Re: Shell io from and to serial device

[Ben Klein <robobenklein@gmail.com>]

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I don't know if you have this available, but `timeout` is a common utility
program: https://manpages.ubuntu.com/manpages/cosmic/en/man1/timeout.1.html
(It's
GNU)

So you could start the whole grep pipeline with that command in a new
shell, or if you wanted you could do a callback to a parent ZSH process
like the zsh-async does with SIGWINCH, catch that and kill a job. (You
could enable job control then kill %0 or similar when you get the
interrupting signal back.)

On Wed, Feb 13, 2019 at 7:01 PM Dominik Vogt <dominik.vogt@gmx.de> wrote:

> Hi Folks,
>
> I'm really stuck with this problem.  We need a fast, and reliable
> way to send a string to a serial device and grep for a certain
> reply, and failed to make that work with "expect" - because its
> documentation is awful.  Anyway, it should be not too difficult to
> do with zsh.  The task is:
>
>   1. configure serial line, e.g. with
>
>     $ stty -F /dev/ttyUSB0 speed 115200 cs8 -cstopb -parenb -echo
>
>   2. Send some string to the serial line
>
>     $ echo foo > /dev/ttyUSB0
>
>   3. Grep for a certain reply with configurable, sub second timeout.
>
>     $ ??????
>
>   4. In case of a timeout, all input from the serial line is stored
>      in a file or shell variable.
>
> There should be no noticeable delay if the expected reply shows
> up immediately.
>
> Something like this should do it:
>
> -- snip --
> #!/usr/bin/zsh
>
> set -u
> set -C
>
> SEND="$1"
> EXPECT="$2"
> TIMEOUT="$3"
> DEV="$4"
> LOGFILE="$5"
> shift 5
>
> trap "exit 1" TERM
>
> # serial setup
> stty -F "$DEV" speed 115200 cs8 -cstopb -parenb -echo > /dev/null
> # watchdog process
> { sleep "$TIMEOUT"; echo "timeout" 1>&2; kill 0 2> /dev/null; } &
> # child sends string with delay
> { sleep 0.01; echo "$SEND" > "$DEV" } &
> rm -f "$LOGFILE"
> # parent waits for reply
> tee "$LOGFILE" < "$DEV" |
> while read LINE; do
>         if { cat <<EOF
> $LINE
> EOF
> } | grep -q "$EXPECT"
>         then
>                 trap : TERM
>                 kill 0 2> /dev/null
>                 exit 0
>         fi
> done
> exit 1
> -- snip --
>
> But this looks really complicated and the "sleep 0.01" is
> annoying.  There must be an easier way.
>
> Also, I'm not convinced that "tee" won't buffer serial input and
> cause a timeout, although on the test machine it doesn't.
>
> Ciao
>
> Dominik ^_^  ^_^
>
> --
>
> Dominik Vogt
>
-- 
*\Ben Klein*
Founder and Owner of Robosane, robobenklein@robosane.net
You can find me elsewhere online as 'robobenklein'.
If you need to contact me securely, I am also reachable via GPG, or on
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