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Re: [Discuss-gnuradio] Parsing extra metadata

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Parsing extra metadata
Date: Thu, 21 Aug 2014 19:18:08 -0400

On Thu, Aug 21, 2014 at 6:16 PM, Daniel Marlow <address@hidden> wrote:
Hi Tom,

  Thanks for looking at this.   The answer is "yes," as can be seen from the output below.     The rx_freq field is not something that I added.   I did add the "dumm" field, however.  

Dan Marlow

address@hidden:~/pulsar/DAQ$ gr_read_file_metadata meta_test.dat.hdr
Version Number: 0
Sample Rate: 4000000.00 sps
Seconds: 0.184295
Item size: 4
Data Type: float (5)
Complex? False
Header Length: 189 bytes
Extra Length:  40
Extra Header?  True
Size of Data: 65536 bytes
              16384 items

Extra Header:

Ok, so that's good. Looks like the basic concept is working fine, then. The rx_freq field is coming from the USRP. The UHD sends tags with information about the settings, which get stored in the metadata files. If you change the frequency, it'll generate another tag for you.

It looks like you should look into the gr_read_file_meatadata app to see how it's using the parse_metadata. That might clue you into what's going wrong in your project.


On Aug 21, 2014, at 6:03 PM, Tom Rondeau wrote:

On Tue, Aug 19, 2014 at 3:13 PM, Daniel Marlow <address@hidden> wrote:

   I am trying to add some extra information to the standard metadata file header.    

   Following the information posted on http://gnuradio.org/doc/doxygen/page_metadata.html , I am able to write and read the standard metadata.    I have attempted to add extra metadata with the following lines in my flowgraph:

                # add some extra meta data
key = pmt.pmt_intern("dummy")
val = pmt.pmt_from_long(77) 
extras = pmt.pmt_make_dict()
extras = pmt.pmt_dict_add(extras, key, val)
extras_str = pmt.pmt_serialize_str(extras)

                nItems = 1024*size
self.blocks_file_meta_sink_0 =  blocks.file_meta_sink(gr.sizeof_float*1,"./meta_test.dat",
  samp_rate, 1, blocks.GR_FILE_FLOAT, False, nItems, extras_str, True)

  I think that the writing is going OK, since the length of the header increases by a reasonable amount and a Unix hexdump indicates that the "dummy" data is present.   However, I am stuck when it comes to getting at the extra data using the parse_file_metadata functions.  In particular, when I try to read the data using:

        cHeader = c[0:185]   # character array read from file 
    pmt_dict = pmt.pmt_deserialize_str(cHeader) 
    p = parse_file_metadata.parse_header(pmt_dict,False)
    p_extra = parse_file_metadata.parse_extra_dict(pmt_dict,info,True)
The first parse_file_metadata line successfully provides the standard metadata, but the second parse_file_metadata does not provide the extra "dummy" data.   I suspect that it has to do with my poor understanding of what should go in the info argument.

Any help would be greatly appreciated.

Dan Marlow


What happens when you run gr_read_metadata on the file that's created? Does that show your extra header info?


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