Adriano Carvalho1 1

1 Answer

I am developing an orientation controller. I have a development board which communicates with the sensor(a compass) through I2C. Because the board is pretty limited (no OS), I developed a simple program toreceive things like: (1) 'get 0' to read the sensor's register 0; (2) 'set 0 10' to set the sensor's register 0 withthe value 10. For each of these cases the board returns: (1) 'Done: 10.' (register 0 has the value 10); (2)'Done.'; and (3) 'error: ...' in case of error. With this, I am trying to develop a shell script (bash) to sendcommands and retrieve data in order to understand the sensor and develop the controller.

My problem is with the following code:

# read device output in the background.

head -n 1 /dev/ttyUSB0 &

head=$!

# (#1): without the following stmt I get:

# head: cannot open `/dev/ttyUSB0' for reading: : Protocol error

sleep 0.1

# send command to the device.

echo "get 0" > /dev/ttyUSB0

# (#2) wait for head.

while kill -0 $head 2>/dev/null ; do : ; done

I guess (#1) is caused by a read/write conflict between 'head' and 'echo', but I don't know why and I have noidea on how to solve it.

Another issue is in (#2) where I would like to use a timeout. I've tried something like:

timeout 1 bash -c "while kill -0 $head 2>/dev/null ; do : ; done"

But I get: Timeout: aborting command ``bash'' with signal 9 and the program gets stuck.

By the way, before the code above is executed I do initialize the serial port with:

stty -F /dev/ttyUSB0 9600 cs8 -cstopb

EDIT: I don't want an interactive terminal. I want to use this routine as necessary. This routine is thenecessary foundation of the controller (read/write sensor's registers) which later will be implemented in theboard.

bash port serial

edited Jun 26 at 13:01 asked Jun 26 at 9:57

Have you seen the following post? unix.stackexchange.com/questions/22545/… – jpe Jun 26 at 10:15

Why don't you just wait $head ? – Dennis Williamson Jun 26 at 11:25

@jpe: I don't want an interactive shell. I want to use this routine only when necessary. – Adriano Carvalho Jun26 at 12:52

feedback

To solve (#1) I modified the routine to use a fd:

# $1: the device filename, eg. /dev/ttyS0

# $2: number of lines to read before exit.

exec 3<>$1

Serial port control through a shell script

bash - Serial port control through a shell script - Stack Overflow http://stackoverflow.com/questions/11204860/serial-port-control-throu...

1 de 2 18/09/2012 9:01

Adriano Carvalho1 1

head -n "$2" 0<&3 &

wait_pid=$!

cat - 1>&3

wait $wait_pid

exec 3>&-

EDIT: To solve (#2), instead of providing the routine with timeout support I delegate that responsibility to thecaller. However, in case of timeout we need to clean up. For that I've added the following afterwait_pid=$! :

trap="if kill -0 $wait_pid ; then kill -TERM $wait_pid ; fi"

trap "$trap" SIGINT SIGKILL SIGTERM

edited Jun 27 at 8:20 answered Jun 27 at 7:34

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