The Test System Interface Daemon (TSID) will provide a connection-oriented
(SOCK_STREAM) UNIX domain local socket at /tmp/fc_rftest_socket, and will speak
an ASCII line-based command-response protocol on this socket.  All command and
response lines will end with \n only (no \r), and each TSID response including
the initial greeting on connection establishment will begin with a '+' or '-'
character to indicate OK or error, respectively, like in POP3.

The following commands are currently defined:

vcxo-cal-setup band arfcn

This command is sent to the TSID to prepare the RF test system for the VCXO
calibration procedure.  The first argument after the command keyword is the
band to be used (850, 900, 1800 or 1900) and the second argument is the ARFCN
in that band on which the DUT will be transmitting.

freq-meas hint

This command directs the RF test system to take a frequency offset measurement
(vcxo-cal-setup must have been performed previously) and report it back to the
client in the response line.  The hint argument after the freq-meas keyword will
be sent by the VCXO calibration program (fc-rfcal-vcxo) to tell the RF test
system what kind of frequency offset measurement is being made, i.e., which step
in the VCXO calibration sequence is being performed; the hint keywords remain
to be defined.

signal-gen-setup band

This command is sent to the TSID to prepare the RF test system for tests in
which the latter acts as a signal generator.  The argument after the command
keyword is the band number (850, 900, 1800 or 1900), and it selects the
downlink frequency band in which the signal generator will need to operate.

signal-gen-sine arfcn offset level

This command directs the RF test system to turn on its signal generator and put
out a pure sine wave at the frequency corresponding to the specified ARFCN (in
the downlink band previously selected with signal-get-setup) plus the specified
offset in kHz (-67 or +67 with TI's Rx path calibration procedures), and at the
specified Tx power level in dBm.

signal-gen-off

Turn off the signal generator.

The commands for Tx power level calibration remain to be defined.