From: Dominik Vogt <dominik.vogt@gmx.de>
To: Zsh Users <zsh-users@zsh.org>
Subject: Shell io from and to serial device
Date: Thu, 14 Feb 2019 01:00:42 +0100 [thread overview]
Message-ID: <20190214000042.ed73yom5s26pst5p@gmx.de> (raw)
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
next reply other threads:[~2019-02-14 13:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-14 0:00 Dominik Vogt [this message]
2019-02-14 0:56 ` Ben Klein
2019-02-15 1:02 ` Bart Schaefer
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