Re: [Discuss-gnuradio] inband timestamp issues

[George Nychis]

Hi Steve,

> We certainly appreciate the work you've done (along with Thibauld et
> al.) towards the inband functionality!

Thanks!  It's been a major group effort along with Eric, Thibaud, Leo, 
and Brian.


> Anyway, we've found a solution that seems to work, although I'm having
> troubles testing it thoroughly.  Basically, instead of having both the
> interleaving and non-interleaving functionalities available in the
> same rbf, we have made a new rbf that has all the USB packet/timestamp
> functionality but assumes symbol interleaving.  For our applications,
> we don't anticipate needing the flexibility of independent transmit
> channels.

Okay, this sounds like a reasonable solution.  I think that multiple 
RBFs is not a bad thing.  Especially since its a functionality that is 
quite exclusive... i don't think its something you're likely to turn off 
and on in a single application.  You should be able to do the 
interleaving at the host easily.

> We're currently in the stage of writing the host code for using
> multiple USRPs.  Previously, we had host code written to use the
> inband_2rxhb_2tx.rbf with both transmit and receive on a single USRP,
> and this was relatively successful.  Our current strategy is a little
> ugly; we're modifying the inband code so that multiple USRPs are
> controlled with a single usrp_server.  I realize this is not how the
> code was meant to be utilized, but we've got concerns about sending
> data (which is supposed to be transmitted simultaneously) to two
> independent usrp_servers and having them both arrive on time.  This
> concern is exacerbated by a demo next month where we hope to use 4x4.
> So we are taking the safer, yet messier, route for the moment.

hmmmm yeah, it was meant to be 1 usrp_server to 1 usrp.  I'm not sure 
you really need to do this.  You just need to make sure that both USRP's 
clocks are synchronized.  From that, the timestamp (which currently has 
some issues) should allow you to transmit simultaneously on both.

> Anyway, I wanted to give you (and the list in general) a status update
> and let you know that we'll be happy to collaborate on anything
> regarding the inband code.  Feel free to contact me and/or Ketan
> outside of the list as well.

Thanks Steve!  I will probably keep in contact with you so that you can 
test some updates we have on the timestamp issue you found.  I'm about 
to send another mail to the list about this.

- George