rest tutorial

Contiki REST/CoAP Quickstart using Econotags

Contiki has an implementation of the IETF CORE (Constrained RESTful Environments) working group's CoAP layer (Constrained Application Protocol). CoAP is a RESTful application layer that uses HTTP-like methods (GET, POST, PUT, DELETE) to interact with constrained networks. CoAP operates over UDP and supports reliable transmission.

This tutorial will show you how to run Contiki's CoAP demo on Redwire Econotags using an RPL border-router.

1. Run a RPL border-router and tunnel

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See the RPL HOWTO for details about running a RPL border-router.

2. Build and run the rest-server-example on a second Econotag

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The following must be done on the contiki-mc1322x.git tree

git clone git://git.devl.org/git/malvira/contiki-mc1322x.git

Contiki CVS is currently down and the new SCM system hasn't been set up yet. The necessary changes will be pushed as soon as the new SCM is available. - 6 Februrary 2011

To build the rest-server-example:

cd contiki-mc1322x/examples/rest-example
make TARGET=redbee-econotag

This will produce the binary image rest-server-example_redbee-econotag.bin, which you can load directly on to an mc1322x and execute.

mc1322x-load.pl -f rest-server-example_redbee-econotag.bin -t /dev/ttyUSB3

Then press the reset button to connect to the bootloader.

In this example, we are loading the CoAP server on to the econotag on /dev/ttyUSB3

You should see boot up messages similar to this:

CONNECT
Size: 62096 bytes
Sending rest-server-example_redbee-econotag.bin
done sending files.
performing ring osc cal
crm_status: 0xc0000
sys_cntl: 0x18
ring osc cal complete
cal_count: 0x17e17e0
cal factor: 100
hib_wake_secs: 2000
loading rime address from flash.
Rime started with address 00:50:C2:AB:C0:00:00:23
nullmac nullrdc, channel check rate 100 Hz, radio channel 26
Tentative link-local IPv6 address
fe80:0000:0000:0000:0250:c2ab:c000:0023
Tentative global IPv6 address aaaa:0000:0000:0000:0250:c2ab:c000:0023
Starting 'Rest Server Example'
COAP Server

The last line indicates that the server will be using COAP. As an alternative, you can build the server to use HTTP instead with:

make TARGET=redbee-econotag WITH_COAP=0 

3. Download and install the Copper Firefox Plugin

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The Copper Plugin for Firefox provides the coap: URL access method as well as an interface to easily send coap requests.

Download and install the plugin from here:

• Copper plugin homepage
• Install link:copper-0.3.0pre2.xpi

4. Open Copper

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Open a new Firefox tab and click on the orange CU button in the lower right.

The initial CU screen will look like this:

Type in the the URL of the coap node with the default port number of "61616":

• Don't forget the brackets ( [ ] ) in the URL

• Make sure to use the IPv6 address of your coap server. You can get this from the boot up messages or from the webpage served by your border-router.

• You must always press Enter after changing the URL.

5. GET .well-known/core resources

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Now click on the red "./well-known/core" button: this changes the URL to the .well-known/core resource.

Then click GET to perform a get. You should see an acknowledgement that the GET was successful (returns 200 OK). The payload should return:

</helloworld>;n="HelloWorld",</led>;n="LedControl",</light>;n="Light

Which is are the well-known resources that this node advertises; see the COAP specification for details.

6. PUT,POST the led resource state

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You can PUT or POST to change the state of the LED.

Type in the following URL and press enter:

coap://[aaaa::250:c2ff:fea8:c48e]:61616/led?color=green

Be sure to use the proper IP address. For this URL: we will perform actions on the led resource with a query string of color=green.

In the payload, type:

mode=on

That is the payload that will be PUT or POSTed. The COAP server detects the mode string and activates the LED accordingly (with the color chosen by the query string).

Then click PUT or POST to perform the request.

You should get a successful return code (200 OK) and the green LED should turn on. If you PUT/POST mode=off the led will turn off.

The econotag only has two LEDs: a green and a red. The red LED is used to indicate radio transmission by default and so cannot be used in this demo. The Coniki blue LED is connected to GPIO 43. You can toggle it, but you won't see anything unless you hook something up to this pin.

7. Other resources

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The rest-server-example also provides helloworld and light as GETtable resources.

coap://[aaaa::250:c2ff:fea8:c48e]:61616/helloworld
coap://[aaaa::250:c2ff:fea8:c48e]:61616/light

The econotag does not have a light sensor. The light resource will always return 0. At a latter date, this sensor will be connected to one of the ADC pins.