Thanks for all your help. Here's a semantics question. It seems that CRC
is "frame level" as you said, but when I look at the code for serialP.nc, it
looks like the CRC is only done on the packet level. That is... the CRC is
calculated, then the byte is sent to the "frame layer" where an extra escape
character (0x7d) can be placed into the stream (see code snippet below).
SerialFrameComm.putData(txBuf[txIndex].buf) seems to call the
HdlcTranslateC.nc putData which adds the escaped sequence, when necessary.
If CRC is truly a frame CRC, the CRC calculation should include the escape
byte for escaped data, in my humble opinion.
case TXSTATE_INFO:
atomic {
txResult = call SerialFrameComm.putData(txBuf[txIndex].buf);
txCRC = crcByte(txCRC,txBuf[txIndex].buf);
++txByteCnt;
if (txIndex == TX_DATA_INDEX){
uint8_t nextByte;
nextByte = signal SendBytePacket.nextByte();
if (txBuf[txIndex].state == BUFFER_COMPLETE || txByteCnt >=
SERIAL_MTU){
txState = TXSTATE_FCS1;
}
else { /* never called on ack b/c ack is BUFFER_COMPLETE
initially */
txBuf[txIndex].buf = nextByte;
}
}
else { // TX_ACK_INDEX
txState = TXSTATE_FCS1;
}
}
break;
Your thoughts?
Regards,
Kurt
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