESP32-S3, and the issue is unclear to us. These are some of the behaviors we observed:

• On a few PCs, complete inability to connect to the serial port: every software we use to connect to the ESP32 says either "the serial port is closed" or simply "failed to connect". This includes the Arduino Serial Monitor, Visual Studio Code's Serial Monitor extension, our custom C# software and more.
  • No other info is provided by these software, and we're unable to debug the situation since we can't even connect once.
  • Putting the board in bootloader mode using GPIO0 correctly enters bootloader and these same PCs can successfully upload new sketches to the ESP32 using Arduino IDE.
• On other PCs, including my workstation, the issue only happens sporadically (probably ⅓ of the times). The rest of the times, everything works fine. Downgrading to the old arduino-esp32 core 2.0.12 seems to decrease the frequency of the issue on the affected PCs, but doesn't solve it.
• The rest of computers have absolutely no trouble connecting to the ESP32-S3 board under any circumstance. We can use our custom C# software to do all the things we need and USB never stops working,

While testing, I also discovered that opening and closing the serial monitor rapidly a few times (open-close-open-close-...) makes the USB CDC stop working. For example, I created a sketch that prints "Hello" and does one Serial.read() every second in the loop() function. After opening and closing the serial port a few times, I no longer see "Hello", I receive nothing.

The issues happens on all the 30 boards in our first production batch. They've been professionally reflow soldered by another company. I manually inspected all of them under a microscope for soldering defects around the USB Type-C connector and the ESP32 module. It is a 6 layer board and the USB differential pair is length-matched and impedance-controlled to 90Ω according to USB standard.

Sketch

Any Arduino sketch that uses Serial.print(), Serial.println(), Serial.read().

Debug Message

"The serial port is closed" on some software.

Other Steps to Reproduce

Unclear. Depends on the PC where testing.

I have checked existing issues, online documentation and the Troubleshooting Guide

• I confirm I have checked existing issues, online documentation and Troubleshooting guide.

[lbernstone]

Have you tested v3.0.0 and IDF to see if the behavior is the same?

[marcocipriani01]

Arduino-ESP32 v3.0.0 breaks our production firmware, I will try to make it work on v3 and let you know.

[Jason2866]

You can try latest version from branch https://github.com/espressif/arduino-esp32/tree/release/v2.x
HWCDC fixes/changes have been backported

[lbernstone]

Arduino-ESP32 v3.0.0 breaks our production firmware, I will try to make it work on v3 and let you know.

Well, then also check that a minimal sketch with the same hardware settings causes the issue. This seems like a core issue, not something in your code, but it will be useful to narrow that down.

[marcocipriani01]

I was able to upgrade to Arduino-ESP32 v3.0.0-RC1 and, while the situation is better, I'm still having a lot of trouble with USB on affected computers. In particular, on my current workstation, with Arduino-ESP32 v3, the following happens:

• Serial.begin() becomes stuck sometimes, i.e. blocks the microprocessor from continuing.
  • Since CDC on boot is enabled, Serial.begin() isn't actually needed, so I commented the line.
• The USB port seems to be in fact more reliable, improvements are clearly showing:
  • I no longer get the occasional error during an Arduino sketch upload that I used to get before (rare, but annoying). EDIT: see comment below
  • No more "the port is closed" errors
• Right after a new Arduino sketch upload, the USB CDC serial port works perfectly from every software, but just once:
  • Any further attempt to connect to the serial port does succeed (no errors), but no data is sent or received over the serial port. The ESP32 doesn't read or send anything.
  • This is especially bad if the serial monitor is set to send DTR and RTS signals. Otherwise, there is a small chance of the ESP32 working for another one or two connection attempts.

Here is an example screenshoot, taken from the Visual Studio Code Serial Monitor extension (by Microsoft). The ESP32 is programmed to echo any received string, which it doesn't after the first connection:

When this issue happens, Arduino IDE's serial monitor shows this, immediately after connection (and the ESP32 doesn't echo the strings, just like in VS Code):

Any suggestion or things I can try?

[marcocipriani01]

Now, for some reason, I can't even upload without setting the board in bootloader mode, and the echo sketch works only sometimes even after upload. COM7 exists in Device Manager and the Arduino Serial Monitor can connect to it.

[Jason2866]

Do you can provide a small example sketch where the problem arrives?

[marcocipriani01]

It's the one in the screenshoot:

void setup() {
  Serial.println("Boot!");
  // Comment or not?
  //Serial.begin(115200);
  Serial.print("Serial.begin() done.");
}

void loop() {
  if (Serial.available() > 0)
    Serial.print((char) Serial.read());
}

[Jason2866]

Setup is not as recommended, but this should not the reason.

void setup() {
  Serial.begin(115200);  
  Serial.println("Boot!");
  Serial.print("Serial.begin() done.");
}

void loop() {
  if (Serial.available() > 0)
    Serial.print((char) Serial.read());
}

[marcocipriani01]

Yes I know, but it doesn't matter. CDC on boot is enabled so Serial.begin() should do nothing, plus I even commented that line. Even if I leave setup() empty, the result is the same.
If Serial.begin() really does nothing, why did it halt my ESP32-S3 a few times?

[Jason2866]

Can you try this example https://github.com/espressif/arduino-esp32/blob/master/libraries/ESP32/examples/HWCDC_Events/HWCDC_Events.ino

It does as intended with my S3 CDC device. Tested with Mac. It could be a problem in combination with Windows.

[marcocipriani01]

Sure, I'll try it Monday when I go back to the office. May I ask what is the difference between using Serial (what I'm doing) and HWCDC HWCDCSerial (the example you linked)?

[Jason2866]

The way to use the HWCDC port as serial UART.