UART loopback

I have a problem when I connect P9.24 (ttyO1.TX) with P9.26 (ttyO1.RX),
If I send data on serial port like this : echo 1 > /dev/ttyO1
And read data on serial port like this : cat /dev/ttyO1
The command output a lot of data indefinitely … and my ssh link doesn’t respond,
If I remove the jumper the system come back …
What wrong ?

Same problem with ttyO2,
Same problem with ttyO1 connected to ttyO2

I’m using kernel 3.8.13-bone69 (trying also 40 and 47) with debian 7.7,

I have the same problem too on the 3.18.1 kernel.

It can be fixed by initialising the port first, with something like:
stty -F /dev/ttyO1 raw clocal -crtscts -echo


The initial state for all ttys in Linux is ECHO.
When you setup loopback, you need to turn echo off.

stty -a -F /dev/ttyO1 will show you the current termios settings for the port.
See "man termios" for the manual on Linux terminal control.

Peter Hurley

I forgot this ...
I do this in my program

struct termios conf;
conf.c_lflag &= ~(ICANON | ECHO | ISIG);

Thank you very much.