Minor "bug" (doesn't exhibit) and CRC question

[conoror]

This isn't a bug per se but it might become one (it's by code inspection)

On line 1711 on MFRC522.cpp there is a set of validBits to 8. It should be 0:

validBits = 8;
status = PCD_TransceiveData(&cmd, (byte)1, response, &received, &validBits, (byte)0, false); // 43

if you do this, the code in PCD_CommunicateWithPICC (line 436) which reads:

byte bitFraming = (rxAlign << 4) + txLastBits;		// RxAlign = BitFramingReg[6..4]. TxLastBits = BitFramingReg[2..0]

will attempt to set BitFramingReg[3] to 1. Now that bit is reserved so nothing bad actually happens!

Question about the same routine (PCD_CommunicateWithPICC). On line 501 there is a check to see if you have at least 2 bytes before calling CRC. Which, if you have exactly 2 bytes, will result in calling the CRC with zero data. I've no idea if this a bad idea... perhaps it is just fine and will return the CRC initialisation value. Just wondering :-)

[me21]

Now there is less than 1700 lines in MFRC522.cpp and I cannot find such code snippet.
So the only relevant part of this issue is the question about CRC.

[Rotzbua]

@me21 you have to look at the release branch https://github.com/miguelbalboa/rfid/blob/release_1_4_X/src/MFRC522.cpp
At the master I separated the file into smaller peaces to increase maintainability.