soc/rtc: Bypass touchpad current to external 32k crystal oscillator

diff --git a/components/soc/esp32/rtc_clk.c b/components/soc/esp32/rtc_clk.c
index 8c2948553d76bfb56901b50c3ad41e69ef4fa28e..dfe332fa1303d7df3df0402928680fa9c4def7a0 100644 (file)
--- a/components/soc/esp32/rtc_clk.c
+++ b/components/soc/esp32/rtc_clk.c
@@ -58,7 +58,7 @@
 #define APLL_CAL_DELAY_2            0x3f
 #define APLL_CAL_DELAY_3            0x1f
 
-#define XTAL_32K_DAC_VAL    1
+#define XTAL_32K_DAC_VAL    3
 #define XTAL_32K_DRES_VAL   3
 #define XTAL_32K_DBIAS_VAL  0
 
@@ -111,14 +111,34 @@ static const char* TAG = "rtc_clk";
 
 static void rtc_clk_32k_enable_common(int dac, int dres, int dbias)
 {
-    SET_PERI_REG_MASK(RTC_IO_XTAL_32K_PAD_REG, RTC_IO_X32N_MUX_SEL | RTC_IO_X32P_MUX_SEL);
     CLEAR_PERI_REG_MASK(RTC_IO_XTAL_32K_PAD_REG,
-            RTC_IO_X32P_RDE | RTC_IO_X32P_RUE | RTC_IO_X32N_RUE |
-            RTC_IO_X32N_RDE | RTC_IO_X32N_MUX_SEL | RTC_IO_X32P_MUX_SEL);
+                        RTC_IO_X32P_RDE | RTC_IO_X32P_RUE | RTC_IO_X32N_RUE |
+                        RTC_IO_X32N_RDE | RTC_IO_X32N_MUX_SEL | RTC_IO_X32P_MUX_SEL);
+    SET_PERI_REG_MASK(RTC_IO_XTAL_32K_PAD_REG, RTC_IO_X32N_MUX_SEL | RTC_IO_X32P_MUX_SEL);
+    /* Set the parameters of xtal
+        dac --> current
+        dres --> resistance
+        dbias --> bais voltage
+    */
     REG_SET_FIELD(RTC_IO_XTAL_32K_PAD_REG, RTC_IO_DAC_XTAL_32K, dac);
     REG_SET_FIELD(RTC_IO_XTAL_32K_PAD_REG, RTC_IO_DRES_XTAL_32K, dres);
     REG_SET_FIELD(RTC_IO_XTAL_32K_PAD_REG, RTC_IO_DBIAS_XTAL_32K, dbias);
-    SET_PERI_REG_MASK(RTC_IO_XTAL_32K_PAD_REG, RTC_IO_XPD_XTAL_32K);
+
+    /* TOUCH sensor can provide additional current to external XTAL. 
+       In some case, X32N and X32P PAD don't have enough drive capability to start XTAL */
+    SET_PERI_REG_MASK(RTC_IO_TOUCH_CFG_REG, RTC_IO_TOUCH_XPD_BIAS_M);
+    /* Tie PAD Touch8 to VDD
+       NOTE: TOUCH8 and TOUCH9 register settings are reversed except for DAC, so we set RTC_IO_TOUCH_PAD9_REG here instead
+    */
+    SET_PERI_REG_MASK(RTC_IO_TOUCH_PAD9_REG, RTC_IO_TOUCH_PAD9_TIE_OPT_M);
+    /* Set the current used to compensate TOUCH PAD8 */
+    SET_PERI_REG_BITS(RTC_IO_TOUCH_PAD8_REG, RTC_IO_TOUCH_PAD8_DAC, 4, RTC_IO_TOUCH_PAD8_DAC_S);
+    /* Power up TOUCH8
+       So the Touch DAC start to drive some current from VDD to TOUCH8(which is also XTAL-N)
+     */
+    SET_PERI_REG_MASK(RTC_IO_TOUCH_PAD9_REG, RTC_IO_TOUCH_PAD9_XPD_M);
+    /* Power up external xtal */
+    SET_PERI_REG_MASK(RTC_IO_XTAL_32K_PAD_REG, RTC_IO_XPD_XTAL_32K_M);
 }
 
 void rtc_clk_32k_enable(bool enable)
@@ -126,7 +146,10 @@ void rtc_clk_32k_enable(bool enable)
     if (enable) {
         rtc_clk_32k_enable_common(XTAL_32K_DAC_VAL, XTAL_32K_DRES_VAL, XTAL_32K_DBIAS_VAL);
     } else {
+        /* Disable X32N and X32P pad drive external xtal */
         CLEAR_PERI_REG_MASK(RTC_IO_XTAL_32K_PAD_REG, RTC_IO_XPD_XTAL_32K);
+        /* Power down TOUCH */
+        CLEAR_PERI_REG_MASK(RTC_IO_TOUCH_PAD9_REG, RTC_IO_TOUCH_PAD9_XPD_M);
     }
 }