BERadioMessageDecoder

Introduction

The BERadio C++ encoder library provides automatic message fragmentation yielding self-contained messages fitting into a defined maximum payload size. Its default setting is MTU_SIZE_MAX 61, making it suitable for typical ISM applications.

The BERadioMessageDecoder is a decoder machinery for reassembling fragmented BERadio messages into whole packets.

It works by waiting for a defined amount of time for new messages arriving. Its default setting is REASSEMBLY_TIMEOUT = 2.5, making it suitable to reassemble messages spread across this time window into compound data packages. After the defined time, BERadioMessageDecoder will release these data packages for consumption by downstream software components.

Demonstration

Let’s show the functionality of the proof-of-concept.

BERadio messages

Let’s pretend there are four messages in flight:

  • Three message fragments will arrive from node 2 containing values from a temperature array (temp1-5), two weight values (wght1-2), a single one for each humidity (hum1) and rssi (rssi1) and one cpu cycle counter (loop1).
  • There’s another message from node 3 containing values for temp1, hum1 and wght1.

Let’s define these messages:

>>> messages = [
...     'd1:#i2e1:_2:h11:tli2168ei1393ei3356ei1468ei1700ee1:hlee',
...     'd1:#i2e1:_2:h12:h0li8370ee1:wli53503600ei2590ee1:lli15100eee',
...     'd1:#i3e1:_2:h11:tli2168ee2:h0li930ee1:wli4242eee',
...     'd1:#i2e1:_2:h11:rli-6600eee',
... ]

Decoding the first message is easy and will get you an understanding about what’s actually inside:

>>> from beradio.message import BERadioMessage
>>> print BERadioMessage.json(str(messages[0]))         
{
    "data": {
        "temp1": 21.68,
        "temp2": 13.93,
        "temp3": 33.56,
        "temp4": 14.68,
        "temp5": 17.0
    },
    "meta": {
        "gateway": "None",
        "network": "None",
        "node": "2",
        "profile": "h1",
        "protocol": "beradio2",
        "time": ...
    }
}

Setup machinery

Import the decoder module

>>> from beradio.message import BERadioMessageDecoder

and make an instance of it

>>> decoder = BERadioMessageDecoder()

Getting started

Let’s stuff the first two messages into the decoder, simulating a transmission delay after each one:

>>> decoder.read(messages[0])
>>> time.sleep(0.5)
>>> decoder.read(messages[1])
>>> time.sleep(0.5)

Let’s just stuff the remaining two messages into the decoder quickly to reduce runtime:

>>> decoder.read(messages[2])
>>> decoder.read(messages[3])

Reassembly

After reassembling, all the data received during the default time window of 2.5 seconds will be available as a whole bunch, keyed by node id. Enjoy:

>>> print decoder.to_json()
{
    "2": {
        "data": {
            "hum1": 83.7,
            "loops1": 151.0,
            "rssi1": -66.0,
            "temp1": 21.68,
            "temp2": 13.93,
            "temp3": 33.56,
            "temp4": 14.68,
            "temp5": 17.0,
            "wght1": 535036.0,
            "wght2": 25.9
        },
        "messages": [
            "d1:#i2e1:_2:h11:tli2168ei1393ei3356ei1468ei1700ee1:hlee",
            "d1:#i2e1:_2:h12:h0li8370ee1:wli53503600ei2590ee1:lli15100eee",
            "d1:#i2e1:_2:h11:rli-6600eee"
        ],
        "meta": {
            "gateway": "None",
            "network": "None",
            "node": "2",
            "profile": "h1",
            "protocol": "beradio2",
            "time": ...
        }
    },
    "3": {
        "data": {
            "hum1": 9.3,
            "temp1": 21.68,
            "wght1": 42.42
        },
        "messages": [
            "d1:#i3e1:_2:h11:tli2168ee2:h0li930ee1:wli4242eee"
        ],
        "meta": {
            "gateway": "None",
            "network": "None",
            "node": "3",
            "profile": "h1",
            "protocol": "beradio2",
            "time": ...
        }
    }
}