Interfacing with Python

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Revision as of 16:19, 25 July 2016 by Paisamar (Talk | contribs) (Step 2)

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Introduction

In this tutorial you will learn how to programmatically communicate with the Tmote Sky using the Python programming language. This will enable you to do such things as process data from your mote in real-time. In addition, you can send commands or data back to the mote to impact its operation. The possibilities are endless.

Setup

This tutorial was written and tested using the following:

  • Contiki 2.7
  • Python 2.7.3 (and pySerial)
  • Ubuntu 12.04
  • Tmote Sky

Connect the Tmote Sky to your computer using a USB cable and install the Sky Shell example. See the @Sky Shell@ tutorial for instructions on how to do this. We use this example so that we’ll have data to ensure that we are correctly reading and writing to the mote.

Step 1

Create a Python file called serial.py containing the following code:

#!/usr/bin/python
import serial
ser = serial.Serial(
   port='/dev/ttyUSB0',\
   baudrate=115200,\
   parity=serial.PARITY_NONE,\
   stopbits=serial.STOPBITS_ONE,\
   bytesize=serial.EIGHTBITS,\
   timeout=0)
print("connected to: " + ser.portstr)
ser.write("help\n");
while True:
	line = ser.readline();
	if line:
		print(line),
ser.close()

Note: This code assumes the mote you are using for this tutorial is connected to /dev/ttyUSB0. Please check this using the make motelist command as shown in the figure below. If the mote you are using is connected to a different device file, please modify the Python code accordingly.


Sample output of make motelist

Step 2

Run the Python code using the command:

python serial.py

If you encounter any errors, see the following link for troubleshooting - http://anrg.usc.edu/contiki/index.php/Troubleshooting

You should see output similar to the following:

connected to: /dev/ttyUSB0
Available commands:
?: shows this help
binprint: print binary data in decimal format
blink [num]: blink LEDs ([num] times)
collect: collect data from the network
collect-view-data: sensor data, power consumption, network stats
echo <text>: print <text>
energy: print energy profile
exit: exit shell
hd: print binary data in hexadecimal format
help: shows this help
kill <command>: stop a specific command
killall: stop all running commands
mac <onoroff>: turn MAC protocol on (1) or off (0)
netcmd <command>: run a command on all nodes in the network
nodeid: set node ID
null: discard input
packetize: put data into one packet
power: print power profile
powerconv: convert power profile to human readable output
powertrace [interval]: turn powertracing on or off, with reporting interval <interval>
quit: exit shell
randwait <maxtime> <command>: wait for a random time before running a command
reboot: reboot the system
repeat <num> 

Understanding the Code

 import serial

The first line will include the module for the serial port API. This API is provided by pySerial.

ser = serial.Serial(
    port='/dev/ttyUSB0',\
    baudrate=115200,\
    parity=serial.PARITY_NONE,\
    stopbits=serial.STOPBITS_ONE,\
    bytesize=serial.EIGHTBITS,\
    timeout=0)

This next line instantiates an object with the appropriate serial port configuration for communication with the Sky mote. The necessary settings are shown in the table below.

Serial Configuration
Baud rate 115200
Data bits 8
Parity None
Stop bits 1
 print("connected to: " + ser.portstr)

The print statement is simply a sanity check. It just reminds us which port we are connected to.

 ser.write("help\n");

This line demonstrates how data can be written to the serial port. In this example we send the command "help" to the Sky Shell so that it will send back the list of shell commands it supports.

while True:
     line = ser.readline();
     if line:
	print(line)

Here, we read data from the serial port indefinitely and print it out, one line at a time. Note that in this case, line will typically end with a newline.

To terminate the program, you can use Ctrl + C to send an interrupt signal.

 ser.close()

This last line never actually gets executed but it shows how the serial resource can be freed.


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