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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 Mac OS X 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 Adobe 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)

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 Ctrl + C out of the process.

However, if I open the Arduino IDE and turn on the Serial Monitor, then tail -f the port, close the serial monitor, and 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.

What is the solution?

Peter Mortensen
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Myk
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  • I should add - I've tried using "stty -F /dev/tty.usbserial-XXXXX" but I get "stty: illegal option -- -F" - which doesn't sound right to me. – Myk Oct 12 '10 at 19:17
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    OK, so now I've learned that -F and --file for some reason don't work in my OS but that "-f" works - so I do that, and still no dice. – Myk Oct 12 '10 at 19:53
  • You might want to ask this question on http://electronics.stackexchange.com/, they deal with questions related to Arduinos and embedded programming. – J. Polfer Oct 13 '10 at 14:22
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    Since **tail** is always running till last line, which will not appear until serial bus is closed, found **head** rather useful `head --lines 1 < /dev/ttyUSB0` – McPeppr Jun 21 '16 at 09:51

10 Answers10

34

I get the same problem too. I use Arduino Uno with Ubuntu 12.04. After a few hours of searching and trying, I find out that Arduino will reset when the serial device is opened for the first time，but will not reset when the serial device is opened again.

So, run command - echo "input string" > /dev/ttyXXX in bash will reset Arduino and send "input string" immediately. Arduino need take some time to initialize, and is not quick enough to receive this string. cat /dev/ttyXXX will reset Arduino too.

When /dev/ttyXXX is opened in somewhere firstly, these commands will work.

Here is my solution:

1) open /dev/ttyXXX by redirecting /dev/ttyXXX to file description 3

exec 3<> /dev/ttyXXX

2) wait for Arduino's initialization

sleep 1

3) communicate with Arduino

echo "input something" >&3

cat <&3

4) close /dev/ttyXXX

exec 3>&-

Yihui Xiong
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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 aren't sure what the above settings are, ask, and I can write up a more complete answer.

Shawn J. Goff
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J. Polfer
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    Yeah, I've been messing around with the stty thing. In MacOS it seems like I can't use -F, I have to use -f (same command, just different syntax). Other than that sure, I will input a command like that and get no errors - but then it still hangs when I try to echo "TEST" > /dev/tty.usbserial-XXX – Myk Oct 13 '10 at 17:37
  • I'm almost starting to wonder if it's this computer - I have only tested it here, I will have to try a dif system when I get home tonight. – Myk Oct 13 '10 at 17:38
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    @Myk - I kinda doubt a different computer will change this. Something that might block a send might be a flow-control issue - if the CTS line isn't high, no data will be sent. You can get around this in hardware by looping the RTS pin back to the CTS pin. Or by setting clocal. – J. Polfer Oct 13 '10 at 17:43
  • If it's not too much trouble, what's flow-control and CTS? I tried setting clocal as per your advice above, but no dice. Sadly I'm sort of a *nix noob - learning fast, but there's much I don't know. – Myk Oct 13 '10 at 17:46
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    CTS is one of the serial port's signals, usually used together with RTS for hardware flow control. Flow control is using some sort of protocol to tell the other end to stop transmitting until we have processed the data we have already received. – ninjalj Oct 13 '10 at 18:06
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    @Myk: can you run `stty -a < /dev/tty.usbserial-A800eIUj` while you have the serial port working on the Arduino IDE? That would give you the settings to use. – ninjalj Oct 13 '10 at 18:13
  • You might want to see this: http://electronics.stackexchange.com/questions/5167/set-rs232-port-options-from-macos-x-cli/5175#5175 – J. Polfer Oct 13 '10 at 21:53
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    I switched my approach to solving this problem - I'm rolling with Python, which reads my serial port in two lines of code. Still, though, this answer was the most helpful and links in the comment to the other question so I'm going to go ahead and accept this. Thanks for your help! – Myk Oct 28 '10 at 15:26
4

I struggled with this problem also, trying no end of stty settings and tricks to cat my files to /dev/tty.usbserial-FTF7YNJ5 (in my case) whilst standing on one toe, etc.

Then I did an ls /dev and noticed /dev/cu.usbserial-FTF7YNJ5 -- oh, what's this? Apparently, a 'calling unit' version of the device that doesn't expect or provide any flow control. Dumps bytes to the port. Exactly what I needed.

So just do: cat super_file.bin > /dev/cu.usbserial-XXXXX

Hope this helps. And only now that I know the answer, I found this: http://stuffthingsandjunk.blogspot.com/2009/03/devcu-vs-devtty-osx-serial-ports.html

chrism
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  • Interesting, I will give that a try next time I have a minute to dive into Arduino work! Thanks for the suggestion! – Myk Apr 24 '11 at 15:10
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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 Mac OS X Bash system.

Or you could write a Python script to do this.

Community
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J. Polfer
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  • Yeah, I've got a python script working, actually. But I'd like to not have the python runtime as a dependency on host machines if I can avoid it. > – Myk Oct 13 '10 at 14:57
  • ...if it were just the native Python install I'd be ok with it, but it also need PySerial installed in order to run so that makes it a bit more complex. If I can't figure this out then that's what I'll do, but I feel like there HAS to be a way to make this work! – Myk Oct 13 '10 at 16:05
  • @Myk - Since you want to avoid python, You might be able to get the same effect you observed (I can use my own tools when the Arduino IDE is open) by writing a small C program that uses tcsetattr() that sets the port options first. The easiest way is to figure out the CLI command to set serial port options on your Mac. – J. Polfer Oct 13 '10 at 17:14
  • @Myk - Please see my new answer. stty is the traditional command in *nixes for adjusting serial port options. – J. Polfer Oct 13 '10 at 17:30
  • Yeah, I am almost thinking a C program is the way to go - I'm tempted to just reverse-engineer serproxy to make it output to standard output rather than a socket, and then bam. – Myk Oct 13 '10 at 18:22
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Maybe try some serial command line tool similar to serial-1.0.

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

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dan
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0

A one-liner Something that works really well for datalogging, and acting on data:

Summary
  • monitoring: the arduino output can trigger actions on the computer
  • data-logging: it simultaneously save that streaming data to a file
  • notchecked? sending-messages: I haven't tried sending data yet to the arduino, but see the second example, might be able to send a message to the serial port via some cmdline util.

the following timestamps and sends to stdout

cat /dev/cu.usbmodem1421 | awk '{ for (i=0; i<NF; i++) printf $i + system("echo  , `date`")}'

Sample Output:

enter image description here

This method can even be adapted to monitor and act upon the data in real time:

cat /dev/cu.usbmodem1421 | awk '{ for (i=0; i<NF; i++) printf $i + system("echo , `date`)}'

more examples here: https://github.com/gskielian/Arduino-DataLogging/tree/master/Bash-One-Liner

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gskielian
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0

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.

bm7150
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  • Yeah, I've got multiple terminal windows so I don't think that's the problem - I mean, even echo "Test" > SERIAL is freezing up, and that should be a single process that runs and stops. It's the fact that they're hanging that's confusing me. – Myk Oct 12 '10 at 19:23
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Try / modify ttyecho:

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

tilo
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  • I don't think that's it, since echo works just fine once I've initialized the serial port using the Arduino IDE. Both my echo and my tail -f do EXACTLY what I want them too once I actually have access to the port. – Myk Oct 13 '10 at 17:35
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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)

tol
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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).

ceeit
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