Hi Zheng,
As for as my knowledge is concern, you can play the Audio in two ways of interface which are I2S and SAIF. The audio operation STGL5000 is depends CTRL_MODE pin. If CTRL_MODE = 0 then the Data's transferred using I2C and if CTRL_MODE = 1 then the Data's transferred using I2S. Please check the hardware configuration of IC. By default stereo audio codec is controlled by the I2C interface. The audio data is transferred from the user data
buffer to/from the SAIF FIFO through the DMA channel. Playback uses SAIF0 and Record uses SAIF1.
SAIF0 works in master mode and provides the MCLK, BCLK and LRCLK, SAIF1 and SGTL5000 codec
work in slave mode, using clock of SAIF0. The BCLK and LRCLK are configured according to the audio
sample rate.
This is just general information form my side.
Thank you,
RAM