Using socat for raw serial connection

Question

The goal is to connect to an embedded device using serial interface. So far, I've used:

stty -F /dev/ttyS2 115200 cs8 ixoff
socat readline,history=/etc/socat.history /dev/ttyS2,raw,echo=0

And it works excellent, but then I discovered that there are some options during system boot that require you to press a single key without pressing enter, and readline fails there. So my idea was to bind the ttyS2 to cons0, but then I discovered multiple problems, such as inability to quit (ctr+c, ctr+q ctr+] and even esc doesn't work), backspace and delete do not work, letters are typed twice, etc. So after some trial and error, I came up with this:

socat /dev/cons0,raw,echo=0,crnl /dev/ttyS2,raw,echo=0,escape=0x03,crnl

• raw on both sides allows a single key press to trigger a boot option
• echo=0 on both sides prevents key press doubling
• crnl on both sides prevent enter key press doubling
• escape=0x03 allows me to quit the thing by pressing ctr+c

The problem is, when I quit, my cons0 is all f****d up, as if it somehow preserved the raw,echo=0,crnl settings. I know this problem is probably too specific for my scenario, but I just need a simple way to send keystrokes to serial as I would with putty (which is not available on my platform). I am using socat because it is extremely lightweight, does not require any aditional libraries, and because the shown commands are a part of the greater script that uses expect.

Any ideas and suggestions are greatly appreciated.

Answer 1

As Austin Phillips says, you can use stty sane to recover...

...but what is even better is that you can (probably) append it to your socat command as socat xxxxx ; stty sane and have the recovery be automatic when you quit with ctrl-c.

Answer 2

Thanks, that worked for me! I just want to point out that the script should not rely on "static" console identification, because when expect spawns the script, it is going to have a completely different tty, therefor:

socat $(tty),raw,echo=0,escape=0x03 /dev/ttyS2,raw,echo=0,nonblock ; stty sane

edit: nonblock also solved the "enter" problem