I'm using the file_meta_sink to record time-stamped data, and I have a question
about the implementation of this block. I currently call it in Python as
follows:
self.blocks_file_meta_sink_0 = blocks.file_meta_sink(gr.sizeof_short*2,
self.dat_filename, samp_rate, 1, blocks.GR_FILE_SHORT, False, 2*int(samp_rate),
"", False)
If I understand the parameters right, I have configured this block so as to not
include extra header information.
If I also understand correctly, there are (by default, if no extras) eight
fields provided in the header.
However, when I run my Python flowgraph and read the header information from
the created file using gr_read_file_metadata.py, I get the following:
HEADER 0
Version Number: 0
Sample Rate: 10000000.00 sps
Seconds: 1381406414.235846
Item size: 4
Data Type: short (1)
Complex? False
Header Length: 171 bytes
Extra Length: 22
Extra Header? True
Size of Data: 80000000 bytes
20000000 items
Extra Header:
rx_freq:
8.99e+08
As you can see, a ninth field is returned as an extra header, rx_freq. As far
as I can tell in my flowgraph, I'm not doing anything myself that would cause
this field to be added. I'd like to know where this field is added since I'd
like to add more. Specifically I'd like to add a GPS string or two to tag
location and velocity. I'm using a USRP N210 with GPSDO and querying the
GPGGA, GPRMC, and XYZSP strings to get this information. I can currently parse
these strings and write what I want from them to another file, but if I can
contain it all in one file it would be easier for me to deal with off-line.
Thanks,
Scott Bennett
JHU/APL
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