[Discuss-gnuradio] Underrun when transmitting long packets

[Ramazan Cetin]

Hello all,

I am transmitting TAP packets using USRP E310 in network mode. I have a 
custom block called "rtag" which gets two TAP interface inputs and puts 
these messages to output (it's serializing these inputs). I am tagging 
each packet with "packet_len"(beginning of packet) and "tx_eob"(end of 
packet). This is a general_block. It receives a message for detecting 
which input has a tagged stream data. According to this message, it 
configures its forecast() method.

There is no problem by transmitting short packets. But when i send long 
packet to USRP it gives "U" letter. There is a log in below:

----------------------------------------------------------------------
Tag Debug: TX_OFDM_TAP0
Input Stream: 00
  Offset: 100290  Source: n/a     Key: packet_len   Value: 1950
----------------------------------------------------------------------
ninput_items: 1950
input[0]: ninput_items[]: 1950, nitems_read(): 100290, noutput_items: 1024
ninput_items[!i]: 0current direction: 0next direction: 100

----------------------------------------------------------------------
Tag Debug: TX_OFDM_FINAL
Input Stream: 00
  Offset: 208330  Source: n/a     Key: packet_len   Value: 1950
  Offset: 210279  Source: rtag     Key: tx_eob   Value: #t
----------------------------------------------------------------------
----------------------------------------------------------------------
Tag Debug: TX_OFDM_TAP0
Input Stream: 00
  Offset: 102240  Source: n/a     Key: packet_len   Value: 8670
----------------------------------------------------------------------

ninput_items: 1950

input[0]: ninput_items[]: 8670, nitems_read(): 102240, noutput_items: 4096
ninput_items[!i]: 0current direction: 0next direction: 100

----------------------------------------------------------------------
Tag Debug: TX_OFDM_FINAL
Input Stream: 00
  Offset: 212230  Source: n/a     Key: packet_len   Value: 8670
----------------------------------------------------------------------
U
----------------------------------------------------------------------


As you can observe, after sending packet with size of 8670 items, it 
prints "U" and this packet cannot transmit to other side.

Another point is, in "TX_OFDM_FINAL" tag debug, i cannot see "tx_eob" 
tag. I guess full packet cannot be transmitted to the output by gnuradio.

What is the problem in here?

There is a FG and impl.cc code of my custom block "rtag" in the attachments.

Best regards.

ofdm_rtag_test.grc
Description: XML document

rtag_impl.cc
Description: Text Data