[Discuss-gnuradio] missing length tag

[cdl]

hello
i write a grc,i use the virtual sink and virtual source,the grc woked well
when i replace the virtual sin and source with usrp sink and source,there is a problem occured
the message is:

gr::log :FATAL: repack_bits_bb0 - Missing a required length tag on port 0 at item #0

thread[thread-per-block[10]: <block repack_bits_bb (10)>]: Missing length tag.

i have set the block (repack bits)'s parameter length tag key  == "tsb_tag",
but what this message "missing length tag" mean,
thank you

这个十一，“邮”我们，请尽情享受在路上的心情。-马上装备网易邮箱大师

chat_app.grc
Description: Binary data