Decoding returns wrong value.

[tylerbucher]

Describe the bug
When decoding a dbc signal like SG_ Service M : 11|4@0+ (1,0) [0|15] "" Vector__XXX and data like this payload: [3, 65, 13, 55, 255, 255, 255, 255] the expected output should be 1 not 8.

Additional context
@bit-dream BitUtils#extractBitRange when in big endian mode this function seems to move the start and end bit ranges. Not really sure whats up with that.

[tylerbucher]

Might have an issue with dbc so triple checking first. Between SavvyCan this and my dbc file I have no clue which is doing this correct. Could definitely use a second set of eyes or insight on this.

[bit-dream]

@agent6262 Can you possibly provide me the DBC file you are using so I can look into this? Also, could you let me know which version of the library you are using? There was a bug in the decoding function at one point, but that (should of) been fixed at this point.

When I call the extractValFromPayload function directly, with the signal parameter you have above, I get an answer of 1:

// Input parameters, in order: payload, start bit, signal length, endian, signed
let val = can.extractValFromPayload([3, 65, 13, 55, 255, 255, 255, 255],8,4,'Motorola',false)
console.log(val)

returns val = 1

extractValFromPayload makes calls to extractBitRange, and a new start bit needs to be accounted for due to the difference in the endian of the message and the fact that there is a 'sawtooth' pattern that happens between the bytes because of the bit order of LSB to MSB. extractValFromPayload is called when using the decode method.

Do you have a code snippet that I could potentially run that would reproduce the error? I have a feeling there might be something going on upstream of the extractValFromPayload function since it returns 1 for the example you gave me.

[tylerbucher]

I apologize for the poor wite-up on my part was (3am my time 😅). when I run the test on my dbc file extractValFromPayload gets called like this can.extractValFromPayload([3, 65, 13, 55, 255, 255, 255, 255],11,4,'Motorola',false) not can.extractValFromPayload([3, 65, 13, 55, 255, 255, 255, 255],8,4,'Motorola',false). I am curious where / how you got to startbit 8 from 11?

I am on version 2.1.0 according to the package.json.

My DBC file (line 44)

VERSION ""


NS_ :
	NS_DESC_
	CM_
	BA_DEF_
	BA_
	VAL_
	CAT_DEF_
	CAT_
	FILTER
	BA_DEF_DEF_
	EV_DATA_
	ENVVAR_DATA_
	SGTYPE_
	SGTYPE_VAL_
	BA_DEF_SGTYPE_
	BA_SGTYPE_
	SIG_TYPE_REF_
	VAL_TABLE_
	SIG_GROUP_
	SIG_VALTYPE_
	SIGTYPE_VALTYPE_
	BO_TX_BU_
	BA_DEF_REL_
	BA_REL_
	BA_DEF_DEF_REL_
	BU_SG_REL_
	BU_EV_REL_
	BU_BO_REL_
	SG_MUL_VAL_

BS_:

BU_:

BO_ 2024 OBD2: 8 Vector__XXX
 SG_ S6base : 2|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S5base : 10|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S1_PID_0D_VehicleSpeed m13 : 31|8@0+ (1,0) [0|255] "km/h" Vector__XXX
 SG_ S1_PID_11_ThrottlePosition m17 : 31|8@0+ (0.39216,0) [0|100] "%" Vector__XXX
 SG_ SS1 m1M : 23|8@0+ (1,0) [0|255] "" Vector__XXX
 SG_ Service M : 11|4@0+ (1,0) [0|15] "" Vector__XXX

SG_MUL_VAL_ 2024 S1_PID_0D_VehicleSpeed SS1 13-13;
SG_MUL_VAL_ 2024 S1_PID_11_ThrottlePosition SS1 17-17;
SG_MUL_VAL_ 2024 SS1 Service 1-1;

BO_ 2348875518 ExtendedMultiplexMessage: 8 Vector__XXX
 SG_ S6base : 2|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S5base : 10|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S4base : 10|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S6 m2 : 2|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S5 m6 : 10|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S4 m5 : 10|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S3 m4 : 18|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S2 m4 : 10|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S1 m0M : 2|4@1+ (1,0) [0|0] "" Vector__XXX
 SG_ S0 M : 0|2@1+ (1,0) [0|0] "" Vector__XXX



BA_DEF_ BO_  "SingleFrame" INT 0 1;
BA_DEF_ SG_  "DDI" INT 0 65535;
BA_DEF_ SG_  "SigType" ENUM  "Default","Range","RangeSigned","ASCII","Discrete","Control","ReferencePGN","DTC","StringDelimiter","StringLength","StringLengthControl";
BA_DEF_ SG_  "GenSigEVName" STRING ;
BA_DEF_ SG_  "GenSigILSupport" ENUM  "No","Yes";
BA_DEF_ SG_  "GenSigSendType" ENUM  "Cyclic","OnWrite","OnWriteWithRepetition","OnChange","OnChangeWithRepetition","IfActive","IfActiveWithRepetition","NoSigSendType";
BA_DEF_ BO_  "GenMsgFastOnStart" INT 0 100000;
BA_DEF_ SG_  "GenSigInactiveValue" INT 0 0;
BA_DEF_ BO_  "GenMsgCycleTimeFast" INT 0 3600000;
BA_DEF_ BO_  "GenMsgNrOfRepetition" INT 0 1000000;
BA_DEF_ SG_  "GenSigStartValue" INT 0 10000;
BA_DEF_ BO_  "GenMsgDelayTime" INT 0 1000;
BA_DEF_ BO_  "GenMsgILSupport" ENUM  "No","Yes";
BA_DEF_ BO_  "GenMsgStartDelayTime" INT 0 100000;
BA_DEF_ BU_  "NodeLayerModules" STRING ;
BA_DEF_ BU_  "ECU" STRING ;
BA_DEF_ BU_  "NmJ1939SystemInstance" INT 0 15;
BA_DEF_ BU_  "NmJ1939System" INT 0 127;
BA_DEF_ BU_  "NmJ1939ManufacturerCode" INT 0 2047;
BA_DEF_ BU_  "NmJ1939IndustryGroup" INT 0 7;
BA_DEF_ BU_  "NmJ1939IdentityNumber" INT 0 2097151;
BA_DEF_ BU_  "NmJ1939FunctionInstance" INT 0 7;
BA_DEF_ BU_  "NmJ1939Function" INT 0 255;
BA_DEF_ BU_  "NmJ1939ECUInstance" INT 0 3;
BA_DEF_ BU_  "NmJ1939AAC" INT 0 1;
BA_DEF_ BU_  "NmStationAddress" INT 0 255;
BA_DEF_ BO_  "GenMsgSendType" ENUM  "cyclic","NotUsed","IfActive","NotUsed","NotUsed","NotUsed","NotUsed","NotUsed","noMsgSendType";
BA_DEF_ BO_  "GenMsgRequestable" INT 0 1;
BA_DEF_ BO_  "GenMsgCycleTime" INT 0 3600000;
BA_DEF_ SG_  "SPN" INT 0 524287;
BA_DEF_  "DBName" STRING ;
BA_DEF_  "BusType" STRING ;
BA_DEF_  "ProtocolType" STRING ;
BA_DEF_ BO_  "VFrameFormat" ENUM  "StandardCAN","ExtendedCAN","reserved","J1939PG";
BA_DEF_DEF_  "SingleFrame" 1;
BA_DEF_DEF_  "DDI" 0;
BA_DEF_DEF_  "SigType" "Default";
BA_DEF_DEF_  "GenSigEVName" "Env@Nodename_@Signame";
BA_DEF_DEF_  "GenSigILSupport" "Yes";
BA_DEF_DEF_  "GenSigSendType" "NoSigSendType";
BA_DEF_DEF_  "GenMsgFastOnStart" 0;
BA_DEF_DEF_  "GenSigInactiveValue" 0;
BA_DEF_DEF_  "GenMsgCycleTimeFast" 0;
BA_DEF_DEF_  "GenMsgNrOfRepetition" 0;
BA_DEF_DEF_  "GenSigStartValue" 0;
BA_DEF_DEF_  "GenMsgDelayTime" 0;
BA_DEF_DEF_  "GenMsgILSupport" "Yes";
BA_DEF_DEF_  "GenMsgStartDelayTime" 0;
BA_DEF_DEF_  "NodeLayerModules" "";
BA_DEF_DEF_  "ECU" "";
BA_DEF_DEF_  "NmJ1939SystemInstance" 0;
BA_DEF_DEF_  "NmJ1939System" 0;
BA_DEF_DEF_  "NmJ1939ManufacturerCode" 0;
BA_DEF_DEF_  "NmJ1939IndustryGroup" 0;
BA_DEF_DEF_  "NmJ1939IdentityNumber" 0;
BA_DEF_DEF_  "NmJ1939FunctionInstance" 0;
BA_DEF_DEF_  "NmJ1939Function" 0;
BA_DEF_DEF_  "NmJ1939ECUInstance" 0;
BA_DEF_DEF_  "NmJ1939AAC" 0;
BA_DEF_DEF_  "NmStationAddress" 254;
BA_DEF_DEF_  "GenMsgSendType" "noMsgSendType";
BA_DEF_DEF_  "GenMsgRequestable" 1;
BA_DEF_DEF_  "GenMsgCycleTime" 0;
BA_DEF_DEF_  "SPN" 0;
BA_DEF_DEF_  "DBName" "";
BA_DEF_DEF_  "BusType" "CAN";
BA_DEF_DEF_  "ProtocolType" "ISO11783";
BA_DEF_DEF_  "VFrameFormat" "J1939PG";
BA_ "DBName" "ExtendedMultiplexDbc";
BA_ "VFrameFormat" BO_ 2348875518 3;

SG_MUL_VAL_ 2348875518 S6 S0 2-2;
SG_MUL_VAL_ 2348875518 S5 S1 6-6;
SG_MUL_VAL_ 2348875518 S4 S1 5-5;
SG_MUL_VAL_ 2348875518 S3 S1 4-4;
SG_MUL_VAL_ 2348875518 S2 S1 4-4;
SG_MUL_VAL_ 2348875518 S1 S0 0-0, 1-1;

My test

test('DBC_SigMulVal.dbc: Decode Multiplex signal', (done) => {
  const dbc = new Dbc();
  const fileContent = dbcReader('src/__tests__/testFiles/DBC_SigMulVal.dbc');
  const data = dbc.load(fileContent);
  const can = new Can();
  can.database = data;
  const frame = can.createFrame(2024, [3, 65, 13, 55, 255, 255, 255, 255]);
  const bndMsg = can.decode(frame);
});

[mi-hol]

@tylerbucher did the fix work, so this issue could be closed?

[tylerbucher]

The changes to fix the issue I was seeing was rolled back and not included in the PR. At this time I will close this issue, but I am unsure if this issue was actually resolved or not.