Remote control protocol.

Supported commands:
 f
    Get frequency [Hz]
 F <frequency>
    Set frequency [Hz]
 m
    Get demodulator mode and passband
 M <mode> [passband]
    Set demodulator mode and passband [Hz]
    Passing a '?' as the first argument instead of 'mode' will return
    a space separated list of radio backend supported modes.
 l STRENGTH
    Get signal strength [dBFS]
 l SQL
    Get squelch threshold [dBFS]
 L SQL <sql>
    Set squelch threshold to <sql> [dBFS]
 u RECORD
    Get status of audio recorder
 U RECORD <status>
    Set status of audio recorder to <status>
 q|Q
    Close connection
 AOS
    Acquisition of signal (AOS) event, start audio recording
 LOS
    Loss of signal (LOS) event, stop audio recording
 LNB_LO [frequency]
    If frequency [Hz] is specified set the LNB LO frequency used for
    display. Otherwise print the current LNB LO frequency [Hz].
 \dump_state
    Dump state (only usable for hamlib compatibility)
 v
    Get 'VFO' (only usable for hamlib compatibility)
 V
    Set 'VFO' (only usable for hamlib compatibility)
 s
    Get 'Split' mode (only usable for hamlib compatibility)
 S
    Set 'Split' mode (only usable for hamlib compatibility)
 _
    Get version


Reply:
 RPRT 0
    Command successful
 RPRT 1
    Command failed