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Serial port comms for Clojure

branch: master
README.md
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serial-port

A simple library for serial port communication with Clojure. Although serial communciation may be considered old tech, it's useful for a communicating with a plethora of devices including exciting new hardware such as the Monome and the Arduino.

Dependencies

serial-port has the following dependencies:

Installation

The easiest way to to install serial-port is requiring the serial-port clojar in your project.clj and using cake to pull the dependencies. Cake has great support for native dependencies and the serial-port clojar depends on the rxtx22 clojar which packages the RxTx native libraries.

All this means you simply need to add serial-port to your list of dependencies in your project.clj:

(defproject your-project "0.1.5"
  :description "Your fabulous project that uses a serial connection"
  :dependencies [[org.clojure/clojure "1.3.0"]
                 [serial-port "1.1.0"]])

(Where 1.1.0 is replaced with the version you wish to use.)

Then run cake deps and cake will pull the correct dependencies (both native libs and jars) and put them in the right place for you to use with cake repl or cake swank.

Usage

Using the library

Just make sure you pull in the serial-port namespace using something like:

(use 'serial-port)

Finding your port identifier

In order to connect to your serial device you need to know the path of the file it presents itself on. serial-port provides a simple function to list these paths out:

=> (list-ports)

0 : /dev/tty.usbmodemfa141
1 : /dev/cu.usbmodemfa141
2 : /dev/tty.Bluetooth-PDA-Sync
3 : /dev/cu.Bluetooth-PDA-Sync
4 : /dev/tty.Bluetooth-Modem
5 : /dev/cu.Bluetooth-Modem

In this case, we have an Arduino connected to /dev/tty.usbmodemfa141.

Problem on Ubuntu Linux

From ubuntu linux 11.04 and forward, you may not see your device. The RXTX library searches for serial ports with the /dev/ttySxx naming convention. Your device may be called /dev/ttyACM0 and so is not found.

From the repl point of view, you could make your system aware of it:

(System/setProperty "gnu.io.rxtx.SerialPorts" "/dev/ttyACM0")

From the OS point of view: You could create a symbolic link with a name that satisfies this, so for example:

sudo ln -s /dev/ttyACM0 /dev/ttyS42

src: http://rxtx.qbang.org/wiki/index.php/Discovering_comm_ports

Connecting with a port identifier

When you know the path to the serial port, connecting is just as simple as:

(open "/dev/tty.usbmodemfa141")

However, you'll want to bind the result so you can use it later:

(def port (open "/dev/tty.usbmodemfa141"))

Reading bytes

The simplest way to read bytes from the connection is to use on-byte. This allows you to register a hander fn which will be called for each byte received. So, to print out each byte just do the following:

(on-byte port #(println %))

It's also possible to register a handler for every n bytes. The monome communicates by sending pairs of bytes, one byte to describe whether a button was pressed or released, and another to describe the coordinates of the button. You can register a hander to receive pairs of bytes as follows:

(on-n-bytes port 2 (fn [[action coords]] ...))

If you wish to get raw access to the InputStream this is possible with the function listen. This allows you to specify a handler that will get called every time there is data available on the port and will pass your handler the InputStream to allow you to directly .read bytes from it. Both on-byte and on-n-bytes generate such handlers acting as a proxy between your specified handler and the incoming data events.

When the handler is first registered, the bytes that have been buffered on the serial port are dropped by default. This can be changed by passing false to on-byte, on-n-bytes or listen as an optional last argument.

Only one listener may be registered at a time. If you want to fork the incoming datastream to a series of streams, you might want to consider using lamina. You can then register a handler which simply enqueues the incoming serial data to a lamina channel which you may then fork and map according to your whim.

Finally, you may remove your listener with remove-listener.

Writing bytes

The simplest way to write bytes is by passing a byte array to write:

(write port my-byte-array)

There are a couple of convenience functions available if you're dealing with plain Integers. write-int allows you to write a simple integer to the serial port and write-int-seq allows you to pass a sequence of integers which are then converted to a byte array which is subsequently written to the serial port:

(write-int port 20)
(write-int-seq port [20 10 2 100])

Closing the port

Simply use the close function:

(close port)

Contributors

  • Sam Aaron
  • Jeff Rose

License

Copyright (C) 2011 Sam Aaron

Distributed under the Eclipse Public License, the same as Clojure.

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