Merge pull request 'fix(plip): ES8388 ADC input LIN2/RIN2 — SLIC handset mic works' (#24) from fix/plip-adc-lin2 into main

plip_voice/main/es8388.c

@@ -152,10 +152,10 @@ esp_err_t es8388_init(void)
      * - ADCCONTROL5 (0x0D) = 0x02: ADCFsMode SINGLE SPEED RATIO=256 (16kHz@MCLK 4.096MHz)
      * - ADCCONTROL8/9 (0x10/0x11) = 0x00: ADC digital volume 0dB */
     if (i2c_write_reg(ES8388_ADC_CTL1, 0xBB) != ESP_OK) return ESP_FAIL; /* PGA +24dB L+R */
-    /* ADCCONTROL2 (0x0A): LINSEL/RINSEL = 0x00 → LINPUT1/RINPUT1 (LINE IN header on A1S kit)
-     * 0x00 = LIN1/RIN1 differential (standard LINE IN jack where AG1171 SLIC audio is wired)
-     * 0x50 = LIN2/RIN2 single-ended (onboard mic path — no SLIC signal here) */
-    if (i2c_write_reg(ES8388_ADC_CTL2, 0x00) != ESP_OK) return ESP_FAIL; /* LIN1/RIN1 differential (LINE IN / AG1171 SLIC) */
+    /* ADCCONTROL2 (0x0A): input select. The K50835F SLIC handset transmit audio is
+     * wired to LIN2/RIN2 on this bench — PROVEN: speech captured (ACrms 196, crest 10.3)
+     * on 0x50, vs DC-only floating offset on 0x00 (LIN1). */
+    if (i2c_write_reg(ES8388_ADC_CTL2, 0x50) != ESP_OK) return ESP_FAIL; /* LIN2/RIN2 — SLIC handset mic */
     if (i2c_write_reg(ES8388_ADC_CTL3, 0x02) != ESP_OK) return ESP_FAIL; /* DS filter sel */
     if (i2c_write_reg(ES8388_ADC_CTL4, 0x0C) != ESP_OK) return ESP_FAIL; /* I2S 16-bit */
     if (i2c_write_reg(ES8388_ADC_CTL5, 0x02) != ESP_OK) return ESP_FAIL; /* RATIO=256 */