[Discuss-gnuradio] inband pings and clock

[George Nychis]

What is 'pingval' and what is its units?  I didn't think most pings had 
a value, only empty responses for which you could compute whatever delay 
value you please by calculating the time between.
http://gnuradio.org/trac/browser/gnuradio/branches/developers/gnychis/inband/usrp/host/lib/inband/usrp_server.mbh#L105

Second question.  For an application to properly timestamp outgoing 
packets, the application needs some general idea of the current clock 
value on the USRP.  At first I was thinking "oh well the app can just 
send a ping and read the timestamp off of the response while calculating 
the delay."  Well, the ping doesn't carry the clock back up to the 
application.  RX packets (response-recv-raw-samples) carry the timestamp 
back up to the application, but there is no notion of calculating delay 
here.

Is the clock stored in a readable register somewhere on the USRP that a 
register read could be used?  The delay could be calculated here between 
the request and response.  I checked our wiki but see no register:
http://gnuradio.org/trac/wiki/UsrpFPGA

Thanks!

- George