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[Discuss-gnuradio] inband pings and clock

From: George Nychis
Subject: [Discuss-gnuradio] inband pings and clock
Date: Fri, 03 Aug 2007 11:12:30 -0400
User-agent: Thunderbird (X11/20070604)

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.

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:


- George

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