Bash, Serial I/O and Arduino

Question

So, I'm in a bit over my head, and I feel like I'm very close to a solution but it's just not working quite yet. Here's my situation:

I'm working with an Arduino MicroController, and I'm attempting to write two Bash scripts (right now running in MacOS 10.6) which will (a) print all serial data coming out of the Arduino unit to the standard output, and (b) allow me to send serial data to the Arduino unit. These scripts will then be called using Adobe AIR's NativeProcess API to allow a tight integration between the Arduino unit and a Flex AIR Application.

My two scripts are very simple -

Here's my WriteToSerial.sh script:

echo $1 > $2

($1 is obviously my string, $2 is the location of the serial port - currently /dev/tty.usbserial-A800eIUj)

And here's my ReadSerialOutput.sh script:

tail -f $1

($1 is the location of my serial port, currently /dev/tty.usbserial-A800eIUj)

The problem I'm having is that when I call either of these scripts (or even if I just type the commands directly into the Bash console), my computer just hangs - I can type characters, but nothing happens until I control-C out of the process.

HOWEVER, if I open the Arduino IDE and turn on the Serial Monitor, then tail -f the port, then close the serial monitor, then echo "test" > serial port, everything works just great.

This suggests to me that opening the Serial Monitor within the Arduino IDE is somehow initializing the serial port, which in turn allows me to tail it with no problem. This in turn suggests to me that I'm simply failing to input some sort of initialization command. However, I've been searching high and low for days and can't seem to find anything that addresses this issue.

And so this brings me to you, Stack Overflow. Please, if you have any idea what I'm talking about by all means weigh in - if only to tell me that I'm not crazy. And if you can help me figure this out, I'll happily tell everyone what a great person you are.

Cheers, and in the meantime I'm going back to Google. myk

Answer 1

Try adding an ampersand (&) to the end of the commands to put the process in the background. If the console is hanging up, then that means the script or process is still running on your current terminal, and you won't be able to input or click on anything until the process or script is done.

You can also try running the command in 1 terminal window, and open a new terminal window/tab, and try tailing from there.

Answer 2

Maybe try some serial command line tool similar to serial-1.0.

See: Serial port loopback/duplex test, in Bash or C? (process substitution)

Answer 3

On Linux, you need to call setserial to configure your serial port options (baud rate, parity, flow-control, etc) before you can read/write the port correctly.

You need to find a way to do this with your MacOS bash system.

Or you could write a python script to do this.

Answer 4

Try using the tool stty:

stty -F /dev/my_serial_port <baud_rate> cs8 cread clocal

As always, read the manpage before applying the above. cread allows you to receive data. You may want to omit clocal if you are using flow control if you are using flow control. If you aren't sure what the above settings are, ask, and I can write up a more complete answer.

Answer 5

Try / modify ttyecho:

http://www.humbug.in/2010/utility-to-send-commands-or-data-to-other-terminals-ttypts/

Answer 6

Check to see if sending data to / receiving data from the Arduino unit is working by using a different app such as Cornflake (serial terminal for Mac OS X) - instead of using the Arduino IDE & the Serial Monitor.

In addition, you may want to check out if you could benefit from switching to Xcode (in terms of debugging features, etc.).

See: Setting up Xcode to Compile & Upload to an Arduino ATMega328 (Duemilanove)

Answer 7

There's also Apple's SerialPortSample command line tool that allows you to set arbitrary baud rates:

// from: SerialPortSample/SerialPortSample.c
// ...
// Starting with Tiger, the IOSSIOSPEED ioctl can be used to set arbitrary baud rates
// other than those specified by POSIX. The driver for the underlying serial hardware
// ultimately determines which baud rates can be used. This ioctl sets both the input
// and output speed. 
// ...

For more information see: http://www.arduino.cc/playground/Interfacing/Cocoa

Another piece of Cocoa sample code that shows you how to talk to the Arduino microcontroller over a serial connection is objective-candarduino (hosted on Google code).