# Monitor a Channel Using a Database

    """dbmonitor.py -- Read CAN messages using a database

    This script will use canlib.canlib and canlib.kvadblib to monitor a CAN
    channel, and look up all messages received in a database before printing them.

    It requires a CANlib channel with a connected device capable of receiving CAN
    messages, some source of CAN messages, and the same database that the source is
    using to generate the messages.

    In this example the channel is opened with flag canOPEN_ACCEPT_LARGE_DLC (optional).
    This enables a DLC larger than 8 bytes (up to 15 for classic CAN). If
    canOPEN_ACCEPT_LARGE_DLC is excluded, generated frames with DLC > 8, will attain
    a DLC of 8 on the receiving end, which may compromise the DLC equivalence
    check.

    The source of the messages may be e.g. the pinger.py example script.

    """
    import argparse

    from canlib import canlib, kvadblib

    bitrates = {
        '1M': canlib.canBITRATE_1M,
        '500K': canlib.canBITRATE_500K,
        '250K': canlib.canBITRATE_250K,
        '125K': canlib.canBITRATE_125K,
        '100K': canlib.canBITRATE_100K,
        '62K': canlib.canBITRATE_62K,
        '50K': canlib.canBITRATE_50K,
        '83K': canlib.canBITRATE_83K,
        '10K': canlib.canBITRATE_10K,
    }

    def printframe(db, frame):
        try:
            bmsg = db.interpret(frame)
        except kvadblib.KvdNoMessage:
            print("<<< No message found for frame with id %s >>>" % frame.id)
            return

        if (not bmsg._message.dlc == bmsg._frame.dlc):
            print("<<< Could not interpret message because DLC does not match for frame with id %s >>>" % frame.id)
            print("\t- DLC (database): %s" % bmsg._message.dlc)
            print("\t- DLC (received frame): %s" % bmsg._frame.dlc)
            return

        msg = bmsg._message

        print('┏', msg.name)

        if msg.comment:
            print('┃', '"%s"' % msg.comment)

        for bsig in bmsg:
            print('┃', bsig.name + ':', bsig.value, bsig.unit)

        print('┗')

    def monitor_channel(channel_number, db_name, bitrate, ticktime):
        db = kvadblib.Dbc(filename=db_name)

        ch = canlib.openChannel(channel_number, canlib.canOPEN_ACCEPT_VIRTUAL | canlib.canOPEN_ACCEPT_LARGE_DLC)
        ch.setBusOutputControl(canlib.canDRIVER_NORMAL)
        ch.setBusParams(bitrate)
        ch.busOn()

        timeout = 0.5
        tick_countup = 0
        if ticktime <= 0:
            ticktime = None
        elif ticktime < timeout:
            timeout = ticktime

        print("Listening...")
        while True:
            try:
                frame = ch.read(timeout=int(timeout * 1000))
                printframe(db, frame)
            except canlib.CanNoMsg:
                if ticktime is not None:
                    tick_countup += timeout
                    while tick_countup > ticktime:
                        print("tick")
                        tick_countup -= ticktime
            except KeyboardInterrupt:
                print("Stop.")
                break

    if __name__ == '__main__':
        parser = argparse.ArgumentParser(
            description="Listen on a CAN channel and print all signals received, as specified by a database.")
        parser.add_argument('channel', type=int, default=1, nargs='?', help=(
            "The channel to listen on."))
        parser.add_argument('--db', default="engine_example.dbc", help=(
            "The database file to look up messages and signals in."))
        parser.add_argument('--bitrate', '-b', default='500k', help=(
            "Bitrate, one of " + ', '.join(bitrates.keys())))
        parser.add_argument('--ticktime', '-t', type=float, default=0, help=(
            "If greater than zero, display 'tick' every this many seconds"))
        args = parser.parse_args()

        monitor_channel(args.channel, args.db, bitrates[args.bitrate.upper()], args.ticktime)

## Description

Any CAN messages received on the specified channel will be looked up in the database using `canlib.kvadblib.Dbc.interpret`, which allows the script to print the “phys” value of each signal instead of just printing the raw data (as Monitor a Channel does). The script also prints the message’s name and comment (if available), as well as the signals name and unit.

## Sample Output

    ┏ EngineData
    ┃ PetrolLevel: 0.0 l
    ┃ EngPower: 12.0 kW
    ┃ EngForce: 0.0 N
    ┃ IdleRunning: 0.0
    ┃ EngTemp: -30.0 °C
    ┃ EngSpeed: 7735.0 rpm
    ┗
    ┏ GearBoxInfo
    ┃ EcoMode: 0.0
    ┃ ShiftRequest: 0.0
    ┃ Gear: 0.0
    ┗
    ┏ EngineData
    ┃ PetrolLevel: 0.0 l
    ┃ EngPower: 28.0 kW
    ┃ EngForce: 0.0 N
    ┃ IdleRunning: 0.0
    ┃ EngTemp: -30.0 °C
    ┃ EngSpeed: 3467.0 rpm
    ┗
    ┏ GearBoxInfo
    ┃ EcoMode: 1.0
    ┃ ShiftRequest: 0.0
    ┃ Gear: 0.0
    ┗
    ┏ EngineData
    ┃ PetrolLevel: 0.0 l
    ┃ EngPower: 0.0 kW
    ┃ EngForce: 0.0 N
    ┃ IdleRunning: 0.0
    ┃ EngTemp: -50.0 °C
    ┃ EngSpeed: 1639.0 rpm
    ┗
    ┏ GearBoxInfo
    ┃ EcoMode: 1.0
    ┃ ShiftRequest: 0.0
    ┃ Gear: 1.0
    ┗
    ┏ EngineData
    ┃ PetrolLevel: 60.0 l
    ┃ EngPower: 0.0 kW
    ┃ EngForce: 0.0 N
    ┃ IdleRunning: 0.0
    ┃ EngTemp: 142.0 °C
    ┃ EngSpeed: 0.0 rpm
    ┗
    ┏ GearBoxInfo
    ┃ EcoMode: 0.0
    ┃ ShiftRequest: 0.0
    ┃ Gear: 0.0
    ┗
    ┏ EngineData
    ┃ PetrolLevel: 172.0 l
    ┃ EngPower: 51.0 kW
    ┃ EngForce: 0.0 N
    ┃ IdleRunning: 0.0
    ┃ EngTemp: -50.0 °C
    ┃ EngSpeed: 0.0 rpm
    ┗
    ┏ GearBoxInfo
    ┃ EcoMode: 0.0
    ┃ ShiftRequest: 0.0
    ┃ Gear: 0.0
    ┗