Merge branch 'bugfix/fix_xtal32k_error_detect' into 'master'

esp_hw_support/clk_cali: fix xtal32k error detect

Closes BT-2621 and IDF-5788

See merge request espressif/esp-idf!19500

components/esp_hw_support/port/esp32/rtc_time.c

@@ -115,10 +115,22 @@ uint32_t rtc_clk_cal_ratio(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
     return ratio;
 }
 
+static inline bool rtc_clk_cal_32k_valid(rtc_xtal_freq_t xtal_freq, uint32_t slowclk_cycles, uint64_t actual_xtal_cycles)
+{
+    uint64_t expected_xtal_cycles = (xtal_freq * 1000000ULL * slowclk_cycles) >> 15; // xtal_freq(hz) * slowclk_cycles / 32768
+    uint64_t delta = expected_xtal_cycles / 2000;                                    // 5/10000
+    return (actual_xtal_cycles >= (expected_xtal_cycles - delta)) && (actual_xtal_cycles <= (expected_xtal_cycles + delta));
+}
+
 uint32_t rtc_clk_cal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
 {
     rtc_xtal_freq_t xtal_freq = rtc_clk_xtal_freq_get();
     uint64_t xtal_cycles = rtc_clk_cal_internal(cal_clk, slowclk_cycles);
+
+    if ((cal_clk == RTC_CAL_32K_XTAL) && !rtc_clk_cal_32k_valid(xtal_freq, slowclk_cycles, xtal_cycles)) {
+        return 0;
+    }
+
     uint64_t divider = ((uint64_t)xtal_freq) * slowclk_cycles;
     uint64_t period_64 = ((xtal_cycles << RTC_CLK_CAL_FRACT) + divider / 2 - 1) / divider;
     uint32_t period = (uint32_t)(period_64 & UINT32_MAX);

components/esp_hw_support/port/esp32c2/rtc_init.c

@@ -165,7 +165,7 @@ static void calibrate_ocode(void)
     soc_rtc_slow_clk_src_t slow_clk_src = rtc_clk_slow_src_get();
     rtc_cal_sel_t cal_clk = RTC_CAL_RTC_MUX;
     if (slow_clk_src == SOC_RTC_SLOW_CLK_SRC_OSC_SLOW) {
-        cal_clk = RTC_CAL_EXT_CLK;
+        cal_clk = RTC_CAL_EXT_32K;
     } else if (slow_clk_src == SOC_RTC_SLOW_CLK_SRC_RC_FAST_D256) {
         cal_clk  = RTC_CAL_8MD256;
     }

components/esp_hw_support/port/esp32c2/rtc_time.c

@@ -40,14 +40,14 @@ uint32_t rtc_clk_cal_internal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
     if (cal_clk == RTC_CAL_RTC_MUX) {
         soc_rtc_slow_clk_src_t slow_clk_src = rtc_clk_slow_src_get();
         if (slow_clk_src == SOC_RTC_SLOW_CLK_SRC_OSC_SLOW) {
-            cal_clk = RTC_CAL_EXT_CLK;
+            cal_clk = RTC_CAL_EXT_32K;
         } else if (slow_clk_src == SOC_RTC_SLOW_CLK_SRC_RC_FAST_D256) {
             cal_clk = RTC_CAL_8MD256;
         }
     }
     /* Enable requested clock (150k clock is always on) */
     bool dig_ext_clk_enabled = clk_ll_xtal32k_digi_is_enabled();
-    if (cal_clk == RTC_CAL_EXT_CLK && !dig_ext_clk_enabled) {
+    if (cal_clk == RTC_CAL_EXT_32K && !dig_ext_clk_enabled) {
         clk_ll_xtal32k_digi_enable();
     }
 
@@ -78,7 +78,7 @@ uint32_t rtc_clk_cal_internal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
 
     /* Set timeout reg and expect time delay*/
     uint32_t expected_freq;
-    if (cal_clk == RTC_CAL_EXT_CLK) {
+    if (cal_clk == RTC_CAL_EXT_32K) {
         REG_SET_FIELD(TIMG_RTCCALICFG2_REG(0), TIMG_RTC_CALI_TIMEOUT_THRES, RTC_SLOW_CLK_X32K_CAL_TIMEOUT_THRES(slowclk_cycles));
         expected_freq = SOC_CLK_OSC_SLOW_FREQ_APPROX;
     } else if (cal_clk == RTC_CAL_8MD256) {
@@ -109,7 +109,7 @@ uint32_t rtc_clk_cal_internal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
     CLEAR_PERI_REG_MASK(TIMG_RTCCALICFG_REG(0), TIMG_RTC_CALI_START);
 
     /* if dig_ext_clk was originally off and enabled due to calibration, then set back to off state */
-    if (cal_clk == RTC_CAL_EXT_CLK && !dig_ext_clk_enabled) {
+    if (cal_clk == RTC_CAL_EXT_32K && !dig_ext_clk_enabled) {
         clk_ll_xtal32k_digi_disable();
     }
 
@@ -129,10 +129,22 @@ uint32_t rtc_clk_cal_ratio(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
     return ratio;
 }
 
+static inline bool rtc_clk_cal_32k_valid(rtc_xtal_freq_t xtal_freq, uint32_t slowclk_cycles, uint64_t actual_xtal_cycles)
+{
+    uint64_t expected_xtal_cycles = (xtal_freq * 1000000ULL * slowclk_cycles) >> 15; // xtal_freq(hz) * slowclk_cycles / 32768
+    uint64_t delta = expected_xtal_cycles / 2000;                                    // 5/10000
+    return (actual_xtal_cycles >= (expected_xtal_cycles - delta)) && (actual_xtal_cycles <= (expected_xtal_cycles + delta));
+}
+
 uint32_t rtc_clk_cal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
 {
     rtc_xtal_freq_t xtal_freq = rtc_clk_xtal_freq_get();
     uint64_t xtal_cycles = rtc_clk_cal_internal(cal_clk, slowclk_cycles);
+
+    if ((cal_clk == RTC_CAL_EXT_32K) && !rtc_clk_cal_32k_valid(xtal_freq, slowclk_cycles, xtal_cycles)) {
+        return 0;
+    }
+
     uint64_t divider = ((uint64_t)xtal_freq) * slowclk_cycles;
     uint64_t period_64 = ((xtal_cycles << RTC_CLK_CAL_FRACT) + divider / 2 - 1) / divider;
     uint32_t period = (uint32_t)(period_64 & UINT32_MAX);

components/esp_hw_support/port/esp32c3/rtc_time.c

@@ -133,10 +133,21 @@ uint32_t rtc_clk_cal_ratio(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
     return ratio;
 }
 
+static bool rtc_clk_cal_32k_valid(rtc_xtal_freq_t xtal_freq, uint32_t slowclk_cycles, uint64_t actual_xtal_cycles)
+{
+    uint64_t expected_xtal_cycles = (xtal_freq * 1000000ULL * slowclk_cycles) >> 15; // xtal_freq(hz) * slowclk_cycles / 32768
+    uint64_t delta = expected_xtal_cycles / 2000;                                    // 5/10000
+    return (actual_xtal_cycles >= (expected_xtal_cycles - delta)) && (actual_xtal_cycles <= (expected_xtal_cycles + delta));
+}
+
 uint32_t rtc_clk_cal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
 {
     rtc_xtal_freq_t xtal_freq = rtc_clk_xtal_freq_get();
     uint64_t xtal_cycles = rtc_clk_cal_internal(cal_clk, slowclk_cycles);
+
+    if ((cal_clk == RTC_CAL_32K_XTAL) && !rtc_clk_cal_32k_valid(xtal_freq, slowclk_cycles, xtal_cycles))
+        return 0;
+
     uint64_t divider = ((uint64_t)xtal_freq) * slowclk_cycles;
     uint64_t period_64 = ((xtal_cycles << RTC_CLK_CAL_FRACT) + divider / 2 - 1) / divider;
     uint32_t period = (uint32_t)(period_64 & UINT32_MAX);

components/esp_hw_support/port/esp32h2/rtc_time.c

@@ -126,10 +126,22 @@ uint32_t rtc_clk_cal_ratio(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
     return ratio;
 }
 
+static inline bool rtc_clk_cal_32k_valid(rtc_xtal_freq_t xtal_freq, uint32_t slowclk_cycles, uint64_t actual_xtal_cycles)
+{
+    uint64_t expected_xtal_cycles = (xtal_freq * 1000000ULL * slowclk_cycles) >> 15; // xtal_freq(hz) * slowclk_cycles / 32768
+    uint64_t delta = expected_xtal_cycles / 2000;                                    // 5/10000
+    return (actual_xtal_cycles >= (expected_xtal_cycles - delta)) && (actual_xtal_cycles <= (expected_xtal_cycles + delta));
+}
+
 uint32_t rtc_clk_cal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
 {
     rtc_xtal_freq_t xtal_freq = rtc_clk_xtal_freq_get();
     uint64_t xtal_cycles = rtc_clk_cal_internal(cal_clk, slowclk_cycles);
+
+    if ((cal_clk == RTC_CAL_32K_XTAL) && !rtc_clk_cal_32k_valid(xtal_freq, slowclk_cycles, xtal_cycles)) {
+        return 0;
+    }
+
     uint64_t divider = ((uint64_t)xtal_freq) * slowclk_cycles;
     uint64_t period_64 = ((xtal_cycles << RTC_CLK_CAL_FRACT) + divider / 2 - 1) / divider;
     uint32_t period = (uint32_t)(period_64 & UINT32_MAX);

components/esp_hw_support/port/esp32s2/rtc_time.c

@@ -194,11 +194,22 @@ uint32_t rtc_clk_cal_ratio(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
     return ratio;
 }
 
+static inline bool rtc_clk_cal_32k_valid(rtc_xtal_freq_t xtal_freq, uint32_t slowclk_cycles, uint64_t actual_xtal_cycles)
+{
+    uint64_t expected_xtal_cycles = (xtal_freq * 1000000ULL * slowclk_cycles) >> 15; // xtal_freq(hz) * slowclk_cycles / 32768
+    uint64_t delta = expected_xtal_cycles / 2000;                                    // 5/10000
+    return (actual_xtal_cycles >= (expected_xtal_cycles - delta)) && (actual_xtal_cycles <= (expected_xtal_cycles + delta));
+}
+
 uint32_t rtc_clk_cal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
 {
     uint64_t xtal_cycles = rtc_clk_cal_internal(cal_clk, slowclk_cycles, RTC_TIME_CAL_ONEOFF_MODE);
-    uint32_t period = rtc_clk_xtal_to_slowclk(xtal_cycles, slowclk_cycles);
-    return period;
+
+    if ((cal_clk == RTC_CAL_32K_XTAL) && !rtc_clk_cal_32k_valid(rtc_clk_xtal_freq_get(), slowclk_cycles, xtal_cycles)) {
+        return 0;
+    }
+
+    return rtc_clk_xtal_to_slowclk(xtal_cycles, slowclk_cycles);
 }
 
 uint32_t rtc_clk_cal_cycling(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)

components/esp_hw_support/port/esp32s3/rtc_time.c

@@ -131,10 +131,22 @@ uint32_t rtc_clk_cal_ratio(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
     return ratio;
 }
 
+static inline bool rtc_clk_cal_32k_valid(rtc_xtal_freq_t xtal_freq, uint32_t slowclk_cycles, uint64_t actual_xtal_cycles)
+{
+    uint64_t expected_xtal_cycles = (xtal_freq * 1000000ULL * slowclk_cycles) >> 15; // xtal_freq(hz) * slowclk_cycles / 32768
+    uint64_t delta = expected_xtal_cycles / 2000;                                    // 5/10000
+    return (actual_xtal_cycles >= (expected_xtal_cycles - delta)) && (actual_xtal_cycles <= (expected_xtal_cycles + delta));
+}
+
 uint32_t rtc_clk_cal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles)
 {
     rtc_xtal_freq_t xtal_freq = rtc_clk_xtal_freq_get();
     uint64_t xtal_cycles = rtc_clk_cal_internal(cal_clk, slowclk_cycles);
+
+    if ((cal_clk == RTC_CAL_32K_XTAL) && !rtc_clk_cal_32k_valid(xtal_freq, slowclk_cycles, xtal_cycles)) {
+        return 0;
+    }
+
     uint64_t divider = ((uint64_t)xtal_freq) * slowclk_cycles;
     uint64_t period_64 = ((xtal_cycles << RTC_CLK_CAL_FRACT) + divider / 2 - 1) / divider;
     uint32_t period = (uint32_t)(period_64 & UINT32_MAX);

components/esp_hw_support/test/test_rtc_clk.c

@@ -83,7 +83,7 @@ TEST_CASE("RTC_SLOW_CLK sources calibration", "[rtc_clk]")
     CALIBRATE_ONE(RTC_CAL_8MD256);
 
 #if CONFIG_IDF_TARGET_ESP32C2
-    uint32_t cal_ext_slow_clk = CALIBRATE_ONE(RTC_CAL_EXT_CLK);
+    uint32_t cal_ext_slow_clk = CALIBRATE_ONE(RTC_CAL_EXT_32K);
     if (cal_ext_slow_clk == 0) {
         printf("EXT CLOCK by PIN has not started up");
     } else {
@@ -93,7 +93,7 @@ TEST_CASE("RTC_SLOW_CLK sources calibration", "[rtc_clk]")
 
         CALIBRATE_ONE(RTC_CAL_RTC_MUX);
         CALIBRATE_ONE(RTC_CAL_8MD256);
-        CALIBRATE_ONE(RTC_CAL_EXT_CLK);
+        CALIBRATE_ONE(RTC_CAL_EXT_32K);
     }
 #else
     uint32_t cal_32k = CALIBRATE_ONE(RTC_CAL_32K_XTAL);
@@ -116,7 +116,7 @@ TEST_CASE("RTC_SLOW_CLK sources calibration", "[rtc_clk]")
     CALIBRATE_ONE(RTC_CAL_RTC_MUX);
     CALIBRATE_ONE(RTC_CAL_8MD256);
 #if CONFIG_IDF_TARGET_ESP32C2
-    CALIBRATE_ONE(RTC_CAL_EXT_CLK);
+    CALIBRATE_ONE(RTC_CAL_EXT_32K);
 #else
     CALIBRATE_ONE(RTC_CAL_32K_XTAL);
 #endif

components/esp_system/port/soc/esp32/clk.c

@@ -36,11 +36,6 @@ static const char* TAG = "clk";
 #define RTC_XTAL_CAL_RETRY 1
 #endif
 
-/* Lower threshold for a reasonably-looking calibration value for a 32k XTAL.
- * The ideal value (assuming 32768 Hz frequency) is 1000000/32768*(2**19) = 16*10^6.
- */
-#define MIN_32K_XTAL_CAL_VAL  15000000L
-
 /* Indicates that this 32k oscillator gets input from external oscillator, rather
  * than a crystal.
  */
@@ -84,7 +79,7 @@ static void select_rtc_slow_clk(slow_clk_sel_t slow_clk)
             // 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_32K_XTAL, SLOW_CLK_CAL_CYCLES);
-                if (cal_val == 0 || cal_val < MIN_32K_XTAL_CAL_VAL) {
+                if (cal_val == 0) {
                     if (retry_32k_xtal-- > 0) {
                         continue;
                     }

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

@@ -35,11 +35,6 @@
 
 #define MHZ (1000000)
 
-/* Lower threshold for a reasonably-looking calibration value for a 32k XTAL.
- * The ideal value (assuming 32768 Hz frequency) is 1000000/32768*(2**19) = 16*10^6.
- */
-#define MIN_32K_XTAL_CAL_VAL  15000000L
-
 /* Indicates that this 32k oscillator gets input from external oscillator, rather
  * than a crystal.
  */
@@ -154,8 +149,8 @@ static void select_rtc_slow_clk(slow_clk_sel_t slow_clk)
 
             // 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);
-                if (cal_val == 0 || cal_val < MIN_32K_XTAL_CAL_VAL) {
+                cal_val = rtc_clk_cal(RTC_CAL_EXT_32K, SLOW_CLK_CAL_CYCLES);
+                if (cal_val == 0) {
                     if (retry_ext_clk-- > 0) {
                         continue;
                     }

components/esp_system/port/soc/esp32c3/clk.c

@@ -36,11 +36,6 @@
 
 #define MHZ (1000000)
 
-/* Lower threshold for a reasonably-looking calibration value for a 32k XTAL.
- * The ideal value (assuming 32768 Hz frequency) is 1000000/32768*(2**19) = 16*10^6.
- */
-#define MIN_32K_XTAL_CAL_VAL  15000000L
-
 /* Indicates that this 32k oscillator gets input from external oscillator, rather
  * than a crystal.
  */
@@ -165,7 +160,7 @@ static void select_rtc_slow_clk(slow_clk_sel_t slow_clk)
             // 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_32K_XTAL, SLOW_CLK_CAL_CYCLES);
-                if (cal_val == 0 || cal_val < MIN_32K_XTAL_CAL_VAL) {
+                if (cal_val == 0) {
                     if (retry_32k_xtal-- > 0) {
                         continue;
                     }

components/esp_system/port/soc/esp32h2/clk.c

@@ -36,11 +36,6 @@
 
 #define MHZ (1000000)
 
-/* Lower threshold for a reasonably-looking calibration value for a 32k XTAL.
- * The ideal value (assuming 32768 Hz frequency) is 1000000/32768*(2**19) = 16*10^6.
- */
-#define MIN_32K_XTAL_CAL_VAL  15000000L
-
 /* Indicates that this 32k oscillator gets input from external oscillator, rather
  * than a crystal.
  */
@@ -157,7 +152,7 @@ static void select_rtc_slow_clk(slow_clk_sel_t slow_clk)
             // 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_32K_XTAL, SLOW_CLK_CAL_CYCLES);
-                if (cal_val == 0 || cal_val < MIN_32K_XTAL_CAL_VAL) {
+                if (cal_val == 0) {
                     if (retry_32k_xtal-- > 0) {
                         continue;
                     }

components/esp_system/port/soc/esp32s2/clk.c

@@ -42,11 +42,6 @@ static const char *TAG = "clk";
 #define RTC_XTAL_CAL_RETRY 1
 #endif
 
-/* Lower threshold for a reasonably-looking calibration value for a 32k XTAL.
- * The ideal value (assuming 32768 Hz frequency) is 1000000/32768*(2**19) = 16*10^6.
- */
-#define MIN_32K_XTAL_CAL_VAL  15000000L
-
 /* Indicates that this 32k oscillator gets input from external oscillator, rather
  * than a crystal.
  */
@@ -170,7 +165,7 @@ static void select_rtc_slow_clk(slow_clk_sel_t slow_clk)
             // 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_32K_XTAL, SLOW_CLK_CAL_CYCLES);
-                if (cal_val == 0 || cal_val < MIN_32K_XTAL_CAL_VAL) {
+                if (cal_val == 0) {
                     if (retry_32k_xtal-- > 0) {
                         continue;
                     }

components/esp_system/port/soc/esp32s3/clk.c

@@ -36,11 +36,6 @@ static const char *TAG = "clk";
 
 #define RTC_XTAL_CAL_RETRY 1
 
-/* Lower threshold for a reasonably-looking calibration value for a 32k XTAL.
- * The ideal value (assuming 32768 Hz frequency) is 1000000/32768*(2**19) = 16*10^6.
- */
-#define MIN_32K_XTAL_CAL_VAL  15000000L
-
 /* Indicates that this 32k oscillator gets input from external oscillator, rather
  * than a crystal.
  */
@@ -159,7 +154,7 @@ static void select_rtc_slow_clk(slow_clk_sel_t slow_clk)
             // 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_32K_XTAL, SLOW_CLK_CAL_CYCLES);
-                if (cal_val == 0 || cal_val < MIN_32K_XTAL_CAL_VAL) {
+                if (cal_val == 0) {
                     if (retry_32k_xtal-- > 0) {
                         continue;
                     }

components/soc/esp32/include/soc/rtc.h

@@ -394,6 +394,11 @@ uint32_t rtc_clk_apb_freq_get(void);
  * 32k XTAL is being calibrated, but the oscillator has not started up (due to
  * incorrect loading capacitance, board design issue, or lack of 32 XTAL on board).
  *
+ * @note When 32k CLK is being calibrated, this function will check the accuracy
+ * of the clock. Since the xtal 32k or ext osc 32k is generally very stable, if
+ * the check fails, then consider this an invalid 32k clock and return 0. This
+ * check can filter some jamming signal.
+ *
  * @param cal_clk  clock to be measured
  * @param slow_clk_cycles  number of slow clock cycles to average
  * @return average slow clock period in microseconds, Q13.19 fixed point format,

components/soc/esp32c2/include/soc/clk_tree_defs.h

@@ -51,7 +51,7 @@ typedef enum {
     SOC_ROOT_CLK_INT_RC_FAST,          /*!< Internal 17.5MHz RC oscillator */
     SOC_ROOT_CLK_INT_RC_SLOW,          /*!< Internal 136kHz RC oscillator */
     SOC_ROOT_CLK_EXT_XTAL,             /*!< External 26/40MHz crystal */
-    SOC_ROOT_CLK_EXT_OSC_SLOW,         /*!< External slow clock signal at pin0 */
+    SOC_ROOT_CLK_EXT_OSC_SLOW,         /*!< External slow clock signal at pin0, only support 32.768 KHz currently */
 } soc_root_clk_t;
 
 /**

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

@@ -153,7 +153,7 @@ typedef struct rtc_cpu_freq_config_s {
 typedef enum {
     RTC_CAL_RTC_MUX = 0,       //!< Currently selected RTC SLOW_CLK
     RTC_CAL_8MD256 = 1,        //!< Internal 8 MHz RC oscillator, divided by 256
-    RTC_CAL_EXT_CLK = 2        //!< External CLK
+    RTC_CAL_EXT_32K = 2        //!< External 32.768 KHz CLK
 } rtc_cal_sel_t;
 
 /**
@@ -403,6 +403,11 @@ uint32_t rtc_clk_cal_internal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles);
  * 32k XTAL is being calibrated, but the oscillator has not started up (due to
  * incorrect loading capacitance, board design issue, or lack of 32 XTAL on board).
  *
+ * @note When 32k CLK is being calibrated, this function will check the accuracy
+ * of the clock. Since the xtal 32k or ext osc 32k is generally very stable, if
+ * the check fails, then consider this an invalid 32k clock and return 0. This
+ * check can filter some jamming signal.
+ *
  * @param cal_clk  clock to be measured
  * @param slow_clk_cycles  number of slow clock cycles to average
  * @return average slow clock period in microseconds, Q13.19 fixed point format,

components/soc/esp32c3/include/soc/rtc.h

@@ -430,6 +430,11 @@ uint32_t rtc_clk_cal_internal(rtc_cal_sel_t cal_clk, uint32_t slowclk_cycles);
  * 32k XTAL is being calibrated, but the oscillator has not started up (due to
  * incorrect loading capacitance, board design issue, or lack of 32 XTAL on board).
  *
+ * @note When 32k CLK is being calibrated, this function will check the accuracy
+ * of the clock. Since the xtal 32k or ext osc 32k is generally very stable, if
+ * the check fails, then consider this an invalid 32k clock and return 0. This
+ * check can filter some jamming signal.
+ *
  * @param cal_clk  clock to be measured
  * @param slow_clk_cycles  number of slow clock cycles to average
  * @return average slow clock period in microseconds, Q13.19 fixed point format,