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 transmitter runs on a single thread and supports rates up to 192 kHz.

The S/PDIF transmitter thread takes PCM audio samples via a channel and outputs them in S/PDIF format to a port. Samples are provided to the S/PDIF transmitter task from the XUA_AudioHub() task.

The channel should be declared as normal:

chan c_spdif_tx

In order to use the S/PDIF transmitter with lib_xua a 1-bit port must be declared e.g:

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_tx, 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 statement.

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_tx, c_spdif_tx);
    }

    /* AudioHub/IO thread 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.