This functionality is already available. @Jason2866 could you please help with PIO instructions?

Might using "-DARDUINO_USB_CDC_ON_BOOT=1" have unexpected consequences or implications?

My new config is essentially identical to the esp32-s2-saola-1.json that I was using before, with only that flag added. However, with the old device config everything works as expected, and with the new device config I'm unable to connect to an MQTT broker as expected... just stops there... my logging is...

Running task__handleReporting
WIFI: About to connect
FIRMWARE: Version 2
Available Ram: 103256 bytes
WIFI: Status: 3
WIFI: Connecting...
WIFI: CONNECTED
MQTT: About to connect

...and I get nothing more than that even with this in place:

build_flags = 
 -DCORE_DEBUG_LEVEL=5

Immediately after that last log I'm running...

 if (!m_mqttClient.connected()) {
 Serial.println("MQTT: Setting server");
 m_mqttClient.setServer(MQTT_BROKER, MQTT_PORT);
 Serial.println("MQTT: Setting callback");
 ...

I'm using knolleary/PubSubClient@^2.8 for MQTT, in case that's helpful.

Again, rolling back to a plain esp32-s2-saola-1 build works perfectly.

Any thoughts would be appreciated! :)

@papakpmartin Mhh, the mqtt issue is strange and cant explain.
You can try our modified mqtt pubsubclient version. Working for all esp

https://github.com/arendst/Tasmota/tree/development/lib/default/pubsubclient-2.8.13

Have seen this too:

WARNING: ESP32-S2FH4 (revision v0.0) chip was placed into download mode using GPIO0.
esptool.py can not exit the download mode over USB. To run the app, reset the chip manually.

Maybe adding this helps

 "use_1200bps_touch": true,
 "wait_for_upload_port": true,
 "require_upload_port": true,

Finally you can try:

Modified (forked) Platformio platform-espressif32 and changed to make this settings possible in boards.json

 "require_upload_port": true,
 "before_reset": "usb_reset",
 "after_reset": "no_reset",
 "speed": 460800

You can try if it works for you. If yes i will provide a PR currently we use this change only for project Tasmota

platform = https://github.com/tasmota/platform-espressif32/releases/download/2023.02.00/platform-espressif32.zip

Well, I was able to give this a go... it was weird. It mostly did not make a difference. Same symptom of starting nicely (as long as USB was plugged in and Monitor window was open) and running until approximately the same point, then pause for about 8-10 seconds, then crash/restart the ESP. No stacktrace.

My device file is basically...

{
 "build": {
 "arduino":{
 "ldscript": "esp32s2_out.ld"
 },
 "core": "esp32",
 "extra_flags": [
 "-DARDUINO_ESP32S2_DEV",
 "-DARDUINO_USB_CDC_ON_BOOT=1"
 ],
 "f_cpu": "240000000L",
 "f_flash": "80000000L",
 "flash_mode": "qio",
 "mcu": "esp32s2",
 "variant": "esp32s2"
 },
 "connectivity": [
 "wifi"
 ],
 "debug": {
 "openocd_target": "esp32s2.cfg"
 },
 "frameworks": [
 "arduino",
 "espidf"
 ],
 "name": "My Custom ESP32-S2",
 "upload": {
 "flash_size": "4MB",
 "maximum_ram_size": 327680,
 "maximum_size": 4194304,
 "speed": 460800,
 "use_1200bps_touch": true,
 "wait_for_upload_port": true,
 "require_upload_port": true
 },
 "url": "...",
 "vendor": "..."
 }

...and my platformio.ini contains basically...

[env:my-custom-esp32s2]
; platform = espressif32
platform = https://github.com/tasmota/platform-espressif32/releases/download/2023.02.00/platform-espressif32.zip
board = my-custom-esp32s2
framework = arduino
monitor_speed = 460800
monitor_filters =
 esp32_exception_decoder
 log2file
lib_deps = 
 knolleary/PubSubClient@^2.8
 ; others
; build_flags = 
; -DCORE_DEBUG_LEVEL=5

Oddly, with that set up once in a while it worked perfectly for a few minutes, but would eventually revert back to the same behavior.

At one point I thought it was maybe xTaskCreatePinnedToCore as when I replaced the single call to that with...

 xTaskCreate(
 task__handleReporting,
 "task__handleReporting",
 25000,
 NULL, // parameters
 10, // priority, higher number is higher priority
 &taskHandle__handleReporting
 // CONFIG_ARDUINO_RUNNING_CORE // Wi-Fi tasks must run on same core and Arduino
 );

...it worked. But it did not reliably work.

Not sure what to say, but I wanted to at least share what happened when I tried.

@papakpmartin Thinking that the issue you see is caused from your sketch. We had a "funny" bug in mqtt lib which caused weird issues.

Well, I'm not sure what to make of this, but commenting out all of the Serial.p... lines in the library doing the MQTT connection allowed everything to work as expected! But these debug lines from the library just before the MQTT stuff did work prior to me commenting everything out:

WIFI: Status: 3
WIFI: Connecting...
WIFI: CONNECTED

So essentially, all Serial lines in Comms.c here were commented out. However, unlike that example project, I have other libraries that do use Serial just fine... in setup() anyway.

Weird. But thought I'd share as it seemed interesting. :)

The issue was indeed my code. Having fixed that, this USB debug logging works wonderfully.

The problem was this while having no delay:

 while (!m_mqttClient.connect(mac_address.c_str(), MQTT_USER, MQTT_PASS)) {
 Serial.println("MQTT: Connecting...");
 Serial.print("MQTT: State: ");
 Serial.println(m_mqttClient.state());
 }

So in brief, @Jason2866's advice above worked perfectly.