Purpose of "mux criteria" of the C++ example?

[mf01]

What is the purpose of the "mux criteria"? The C++ example denotes the following criteria:

const dbcppp::ISignal* mux_sig = msg->MuxSignal();
if (sig.MultiplexerIndicator() != dbcppp::ISignal::EMultiplexer::MuxValue ||
    (mux_sig && mux_sig->Decode(frame.data) == sig.MultiplexerSwitchValue()))

After investigating the code, I did not understand the purpose of this criteria. Furthermore, when I call sig.Decode(frame.data) to a (correct sized) buffer. I got the expected data (in my examinated cases).

The C example has no obvious code therefore.

[xR3b0rn]

In addition to normal signals, DBC also offers an opportunity to specify a multiplexer signal and multiplexed signals in messages. If a multiplexer signal is specified in a message, the multiplexer signal determines which multiplexed signals are in the frame.

E.g. from tests/test_files/dbc/multiplex.dbc:

BO_ 2148676694 Message1: 8 Vector__XXX
 SG_ BIT_K m24 : 28|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_D m24 : 32|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_B m24 : 33|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_F m24 : 39|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_H m24 : 38|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_E m24 : 29|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_A m24 : 26|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_L m8 : 24|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_G m8 : 23|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_C m8 : 19|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ BIT_J m8 : 18|1@1+ (1,0) [0|0] "" Vector__XXX
 SG_ Multiplexor M : 2|6@1+ (1,0) [0|0] "" Vector__XXX

The message Message1 specifies the signal Multiplexor (M) as the multiplexer signal, the other signals are multiplexed (m<number>) . If the multiplexer signal value equals 24, the frame contains the signals specified with m24, analogue for m8.

So to have a generic algorithm which decodes signals from an arbritary DBC, you first have to check, if the signal is a multiplexed signal. And if so, you have to compare the value from the DBC against the multiplexer value from the data frame you've received.

[mf01]

OK, now I understand this. Thank you-

[MichaelBMiner]

This is great info, but how does one get the mux value using C? I have attempted to do this but do not properly parse the mux value.

BO_ 2566544894 PGN_64093_EVSE_1_Power_Max_Schedule: 8 EVCC
 SG_ MUX M : 0|4@1+ (1,0) [0|0] "" EV
 SG_ EVSE1_Schedule_Index m0 : 4|8@1+ (1,0) [0|250] "count" EV
 SG_ EVSE1_Max_Schedule_Index m0 : 12|8@1+ (1,0) [0|250] "count" EV
 SG_ EVSE1_Schedule_Id m0 : 20|16@1+ (1,0) [0|65535] "count" EV
 SG_ EVSE1_PMax_Schedule_Id m0 : 36|16@1+ (1,0) [0|65535] "count" EV
 SG_ EVSE1_Entry_Power_Max m1 : 4|32@1- (1,-2000000000) [-2000000000|2211081215] "W" EV
 SG_ EVSE1_Entry_Start_Time m2 : 4|32@1+ (1,0) [0|4211081215] "s" EV
 SG_ EVSE1_Entry_Duration m3 : 4|32@1+ (1,0) [0|4211081215] "s" EV

[xR3b0rn]

You can use this function: dbcppp_SignalMultiplexerSwitchValue

[MichaelBMiner]

const dbcppp_Signal* signal = dbcppp_MessageSignals_Get(msg, j);
dbcppp_ESignalMultiplexer signal_mux_type = dbcppp_SignalMultiplexerIndicator(signal);
uint64_t signal_mux_value = dbcppp_SignalMultiplexerSwitchValue(signal);

No matter the can data, this always returns 0.