[Discuss-gnuradio] UHD USRP Sink Stream Tagging

[Alex Teo]

Hello all,

I have been trying to implement a custom block based on
gr_message_source that will be connected to the UHD USRP sink block.
It inserts tx_sob and tx_eob tags together with the message contents
into the output stream. I have a few questions with regards to the
proper use of the tx streaming tags after looking at the source code
for both the C++ tags demo as well as the USRP sink:

1. I see that in the tags demo code (specifically tag_source_demo.h)
that a tx_eob tag is first sent when the block starts running (as
_samps_left_in_burst is set to 1 initially). Is there any reason
behind this?

2. Looking at the USRP sink code, it seems that I can just insert
tx_sob and tx_eob tags without having to insert a tx_time tag together
with a tx_sob tag?

3. Am I right in my understanding that the USRP2 will only start
transmitting after receiving an tx_eob tag? If so, I presume that
there's a limit as to how much data the USRP2 can buffer before
transmitting?

Thank you.

Regards,
Alex Teo