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| -rw-r--r-- | host/docs/general.rst | 62 |
1 files changed, 61 insertions, 1 deletions
diff --git a/host/docs/general.rst b/host/docs/general.rst index 73b820c84..ff85fb0f9 100644 --- a/host/docs/general.rst +++ b/host/docs/general.rst @@ -5,7 +5,63 @@ UHD - General Application Notes .. contents:: Table of Contents ------------------------------------------------------------------------ -Misc notes +Tuning notes +------------------------------------------------------------------------ + +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +Two-stage tuning process +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +A USRP device has two stages of tuning: + +* RF front-end: translates bewteen RF and IF +* DSP: translates between IF and baseband + +In a typical use-case, the user specifies an overall center frequency for the signal chain. +The RF front-end will be tuned as close as possible to the center frequency, +and the DSP will account for the error in tuning between target frequency and actual frequency. +The user may also explicitly control both stages of tuning through the tune_request_t object. + +Pseudo-code for tuning the receive chain: +:: + + //tuning to a desired center frequency + usrp->set_rx_freq(my_frequency_in_hz); + + --OR-- + + //advanced tuning with tune_request_t + uhd::tune_request_t tune_req; + tune_req.target_freq = my_frequency_in_hz; + //fill in tune request fields... + usrp->set_rx_freq(tune_req); + +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +RF front-end settling time +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +After tuning, the RF front-end will need time to settle into a usable state. +Typically, this means that the local oscillators must be given time to lock before streaming begins. +Lock time is not consistent; it varies depending upon the device and requested settings. +After tuning and before streaming, the user should +wait for the "lo_locked" sensor to become true, +or sleep for a conservative amount of time (perhaps a second). + +Pseudo-code for dealing with settling time after tuning on receive: +:: + + usrp->set_rx_freq(...); + sleep(1); + usrp->issue_stream_command(...); + + --OR-- + + usrp->set_rx_freq(...); + while (not usrp->get_rx_sensor("lo_locked").to_bool()){ + //sleep for a short time in milliseconds + } + usrp->issue_stream_command(...); + +------------------------------------------------------------------------ +Threading notes ------------------------------------------------------------------------ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -46,6 +102,10 @@ Add the following line to */etc/security/limits.conf*: Replace <my_group> with a group to which your user belongs. Settings will not take effect until the user has logged in and out. +------------------------------------------------------------------------ +Misc notes +------------------------------------------------------------------------ + ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Support for dynamically loadable modules ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ |