Enable Sidetone Feature on DA7218 Audio Codec

I'm trying to enable the sidetone feature for the DA7218 audio codec. Both microphone and speaker work fine. However the sidetone doesn't work.

I'm using the DA14195DEVKTD with SDK v.1.6.2.

# include <组件\司机\ Codec\Include\DA7217\IDrvCodec_DA7217.h> #include  static void EnableSidetone(void) { uint16_t reg; writeCodecReg(SIDETONE_IN_SELECT_REG_adr, SIDE_TONE_SELCET_ADC_2L); // Use anlog mic on ADC2 as a source reg = readCodecReg(DROUTING_ST_OUTFILT_1L_REG_adr); // Enable sidetone for left channel reg |= (1 << 2); writeCodecReg(DROUTING_ST_OUTFILT_1L_REG_adr, reg); reg = readCodecReg(DROUTING_ST_OUTFILT_1R_REG_adr); // Enabled sidetone for right channel reg |= (1 << 2); writeCodecReg(DROUTING_ST_OUTFILT_1R_REG_adr, reg); writeCodecReg(SIDETONE_GAIN_REG_adr, 0x1c); // Set sidetone gain to 0 dB reg = SIDETONE_CTRL_SIDETONE_FILTER_EN; writeCodecReg(SIDETONE_CTRL_REG_adr, reg); // sidetone_filter_en=1, sidetone_mute_en=0 }

The coefficients of the sidetone biquad filter are left at the reset values.