JEK changes enabling proper recording of IMU/GPS datastrams - 02-APR-2013
Fork of GPS_Incremental by
Diff: OEM615.h
- Revision:
- 9:b45feb91ba38
- Parent:
- 6:2a8486283198
--- a/OEM615.h Wed Apr 17 13:50:21 2013 +0000 +++ b/OEM615.h Fri Apr 19 16:21:27 2013 +0000 @@ -3,24 +3,26 @@ //set up the GPS message header in a structure to enable easy reading -- see the OEM615 manual (Table 4, page 24) struct MESSAGEHEADER { - char synchAA; //1st synch word - char synch44; //2nd synch word - char synch12; //3rd synch word - unsigned char headerLength; //always 28 - unsigned short messageID; //42 (BESTPOS) , 43 (RANGE) , or 99 (BESTVEL), - char messageType; //always = 0 for binary - unsigned char portAddress; //0x20 for COM1 - unsigned short messageLength; //not including header or CRC - unsigned short sequence; //typically 0 - unsigned char idleTime; //Time the processor is idle, in the last second - unsigned char timeStatus; //Enum Indicating quality of the GPS reference time - unsigned short GPSweek; //GPS reference week - unsigned long GPSTime_msecs; //from beginning of week - unsigned long receiverStatus; //32-bits representing the status of hardware and software + char synchAA; //1st synch word + char synch44; //2nd synch word + char synch12; //3rd synch word + unsigned char headerLength; //always 28 + unsigned short messageID; //42 (0x2A BESTPOS) , 43 (2B RANGE) , or 99 (x63 BESTVEL), + char messageType; //always = 0 for binary + unsigned char portAddress; //0x20 for COM1 + // from spec: The length in bytes of the body of the message, not including the header nor the CRC + unsigned short messageLength; //not including header or CRC + unsigned short sequence; //typically 0 + unsigned char idleTime; //Time the processor is idle, in the last second + unsigned char timeStatus; //Enum Indicating quality of the GPS reference time + unsigned short GPSweek; //GPS reference week + unsigned long GPSTime_msecs; //from beginning of week + unsigned long receiverStatus; //32-bits representing the status of hardware and software unsigned short reserved; unsigned short receiverSWversion; //receiver software build number + //total length in bytes of this header is 28 }; -MESSAGEHEADER *msgHeader[4]; +MESSAGEHEADER *msgHeader[6]; #pragma pack(1) //structure for OEM615 BESTVEL log message (page 314) @@ -113,11 +115,23 @@ const unsigned char maxGPSMessagesPerSec = 12; unsigned short messageLocation[maxGPSMessagesPerSec] = {0}; //stores the message location start within the message buffer +unsigned short bytesFromMessageHdrDetect = 0; +union SWAPBYTES { unsigned char b[2]; unsigned short w; }; +volatile SWAPBYTES messageLength; //used to swap the bytes +unsigned long computedCRC = 0; //final resulting computed CRC for this message +unsigned long incrementalCRC = 0; //incrementally-formed CRC over message sequence +unsigned short endByteForCRCcomputation = 0; +bool completeMessageAvailable = false; + //this code was taken from the Novatel Firmware document page 35 -#define CRC32_POLYNOMIAL 0xEDB88320L +//#define CRC32_POLYNOMIAL 0xEDB88320L /* -------------------------------------------------------------------------- Calculate a CRC value to be used by CRC calculation functions. -------------------------------------------------------------------------- */ +/* +//////////////////////////////////////////// +//original code from the OEM615 manual +//////////////////////////////////////////// unsigned long CRC32Value(int i) { int j; @@ -132,15 +146,53 @@ } return ulCRC; } +*/ + +#define CRC32_POLYNOMIAL 0xEDB88320L +void CRC32Value(unsigned long &CRC, unsigned char c) +{ + ///////////////////////////////////////////////////////////////////////////////////// + //CRC must be initialized as zero + //c is a character from the sequence that is used to form the CRC + //this code is a modification of the code from the Novatel OEM615 specification + ///////////////////////////////////////////////////////////////////////////////////// + unsigned long ulTemp1 = ( CRC >> 8 ) & 0x00FFFFFFL; + unsigned long ulCRC = ((int) CRC ^ c ) & 0xff ; + for (int j = 8 ; j > 0; j-- ) + { + if ( ulCRC & 1 ) + ulCRC = ( ulCRC >> 1 ) ^ CRC32_POLYNOMIAL; + else + ulCRC >>= 1; + } + CRC = ulTemp1 ^ ulCRC; +} /* -------------------------------------------------------------------------- Calculates the CRC-32 of a block of data all at once -//the CRC is c from the complete message (header plus data) but excluding (of course) the CRC at the end +//the CRC is from the complete message (header plus data) +//but excluding (of course) the CRC at the end -------------------------------------------------------------------------- */ unsigned long CalculateBlockCRC32( unsigned long ulCount, /* Number of bytes in the data block */ unsigned char *ucBuffer ) /* Data block */ { + ////////////////////////////////////////////////////////////////////// + //the below code tests the CRC32Value procedure used in a markov form + ////////////////////////////////////////////////////////////////////// + unsigned long CRC = 0; + for (int i = 0; i<ulCount; i++) CRC32Value( CRC, *ucBuffer++ ); + return CRC; +} + +/* +unsigned long CalculateBlockCRC32( + unsigned long ulCount, + unsigned char *ucBuffer ) +{ +//////////////////////////////////////////// +//original code from the OEM615 manual +//////////////////////////////////////////// unsigned long ulTemp1; unsigned long ulTemp2; unsigned long ulCRC = 0; @@ -152,8 +204,7 @@ } return( ulCRC ); } - - +*/ void sendASCII(char* ASCI_message, int numChars) { ///////////////////////////////////////////////// @@ -178,24 +229,46 @@ //MODSERIAL is an easy to use library that extends Serial to add fully buffered input and output. void readSerialByte(MODSERIAL_IRQ_INFO *q) { - MODSERIAL *serial = q->serial; - unsigned char synch0 = serial->getc(); + MODSERIAL *serial = q->serial; //see example of MODSERIAL usage in cookbook + unsigned char synch0 = serial->getc(); //get the next byte + + //byteCounter is zeroed only at a 1PPA event in the 1PPS ISR + //all message bytes stored for a single GPS second msgBuffer[byteCounter % maxGPSbytesPerSec] = synch0; + + //accumulate the CRC for this message + //incrementalCRC re-initialized after message header is is detected + CRC32Value( incrementalCRC, synch0); - //we need to trap the GPS message header byte-string 0xAA44121C + //Trap the GPS message header byte-string per Novatel OEM615 spec: 0xAA44121C //generate a 4-byte sliding-window sequence from the input bytes - //shift last 4-byte value left 8 bits & push recently read byte (synch0) into low-order byte - test = (test<<8) | synch0; // + //shift last 4-byte value left 8 bits & push current-read byte (synch0) into low-order byte + test = (test<<8) | synch0; if (test == 0xAA44121C) //test for the Receiver message header signature { - messageLocation[perSecMessageCounter % maxGPSMessagesPerSec] = byteCounter-3; //store the location of this message (with 4 synch words) - perSecMessageCounter++; - messageDetected = true; - } + messageLocation[perSecMessageCounter % maxGPSMessagesPerSec] = byteCounter-3; //store the location of this message (1st of 4 synch word) + perSecMessageCounter++; //counts messages this second + bytesFromMessageHdrDetect = 0; //start byte counter for this message + incrementalCRC = 0x39b0f0e1; //initializes the recursive CRC after the AA44121C header byte sequence + } + else if (bytesFromMessageHdrDetect == 5) messageLength.b[0] = synch0; //first byte of msg length + else if (bytesFromMessageHdrDetect == 6) //second byte of message length + { + messageLength.b[1] = synch0; + endByteForCRCcomputation = 24 + messageLength.w; //use union to perform byte-swap from stored bytes + } + else if (bytesFromMessageHdrDetect == endByteForCRCcomputation) //stop the CRC recursive computation + computedCRC = incrementalCRC; //store the computed CRC for this message for use in main + else if (bytesFromMessageHdrDetect == (endByteForCRCcomputation + 4) ) //detect the end of the message (end of its CRC) + { + savedMessageCounter = perSecMessageCounter; //message counter can be corrupted before use in main + completeMessageAvailable = true; //set flg for the main message processing + } + //byteCounter reset to zero in main after the 1PPS is detected -- its NOT reset in the 1PPS ISR byteCounter++; //total per-sec byte counter (reset to zero in main when 1PPS detected) - + bytesFromMessageHdrDetect++; //counts the byes received after a message header };