Investigate UART/CDC in all SoC

[SuGlider]

@SuGlider I've now tested ESP32 Arduino 2.0.3 with a number of ESP32 boards, using a benchmark that involves uploading a program of about 1400 characters to my uLisp interpreter and then running it. The results are as follows:

Board	Upload using UART	Upload using USB CDC	Benchmark
Adafruit Feather ESP32	OK	Not available	8.0 s
ESP32-S2-Soala-1	OK	Not available	5.7 s
Adafruit Feather ESP32-S2	Not available	OK	2.7 s
Adafruit QT-PY ESP32-S2	Not available	OK	2.7 s
Unexpected Maker Feather S2	Not available	OK	2.7 s
ESP32-S3-DevKitM-1	OK	Serial hangs up	6.1 s (USB)
ESP32-C3-DevKit1	OK	Not available	7.8 s
Adafruit QT-PY ESP32-C3	Not available	Serial hangs up	??

Key observations:

• Serial using UART works fine on all boards that support it.
• Serial using USB CDC works fine on ESP32-S2, fails on ESP32-S3 and ESP32-C3.
• Benchmark seems to run much slower if I've connected to the MCU via UART (eg 5.7s) compared to connecting to the same MCU via USB CDC (2.7s).

Any thoughts about why USB CDC is now OK on ESP32-S2 but not ESP32-S3 or ESP32-C3?

Also, any idea where there's such a difference in performance? My benchmark isn't making use of serial, except to print the result at the end.

Originally posted by @technoblogy in #6221 (comment)

[SuGlider]

@technoblogy
Let's continue it here.

[technoblogy]

Thanks.

[egnor]

probably unrelated? espressif/esp-idf#9318 (at a guess, that bug is user-app-specific, this bug is Arduino-runtime-specific)

[SuGlider]

Thanks @egnor for the reference. I'll take it into consideration for the S3 USB Serial JTAG interface.

[SuGlider]

@ALL

Examples about UART controlling are at PR #7412

[technoblogy]

Why is this closed? I have tested the ESP32-S3 CDC serial with Arduino core 3.1.0 and it still hangs up and so is unusable.