am335x mcasp as the i2s master and codec as the slave

dear all

Now I want to port a new codec driver  tas5716 to am335x ics platform .

As the tas5716 can only as the slave ,i change the am335x mcasp as the maser .

#define AUDIO_FORMAT (SND_SOC_DAIFMT_DSP_B | \
                SND_SOC_DAIFMT_CBM_CFM | SND_SOC_DAIFMT_IB_NF)

to 

#define AUDIO_FORMAT (SND_SOC_DAIFMT_DSP_B | \
                SND_SOC_DAIFMT_CBS_CFS | SND_SOC_DAIFMT_IB_NF)

now the i2s BCLK(mcasp_aclkx) alwalys is 24mhz,the WCLK(mcasp_fsx) is 750khz,

the codec can  not work,have no audo.

Anybody know how to change to BCLK(mcasp_aclkx)?