[Discuss-gnuradio] usrp1_source_base, usrp_standard_rx::read, and 512 nbytes

[Chris Stankevitz]

usrp1_source_base.cc has this chunk of code that reads from 
usrp_standard_rx:

//----------
while (output_index < noutput_items)
{
  int nbytes = ninput_bytes_reqd_for_noutput_items (
    noutput_items - output_index);

  nbytes = std::min (nbytes, BUFSIZE);

  int result_nbytes = d_usrp->read (buf, nbytes, &overrun);
//----------

Question: What guarantees that nbytes is a multiple of 512?

According to usrp_basic.h, nbytes must be a multiple of 512.  It seems 
to me that nouput_items would need to be specially crafted upstream so 
that nbytes is a multiple of 512.

Thank you,

Chris