Wavecom W-SPECTRA (Automatic Monitoring System) V1.1.0 - Manual (Page 251)

WAVECOM Monitoring System W-SPECTRA, W-SPEED Manual V1.1.0 WAVECOM Data Formats

241
Element Type Description
Sync int32 Synchronization number 0xa1b2c3d4.
Type int32 Derived from the chunk name, e.g., "SOFH", " EOFH", "SSIQ".
Size int32 The number of data bytes in the remainder of the chunk The value of size must be a mul-
tiple of 4.
Data byte[size] The chunk data in a format specific to the type.
 The maximum amount of data in a chunk is limited to 65536 bytes. This limits the separation be-
tween sync patterns.
 The length of each chunk must contain an integral number of 32 bit words even though the size
element in the chunk header is specified as a number of bytes.
 The PXGF format supports both little and big endian byte ordering, although it may be necessary
to provide the stream reader with the endian used depending on its implementation. The endian
format for a file or stream may be determined by reading the sync pattern. It is not permissible to
mix chunks of different endian format within a stream or file.
 When the PXGF format is used to store information in a file, there must be a global header at the
beginning of the file to aid identification of the file format and the data stored in the file. This is
necessary due to the potentially large size of files.
 Nested sub-chunks are not supported as this would unnecessarily complicate synchronization.
 The implication of the previous point is that all chunks are at root level and are interpreted entirely
sequentially. The parser must know which chunks need to be identified before it can use other
chunks. The only constraint here is that files must start with a “SOFH chunk”. Due to the sequen-
tial nature of parsing and the inability to nest chunks, a separate global chunk is needed to identi-
fy the end of the file header, namely the “EOFH” chunk.
APPLICATION NOTES
Above is a graphical illustration showing how PXGF chunks of different type are ordered in a stream/file.
Below are some notes to the developer to keep in mind when using the PXGF format in an application.
PXGF Chunk format. Cross section of typical stream.
 The PXGF framework for streaming and storage is designed to be extensible. Different applications
require different information and if this information is not available in a stream, then that applica-
tion will not be able to process that stream successfully. Just because an application uses the
PXGF format doesn't mean that it will be able to process all PXGF streams or files. For a particular
project care should be taken to ensure that all necessary chunks are included.
 It is recommended that meta data like the sample rate and packing description be sent every sec-
ond. This allows state information to be recovered if synchronization is lost and makes it possible
to process large files from the middle of the file.
 Only data from one data source and of one format must be included in each stream or file. Current
formats include “SSIQ” for single channel data and “GSIQ” for multi-channel data. The format