enable external 32k osc for esp32c2

components/esp_hw_support/port/esp32c2/rtc_clk.c

@@ -19,6 +19,8 @@
 #include "soc/efuse_reg.h"
 #include "soc/syscon_reg.h"
 #include "soc/system_reg.h"
+#include "soc/io_mux_reg.h"
+#include "soc/soc.h"
 #include "regi2c_ctrl.h"
 #include "regi2c_bbpll.h"
 #include "esp_hw_log.h"
@@ -35,6 +37,12 @@ static int s_cur_pll_freq;
 
 static void rtc_clk_cpu_freq_to_8m(void);
 
+void rtc_clk_32k_enable_external(void)
+{
+    REG_SET_BIT(PERIPHS_IO_MUX_XTAL_32K_P_U, FUN_IE);
+    REG_SET_BIT(RTC_CNTL_PAD_HOLD_REG, RTC_CNTL_GPIO_PIN0_HOLD);
+}
+
 void rtc_clk_8m_enable(bool clk_8m_en, bool d256_en)
 {
     if (clk_8m_en) {

components/esp_system/port/soc/esp32c2/clk.c

@@ -147,6 +147,8 @@ static void select_rtc_slow_clk(slow_clk_sel_t slow_clk)
              * will time out, returning 0.
              */
             ESP_EARLY_LOGD(TAG, "waiting for external clock by pin0 to start up");
+            rtc_clk_32k_enable_external();
+
             // When SLOW_CLK_CAL_CYCLES is set to 0, clock calibration will not be performed at startup.
             if (SLOW_CLK_CAL_CYCLES > 0) {
                 cal_val = rtc_clk_cal(RTC_CAL_EXT_CLK, SLOW_CLK_CAL_CYCLES);

components/soc/esp32c2/include/soc/rtc.h

@@ -240,6 +240,11 @@ rtc_xtal_freq_t rtc_clk_xtal_freq_get(void);
  */
 void rtc_clk_xtal_freq_update(rtc_xtal_freq_t xtal_freq);
 
+/**
+ * @brief Enable 32KHz external oscillator
+ */
+void rtc_clk_32k_enable_external(void);
+
 /**
  * @brief Enable or disable 8 MHz internal oscillator
  *