Thanks Dave, Great ideas.
Eric On Mon, Feb 26, 2007 at 05:32:19PM -0500, David I. Emery wrote: > On Sun, Feb 25, 2007 at 03:56:07PM -0800, Eric Blossom wrote: > > Would those of you with an interest in USRP inband signaling, please > > take a look at the latest proposed packet format. Now's a good time > > to change things ;) > > I might have more comments later, but one function that would be > very nice to have implemented in the FPGA/in band signaling code would > be the ability to capture the count in the rolling 64 MHz counter on one > edge (perhaps a selectable edge selected by a bit in a config register > somewhere) of an external input signal available to the user via an IO > pin and save that value in a register that could be read through the in > band signaling mechanisms (or perhaps alternatively, automatically > exported in the sample stream as a TIME_STAMP out of band message as > soon as convenient after the edge happens). > > This would allow use of global tick signals such as 1 PPS from a > GPSDO or GPS receiver to both synchronize a USRP sample stream (or > streams from a cluster of multiple USRPs) to absolute (or at least > global to a whole site) epochs in time, and for an accurate stable 1 PPS > to be used to measure the moment to moment 64 MHz clock frequency offset > allowing more or less auto-magical correction of all the various > frequencies derived from this clock in the tune code and elsewhere. > > Of course a future, more advanced USRP might also include > provisions for locking the master clock (which has to be very very clean > for optimum phase noise performance, particularly in aliased type > sampling of higher than nyquist IFs and thus cannot all that easily be > generated externally and piped around) to the universal standard 10 MHz > reference frequency readily available from cheap and easily obtained > GPSDOs. At the very least providing an easy way of using a VCXO > instead of just a cheap TCXO without cutting up the etch would help, > even if the DAC and LPF required to sync it was external. > > > -- > Dave Emery N1PRE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass 02493 > "An empty zombie mind with a forlorn barely readable weatherbeaten > 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in > celebration of what could have been, but wasn't and is not to be now either." _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
