default serial/USB speed

[belebog]

I'm using an ESP32 WROOM32 board with Arduino IDE 2.3.6
Board package is 3.3.0 esp32 by espressif systems

On my first sketch, the first line in setup() i wrote is Serial.begin(115200);
The serial monitor of the ide is also set to 115200 baud, and communication between the two worked.

However, when i tried to extend my sketch (adding an SD card reader, and other peripherals), i occasionally got garbage before the first output of my first Serial.print() statement.
I wonder what that might have been - a kernel error message? and at what baud rate?
Should't the default speed for the kernel also be 115200 baud?

In <user>\AppData\Local\arduino\sketches\XXXXXXXXXXXX i found the file "sdkconfig" with an entry
CONFIG_ESP_CONSOLE_UART_BAUDRATE=115200

but also an entry of
"-DARDUINO_FQBN=\"esp32:esp32:esp32:UploadSpeed=921600,CPUFreq=240,FlashFreq=80,FlashMode=qio,FlashSize=4M,PartitionScheme=default,DebugLevel=none,PSRAM=disabled,LoopCore=1,EventsCore=1,EraseFlash=none,JTAGAdapter=default,ZigbeeMode=default\"",
in a file called "compile_commands.json"

[RandomInternetGuy]

The boot monitor runs at 115200. If you attach a receiver at that, you'll get all the chatter from boot rom and usually not miss a byte as the system progresses through the boot stages and into your code.

Electronics in general often do some glitchy things when powered up or rebooting, so it's not uncommon for some noise on the pins to be interpreted as a serial character (or multiples thereof). If you're expecting high-fidelity transfers, you should have an error detecting and correcting protocol that synchronizes early and discards any noise while estabilishing comms.



Your protocol analyzer should help you identify any stray data as an unexpected speed or noise.