ESP32-S2 CDC doesn't show up after flashing in download mode

[UnexpectedMaker]

While in the beta branch, any S2 boards that were set to use CDC, that had a VID/PID, would appear in the ports list after initial (from being in download mode) and then manually reset. They would appear as the board name (eg: /dev/cu.usbmodem12345 (UM FeatherS2) - but this no longer works.

Once reset, the board doesn't appear at all in the post list and requires going back into download mode again to been seen and flashed again.

Tested on WIn 10 and macOS Catalina with both FeatherS2 and TinyS2 boards. I cant test using ESP32S2 Dev Board as that has no menu for CDC.

[pedrominatel]

Hi @UnexpectedMaker,

Is something similar you are trying to do? https://youtu.be/_I-MI8_gGM8?t=4189 (It's in Portuguese, sorry :( )
I was able to use it directly with CDC. I've tested with Ubuntu 20.04.

[UnexpectedMaker]

Hi @UnexpectedMaker,

Is something similar you are trying to do? https://youtu.be/_I-MI8_gGM8?t=4189 (It's in Portuguese, sorry :( )
I was able to use it directly with CDC. I've tested with Ubuntu 20.04.

I'm not really sure what that video is showing, sorry.

[UnexpectedMaker]

@me-no-dev @chegewara I've found the issue and how to reproduce it and why others are not seeing it:
https://www.dropbox.com/s/3as58ok0qzckri3/ESP32-S2-CDC-Issue-repo.mov?dl=0

If Serial.begin() is present, it works. If Serial.begin() is not present, then the CDC doesn't enumerate and teh user has to go into download mode to flash the board every time.

So I guess this is still linked to the previous issue about CDC and Serial, but for use cases where serial is not needed, the CDC should still enumerate as a device to flash to.

Thanks!

[chegewara]

Yes, it is exactly what i described in the other issue. Serial.begin() is mandatory to start USB, without it USB just send descriptors and thats it.

[UnexpectedMaker]

Yes, it is exactly what i described in the other issue. Serial.begin() is mandatory to start USB, without it USB just send descriptors and thats it.

Ok, sorry I created extra noise about it ;)

My focus was on no CDC enumerating and not that Serial wasn't working, so I was just focused on the enumeration/flashing side of the issue.

Do we have an idea about how to fix this? It used to work fine in the S2 beta - and as I mentioned in the video, there used to be another CDC option in the menu, one for which USB was being used, and one for which UART serial would output to.

[chegewara]

When you select Serial connected to: USB you have to call Serial.begin() to flash over USB next time. It is how it is.
It always was like that. That line of code is required to fully initialize USB CDC.

[UnexpectedMaker]

When you select Serial connected to: USB you have to call Serial.begin() to flash over USB next time. It is how it is.
It always was like that. That line of code is required to fully initialize USB CDC.

I don't agree - this is not how it used to work while in Beta. I was the one working with @me-no-dev on how this initial worked, and there wasn't even a "serial output goes to...." menu option when CDC support was first implemented.

It was possible back then to flash to the CDC and have it enumerate before we could even direct serial output to the CDC - that came after.

This is a BUG. This should 100% NOT work this way. As I said, there used to be 2 menu options. One has been removed. the one that allowed the user to decide if they were using the CDC or external Serial2UART.

If this is how it's intended to work, then it's a terrible implementation. It's not obvious or user friendly in any way.

To a user - having the CDC enumerate has nothing to do with having serial output enabled or not. Not every project uses serial out.

This workflow has to change.

[UnexpectedMaker]

Just to be clear... I should be able to connect a FeatherS2 to my computer, select I am using the CDC, flash an empty Arduino project onto it.. just an empty setup(){} and loop(){} and after I flash it and it restarts, it should appear in my ports list so I can flash it again and again, no matter what is in my firmware.

A user should not have to put any "required" code in their own firmware for CDC to kick in.

[UnexpectedMaker]

Here is a support request I had on my discord server today, one of many I have to deal with showing this exact issue and why this behaviour needs to be fixed. I have permission from the OP to post this....

[chegewara]

@me-no-dev

[me-no-dev]

what that user describes is expected. You do use a different serial for your boards so the enumerated serial will change.

1. puts manually the board into download mode
2. flashes the board, but since this is USB flash with manual enter into download mode, the chip can not reboot into the app on it's own
3. reboots manually into the app, but now the app starts the CDC with different serial (your feather s2 one) so the port address changes to some other /dev/cu.usbmodemXXXXXX

persistence or not, this will always be the case :)

[UnexpectedMaker]

what that user describes is expected. You do use a different serial for your boards so the enumerated serial will change.

1. puts manually the board into download mode
2. flashes the board, but since this is USB flash with manual enter into download mode, the chip can not reboot into the app on it's own
3. reboots manually into the app, but now the app starts the CDC with different serial (your feather s2 one) so the port address changes to some other /dev/cu.usbmodemXXXXXX

persistence or not, this will always be the case :)

Yup, I understand that (Though the ERROR:... is going to be changed to something less dramatic hopefully as it's not an error, but INFO for the user - espressif/esptool#631 )

But none of this addresses my issue and what I believe is a bug. The FeatherS2 in this case never presents itself as a new port unless the user has put Serial.begin() in their code.

If I choose the CDC, then it should enumerate and appear as a port no matter if I put Serial.begin() or not in my code. I've explicitly stated I am using the CDC, and therefor expect that the device appears for me after it restarts.

[igrr]

I guess we can call USBCDC::begin after USB::begin in

arduino-esp32/cores/esp32/main.cpp

Lines 50 to 52 in 21947eb

	#if ARDUINO_SERIAL_PORT //Serial used for USB CDC
	USB.begin();
	#endif

, maybe with a smaller default RX buffer size. It doesn't seem like a lot more code would be linked into the application if this is done, so the cost of starting CDC early is not too high.

Alternatively if the global change is not desirable, this can be made a board-specific thing, in one of two ways:

1. in main.cpp, add Serial.begin() guarded by ARDUINO_SERIAL_PORT == 1 && ARDUINO_AUTO_START_CDC, then define ARDUINO_AUTO_START_CDC macro for a specific board via boards.txt
2. provide board-specific initVariant function in https://github.com/espressif/arduino-esp32/tree/master/variants/um_feathers2, which would call Serial.begin if ARDUINO_SERIAL_PORT == 1. initVariant is called before setup, and any custom logic can be added there.

[UnexpectedMaker]

I guess we can call USBCDC::begin after USB::begin in

arduino-esp32/cores/esp32/main.cpp

Lines 50 to 52 in 21947eb

	#if ARDUINO_SERIAL_PORT //Serial used for USB CDC
	USB.begin();
	#endif

, maybe with a smaller default RX buffer size. It doesn't seem like a lot more code would be linked into the application if this is done, so the cost of starting CDC early is not too high.
Alternatively if the global change is not desirable, this can be made a board-specific thing, in one of two ways:

1. in main.cpp, add Serial.begin() guarded by ARDUINO_SERIAL_PORT == 1 && ARDUINO_AUTO_START_CDC, then define ARDUINO_AUTO_START_CDC macro for a specific board via boards.txt
2. provide board-specific initVariant function in https://github.com/espressif/arduino-esp32/tree/master/variants/um_feathers2, which would call Serial.begin if ARDUINO_SERIAL_PORT == 1. initVariant is called before setup, and any custom logic can be added there.

Hey Ivan :)

I can't think of any use case or situation where if I chose CDC from the menu that I would't want the USB to enumerate, so I think this should 100% be a global setting when using CDC, and not something at the board level.

Can you give me an example of a situation where a user might choose CDC but not want the CDC to actually enumerate to be used?