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Diffstat (limited to 'host/docs')
| -rw-r--r-- | host/docs/sync.rst | 42 |
1 files changed, 31 insertions, 11 deletions
diff --git a/host/docs/sync.rst b/host/docs/sync.rst index a33fa134d..15f3b10cf 100644 --- a/host/docs/sync.rst +++ b/host/docs/sync.rst @@ -21,11 +21,11 @@ USRPs take two reference signals in order to synchronize clocks and time. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Provide reference signals ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -Most USRPs have front panel SMA connectors to source these signals externally. -Alternatively, some USRP models support an optional internal GPSDO. -Typically, these signals are provided from a GPSDO. +Most USRPs have front panel SMA connectors to source these reference signals. +Typically, these signals are provided by an external GPSDO. +Some USRP models can provide these signals from an optional internal GPSDO. For user's generating their own signals, -the pulse-per-second should be clocked off of the 10MHz reference. +the pulse-per-second should be clocked from the 10MHz reference. See the application notes for your device for specific signal requirements. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -98,21 +98,41 @@ The user can query the gps_time sensor to wait for the NMEA string. usrp->set_time_next_pps(uhd::time_spec_t(gps_time+1)); ------------------------------------------------------------------------ -Synchronizing multiple channels +Synchronizing channel phase ------------------------------------------------------------------------ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -Synchronizing the cordics +Align CORDICs in the DSP ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The frequency translation between baseband and IF can introduce a phase ambiguity between channels. This is due to the property that the cordic in the DSP chain can have a random phase offset. -Fortunately, the cordic is reset on each start-of-burst. +Fortunately, the CORDIC is reset on each start-of-burst. Therefore, the method to phase-align the cordics is to coordinate streaming at a particular time. -For receive, a burst is started when the user issues a stream command. This stream command should have a time spec set. -For transmit, a burst is started when the user calls send. The metadata should have a time spec and start of burst set. +* For receive, a burst is started when the user issues a stream command. This stream command should have a time spec set. +* For transmit, a burst is started when the user calls send. The metadata should have a time spec and start of burst set. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -Synchronizing the RF LOs +Align LOs in the front-end ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - +After tuning the RF front-ends, +each local oscillator will have a random phase offset. +Some daughterboards have mechanisms to phase-align the oscillators, +however, these mechanisms are not currently implemented. +In any case, LO phase-alignment will not forgo the need for calibration. + +**RX Calibration** + +1) Tune the setup. +2) Receive known signals. +3) Capture calibration data. +4) Do not re-tune. +5) Receive live data. + +**TX Calibration** + +1) Tune the setup. +2) Transmit known signals. +3) Capture calibration data. +4) Do not re-tune. +5) Transmit live data. |