SPDIF tx doc update

lib_xua/doc/rst/feat.rst

@@ -63,10 +63,12 @@ S/PDIF Transmit
 ~~~~~~~~~~~~~~~
 
 ``lib_xua`` supports the development of devices with S/PDIF transmit functionality through the use of 
-``lib_spdif``. The XMOS S/PDIF transmitted runs in a single core and supports rates up to 192kHz.
+``lib_spdif``. The XMOS S/PDIF transmitter runs in a single core and supports rates up to 192kHz.
 
 The S/PDIF transmitter core takes PCM audio samples via a channel and outputs them
-in S/PDIF format to a port. 
+in S/PDIF format to a port. The channel should be declared a normal::
+
+    chan c_spdif_tx
 
 Samples are provided to the S/PDIF transmitter task from the ``XUA_AudioHub()`` task.
 
@@ -74,6 +76,28 @@ In order to use the S/PDIF transmmiter with ``lib_xua`` hardware resources must
 
     buffered out port:32 p_spdif_tx         = PORT_SPDIF_OUT;     /* SPDIF transmit port */
 
+This port should be clocked from the master-clock, ``lib_spdif`` provides a helper function for setting up the port::
+
+    spdif_tx_port_config(p_spdif_tx2, clk_audio_mclk, p_mclk_in, delay);
+
+.. note:: If sharing the master-clock port and clockblock with ``XUA_AudioHub()`` (or any other task) then this setup
+          should be done before running the tasks in a par{}
+
+Finally the S/PDIF transmitter task must be run - passing in the port and channel for communication with ``XUA_AudioHub``.
+For example::
+
+    par
+    {
+        while(1)
+        {
+            /* Run the S/PDIF transmitter task */
+            spdif_tx(p_spdif_tx2, c_spdif_tx);   
+        }
+    
+        /* AudioHub/IO core does most of the audio IO i.e. I2S (also serves as a hub for all audio) */
+        /* Note, since we are not using I2S we pass in null for LR and Bit clock ports and the I2S dataline ports */
+        XUA_AudioHub(c_aud, clk_audio_mclk, null, p_mclk_in, null, null, null, null, c_spdif_tx);
+    }
 
 For further details please see the documentation, application notes and examples provided for ``lib_spdif``.