Rowe HASCP, Operation Manual

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7.4 Data Structure ID list
These codes are used to identify the data structure types contained in the Output Data.
0. SYSTEM_CHECKSUM
1. SYSTEM_LEADER
2. VERTICAL_STAGE
3. HORIZONTAL_JANUS_LEADER
4. HORIZONTAL_JANUS_GOOD
5. HORIZONTAL_JANUS_BEAM
6. HORIZONTAL_JANUS_INSTRUMENT
7. HORIZONTAL_JANUS_AMPLITUDE
8. HORIZONTAL_JANUS_CORRELATION
9. BACKSCATTER_LEADER_00
10. BACKSCATTER_PROFILE_00
11. BACKSCATTER_LEADER_01
12. BACKSCATTER_PROFILE_01
13. BACKSCATTER_LEADER_02
14. BACKSCATTER_PROFILE_02
15. BACKSCATTER_LEADER_03
16. BACKSCATTER_PROFILE_03
17. BACKSCATTER_LEADER_04
18.
BACKSCATTER_PROFILE_04
7.5 Ensemble Output Data Structure (little endian)
Data structures contained in the output data are stored as a linked list. Each data structure has 4 bytes
at the beginning containing the ID and Size (bytes in the structure). The structure data begins at the
next byte after the Size. To find the ID address of the next linked structure add the current Size to the
next address after the current Size.
Each ensemble has a wrapper and a payload. The wrapper has an 8 byte header to help identify the
start of ensemble. After the header the payload size, in bytes, is used to locate the end of the ensemble
where the checksum is stored. An inverted payload size is included to help check data integrity.
The payload checksum is calculated using code shown below.
unsigned short rtiprocA_CRCcalc ( void * data , int len )
{
unsigned char * dataPtr = ( unsigned char *) data ;
int index = 0;
unsigned short crc = 0;
while ( len --)
{
crc = ( unsigned char )( crc >> 8) | ( crc << 8);
crc ^= dataPtr [ index ++];
crc ^= ( unsigned char )( crc & 0xff) >> 4;
crc ^= ( crc << 8) << 4;
crc ^= (( crc & 0xff) << 4) << 1;
}
return crc ;
}
If the ensemble checksum matches the calculated check sum and the inverted payload size matches
the payload size inverted, the ensemble data is considered to be valid.