Package: wlmodem
wl-95046 Python library for Water Linked underwater modemsPython library for communicating with Water Linked underwater modems.The library exposes the functionality of the modem: setting configuration, getting diagnostic, sending
and receiving packets.ResourcesWater Linked web siteModem documentationModem protocol specificationRepositoryRequirementsPython 2.7 or Python 3.6pipSupported modemsWater Linked Modem-M64Setup$ python3 -m pip install --user wlmodem
or
(venv)$ python3 -m pip install wlmodemQuick startConnecting to a modem and configuring the mode and channel:$python3>>>fromwlmodemimportWlModem>>>modem=WlModem("/dev/ttyUSB0")>>>modem.connect()True>>>modem.cmd_configure("a",4)True>>>modem.cmd_queue_packet(b"HelloSea")TrueUsageTheWlModemclass provides an easy interface to configure, send and receive data with a Water Linked modem.
A pair of modems must be configured on the same channel and with different roles to establish communication between them.AWlModemobject is initialized with the serial device name:fromwlmodemimportWlModemmodem=WlModem("/dev/ttyUSB0")Callconnect()to establish communication with the deviceifnotmodem.connect():print("Failed connecting to modem")sys.exit(1)Once connected we set the same channel and different roles on the pair of modems:# On modem 1:success=modem.cmd_configure("a",4)# On modem 2:success=modem.cmd_configure("b",4)If the tip of the modems are close to each other (<5cm) the modems will now link up.
The link status can be seen on the LEDs or by getting the diagnostic data.ifmodem.cmd_get_diagnostic().get("link_up"):print("Link is up")Once we have connected we can usecmd_queue_packetfunction to queue data for transmission.success=modem.cmd_queue_packet(b"HelloSea")In order to get data which one modem has received from the other modem use theget_data_packetfunction.
This function will by default waittimeoutseconds until a data packet is received before returning.
Iftimeoutis 0 it will immediately return with a packet (if available) orNoneif no packet has been received.pkt=modem.get_data_packet(timeout=0)ifpkt:print("Got data:",pkt)UDP-style transfersTheWlUDPSocketclass is a higher level abstraction which allows arbitrary sized UDP-like datagrams to be transferred.
This style of transfer is suitable for short messages and has low overhead at 3 bytes for each
datagram (1 start byte, 1 checksum and 1 end byte).
The datagram will be corrupted by any single modem packet dropped (while still taking the full time to transmit),
which means it is only suitable for short datagrams.
The Modem-M64 has a payload size of 8 bytes, so the chance of success given a chance of any packet lost and number of packets transferred is given by:chance_of_success=((100.0-chance_of_packet_loss)/100)**(number_of_packets_sent)*100For example, with a 5% chance of packet loss and datagram of 77 bytes (with the 3 overhead bytes this gives 10 packets):>>>((100.0-5)/100)**10*10059.87369392383787Ie. there is a 60% chance of successful transmission.Example of how to use theWLUDPSocketclass for transmission and reception of data:fromwlmodemimportWlModem,WlUDPSocketmodem=WlModem("/dev/ttyUSB0")modem.connect()wl_sock=WlUDPSocket(modem)wl_sock.send(b"There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss")received=wl_sock.receive()SimulatorAWlModemSimulatorclass can be used to simulate communication with a modem without a physical modem.
Once instantiated the object will behave similarly to a Water Linked Modem-M64.
Data packets that are queued using the simulator object is returned after a timeout.>>>fromwlmodemimportWlModemSimulator>>>modem=WlModemSimulator()>>>modem.connect()True>>>modem.cmd_queue_packet(b"HelloSim")True>>>modem.get_data_packet()b'HelloSim'ExamplesMultiple examples showing how to use the API is available in theexample/folder.DevelopmentThe code in this repository is unit tested withpytest.toxis used to automate testing on multiple Python versions.Run unit-tests with:pip install tox
toxFurther details on development of the repository is described inREADME_maintain.md