add a small document describing the use of the control interface

doc/control_interface.txt

@@ -0,0 +1,57 @@
+The osmo-bts control interface is currently supporting the following operations:
+
+h2. generic
+
+h3. trx.0.thermal-attenuation
+
+The idea of this paramter is to attenuate the system output power as part of
+thermal management.  In some cases the PA might be passing a critical level,
+so an external control process can use this attribute to reduce the system
+output power.
+
+<pre>
+bsc_control.py -d localhost -p 4238 -s trx.0.thermal-attenuation 3
+Got message: SET_REPLY 1 trx.0.thermal-attenuation 3
+</pre>
+
+<pre>
+bsc_control.py -d localhost -p 4238 -g trx.0.thermal-attenuation
+Got message: GET_REPLY 1 trx.0.thermal-attenuation 3
+</pre>
+
+
+h2. sysmobts specific
+
+h3. trx.0.clock-info
+
+obtain information on the current clock status:
+
+<pre>
+bsc_control.py -d localhost -p 4238 -g trx.0.clock-info
+Got message: GET_REPLY 1 trx.0.clock-info -100,ocxo,0,0,gps
+</pre>
+
+which is to be interpreted as:
+* current clock correction value is -100 ppb
+* current clock source is OCXO
+* deviation between clock source and calibration source is 0 ppb
+* resolution of clock error measurement is 0 ppt (0 means no result yet)
+* current calibration source is GPS
+
+When this attribute is set, any value passed on is discarded, but the clock
+calibration process is re-started.
+
+
+h3. trx.0.clock-correction
+
+This attribute can get and set the current clock correction value:
+
+<pre>
+bsc_control.py -d localhost -p 4238 -g trx.0.clock-correction
+Got message: GET_REPLY 1 trx.0.clock-correction -100
+</pre>
+
+<pre>
+bsc_control.py -d localhost -p 4238 -s trx.0.clock-correction -- -99
+Got message: SET_REPLY 1 trx.0.clock-correction success
+</pre>