def on_receive(p, ch_rx=None, ch_tx=None):
    """
    Callback: get's invoked whenever a packet has been received.
    :param p: Payload of the received packet.
    """

    d = {}

    t_now_ns = time.monotonic_ns()
    ts = datetime.utcnow()
    ts_unixtime = ts.timestamp()
    #d['ts_unixtime'] = ts_unixtime
    d['isodate'] = ts.isoformat()
    #d['rawdata'] = " ".join([f"{b:02x}" for b in p])
    # print(ts.isoformat(), end='Z ')

    # check crc8
    crc8 = f_crc8(p[:-1])
    #d['crc8_valid'] = True if crc8==p[-1] else False

    # interpret content
    mid = p[0]
    #d['mid'] = mid
    #d['response_time_ns'] = t_now_ns-t_last_tx
    #d['ch_rx'] = ch_rx
    #d['ch_tx'] = ch_tx
    #d['src'] = 'src_unkn'
    #d['name'] = 'name_unkn'
 
    if mid == 0x95:
        src, dst, cmd = struct.unpack('>LLB', p[1:10])
        #d['src'] = f'{src:08x}'
        #d['dst'] = f'{dst:08x}'
        d['cmd'] = cmd
        # print(f'MSG src={d["src"]}, dst={d["dst"]}, cmd={d["cmd"]}:')

        if cmd==1:
            # d['name'] = 'dcdata1'
            uk1, u1, i1, i2, p1, p2, uk2, t1Wh = struct.unpack(
                '>HHHHHHHH', p[10:26])
            d['uk_1_1'] = uk1
            d['uk_1_2'] = uk2
            d['u12_V'] = u1/10
            d['i1_A'] = i1/100
            d['i2_A'] = i2/100
            d['p1_W'] = p1/10
            d['p2_W'] = p2/10
            d['Tot1_kWh'] = t1Wh/1000
            d['(pA12_W)'] = round(d['u12_V']*(d['i1_A']+d["i2_A"]), 1)

        elif cmd==2:
            # d['name'] = 'dcdata2'
            uk3, t2Wh, d1Wh, d2Wh, u2, i3, i4, p3 = struct.unpack(
                '>HHHHHHHH', p[10:26])
            d['uk_2_1'] = uk3
            d['u34_V'] = u2/10
            d['i3_A'] = i3/100
            d['i4_A'] = i4/100
            d['p3_W'] = p3/10
            d['Day1_Wh'] = d1Wh
            d['Day2_Wh'] = d2Wh
            d['Tot2_kWh'] = t2Wh/1000
            d['(pA34_W)'] = round(d['u34_V']*(d['i3_A']+d['i4_A']), 1)

        elif cmd==3:
            # d['name'] = 'ACdata1'
            p4, uk4, t4Wh, uk5, t3Wh, d4Wh, d3Wh, U_ac = struct.unpack(
                '>HHHHHHHH', p[10:26])
            d['uk_3_1'] = uk4
            d['p4_W'] = p4/10
            d['Day3_Wh'] = d3Wh
            d['Day4_Wh'] = d4Wh
            d['Tot3_kWh'] = t3Wh/1000
            d['Tot4_kWh'] = t4Wh/1000
            d['U_ac_V'] = U_ac/10

        elif cmd==132:  # 0x84
            # d['name'] = 'ACdata2'
            f, P, uk5, iac, uk6, t_wr, uk7, uk8 = struct.unpack(
                '>HHHHHHHH', p[10:26])
            d['uk_132_1'] = uk5
            d['uk_132_2'] = uk6
            d['uk_132_3'] = uk7
            d['uk_132_4'] = uk8
            d['f'] = f/100
            d['Iac_A'] = iac/100
            d['twr_C'] = t_wr/10
            d['Pac_W'] = P/10

        else:
            print(f'unknown cmd {cmd}')
    else:
        print(f'unknown frame id {p[0]}')

    # output to stdout
    if d:
        print(json.dumps(d, indent=4, separators=(", ", ": ")))
        
    # output to MQTT
    '''
    if d:
        j = json.dumps(d)
        mqtt_client.publish(f"ahoy/{d['src']}/{d['name']}", j)
        if d['cmd']==2:
            mqtt_client.publish(f'ahoy/{d["src"]}/emeter/0/voltage', d['u_V'])
            mqtt_client.publish(f'ahoy/{d["src"]}/emeter/0/power', d['p_W'])
            mqtt_client.publish(f'ahoy/{d["src"]}/emeter/0/total', d['wtot1_Wh'])
            mqtt_client.publish(f'ahoy/{d["src"]}/frequency', d['f_Hz'])
        if d['cmd']==1:
            mqtt_client.publish(f'ahoy/{d["src"]}/emeter-dc/0/power', d['p1_W'])
            mqtt_client.publish(f'ahoy/{d["src"]}/emeter-dc/0/voltage', d['u1_V'])
            mqtt_client.publish(f'ahoy/{d["src"]}/emeter-dc/0/current', d['i1_A'])
            mqtt_client.publish(f'ahoy/{d["src"]}/emeter-dc/1/power', d['p2_W'])
            # mqtt_client.publish(f'ahoy/{d["src"]}/emeter-dc/1/voltage', d['u2_V'])
            mqtt_client.publish(f'ahoy/{d["src"]}/emeter-dc/1/current', d['i2_A'])
        if d['cmd']==131:
            mqtt_client.publish(f'ahoy/{d["src"]}/temperature', d['t_C'])
    '''