[Discuss-gnuradio] problem with streamed tags

[Mat Mat]

hi all,

I have three blocks:

1. MESSAGE_LOADER
reads a binary file and outputs it byte by byte to the next block
(PACKET_CREATOR). On every 28th byte (and on the 0th byte) it adds tags
denoting the start of a PDU

2. PACKET_CREATOR (tagged_stream_block)
waits for 28 bytes to arrive. once this is accomplished, it reads the
first of those 28 bytes and uses it for internal logic. the other 27
bytes are the payload of a packet, to which it prepends a header and
appends a crc (2 bytes). NOTE: the length of the header in bits is not
divisible by 8. because of this, in order to have the whole packet in
one single chunk of memory, I have to do tedious bit shifting of the 27
payload bytes that come after the header.. once the packet is created, I
want to pass it to the next block, containing tags in the first header
byte. So, now I've changed things: before, the tags were 'connected' to
the first payload byte. now, I want them to be 'connected' to the first
header byte, which was created in this very block.

3. PACKET_VERIFIER (tagged_stream_block)
for testing purposes, I want this block to receive the whole packet that
was created in PACKET_CREATOR and write it to the screen. In order for
the block to know when a packet starts, every first byte of a packet
must contain the length of it.

My question is this: I don't get this item enumeration thing in
gnuradio. between the first 2 blocks it was easy enough, as I had to
simply include tags in every 28th byte, and it is easy to picture item
enumeration there (the first byte of the file has offset 0, the second
one 1 etc). but how are the items enumerated between the PACKET_CREATOR
and the PACKET_VERIFIER block?? which item index should I use to add the
length tag to the first header byte??

I hope I have made myself sufficiently clear..if not, feel free to ask
for more details. any help is immensely appreciated!

thanks in advance!

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