Serial Baud Affects Nothing

Projects Programming
1

I'm using the SEEED XIAO, windows, and the Arduino IDE and Platform.IO. I am communicating with the board via ArduinoIDE and KiTTY.

Currently I just have a basic bit of code that starts up the serial port and prints an ADC value as quickly as possible. This was one of several tests I was doing to try to see how quickly I could get the XIAO to communicate. Basically bumping the baud rate higher and higher until things turn to mush.

However, I noticed that by the time I was setting the baud rate to 100,000,000, something clearly wasn't working. I discovered that the XIAO doesn't read the baud rate setting and does its own thing.

However, even the setting in Arduino or KiTTY affects nothing. I can try to read it at 1bps or 100,000,000bps. Nothing mismatches or breaks. It apparently is just ignoring any setting I use and deciding its own speed.....from both sides. This is kind of annoying, because I'm trying to build a PC interface and need all the bandwidth I can get, not what the chip assumes I need for simple debugging.

2

Boards with native USB don't use the baud rate as they don't use a UART. I have no idea at which speed you can transfer the data but that speed related to the USB speeds and is the speed you get.

You can select any baud rate in a terminal program or in your code and it will work. In my experience, non-matching baud rates between terminal and micro still work.

3

sterretje:
I have no idea at which speed you can transfer the data...

Datasheet:
SAM D21 USB peripheral supports both embedded host and device modes of operation, supporting full speed (12Mbits/s) and low speed (1.5Mbits/s) communication

Assuming the software on both sides is well written.

4

Quote from: Datasheet

:slight_smile:

I know, I could have looked it up.

5

The quote was intended solely to give @Jonathanese context. I did not mean it to be a slight. I apologize.

6

Thanks for the info, folks!

That really helps, and it makes sense.

Not sure how I'll be able to tell which baud rate it's using 1.5Mbit and 12Mbit are both pretty quick.

7

No worries, apologies not needed but accepted.

8

It's not using 1.5Mbit or 12 Mbit. It is somewhere in-between, and will depend on what other data is being transferred, and other factors. 12Mbit is the raw bit rate of USB1.0. Data will very rarely be transferred that fast, as there is always gaps between packets, and other interruptions. USB 1.0 typically struggles to maintain even 1Mbyte/sec, or ~8Mbit/sec, over any length of time. USB 2.0 will be MUCH faster, and USB 3.0 much faster still.

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