Re: [External] : Re: data throttling under load when serial to usb adapter is used

[Johan Hovold <johan@kernel.org>]

On Mon, Dec 20, 2021 at 11:19:03AM +0100, Filip Žaludek wrote:

>   Yes, you are right! Such gadget hardware is without hw flow control.
>   I am using serial line only to capture console logs. I've tested
>   both commands also with sw flow control ixon, ixoff with similar
>   results.

The FTDI and PL2303 chips typically support automatic hardware flow
control, but you need to make sure the signals are wired up.

>   Hopefully somebody sitting on scarce big iron with both usb port and
>   serial port with proper hw flow control from this list gets
>   attracted to kindly re-test.

No need to retest anything. Just enable hardware flow control otherwise
there cannot be any guarantees.

> Interesting part for me is that only serial to usb direction is
> failing..

But in this case, it looks like your test script is just broken. You
kill the consumer before it has read all the data:

	uart_send__cat()
	{
	    cat < "$1" > /tmp/d16 &
	    RX_PID=$!
	    cat /tmp/d16_0 > "$2"
	    stty sane                           # better results
	    kill $RX_PID
	    wait $RX_PID
	    uart_info "$3"
	}

	...

	stty -F /dev/$SER 115200 raw -echo
	stty -F /dev/$USB 115200 raw -echo

	while true
	do
	    uart_send__cat /dev/$SER /dev/$USB "u->s"
	    uart_send__cat /dev/$USB /dev/$SER "s->u"
	done

Johan