USB baud rate

Question

How can I change the baud rate for the USB interface? Will serial:baudrate=9600 in the param.cfg file do it, or is that only for the TTL serial line?

Answer 1

As far as I understand it, the baudrate parameter on a USB interface has no effect. Data will still flow at 480 Mbps no matter what.

indeed serial:baudrate is for the hardware serial port

the corresponding param for serial-over-USB port would be usbserial:baudrate but again I believe changing this has no effect.

Answer 2

In general, the baud rate should be set by any app that uses the serial port. This is done with the SetCommState call, but of course the user interface varies from app to app.

None of this has anything to do with whether the serial port is built in, connected via USB, or something else.

Comments

Yes, you are right, this is how you set it (on Windows; you use an ioctl on Linux). But I still believe that this has no effect when doing serial over USB. You can set to 9600 bps but the USB data flow will still run at 480 Mbps, and I doubt that there is any kind of throttling mechanism in the kernel to reduce the number of USB packets that get sent over the 480 Mbps link so as to try to approximate an effective 9600 bps throughput. But I may be wrong as this is untested on our end.