sntp: Add API to set update interval

Closes: https://github.com/espressif/esp-idf/issues/4437
Closes: IDFGH-2298

components/lwip/apps/sntp/sntp.c

@@ -18,12 +18,14 @@
 #include <sys/time.h>
 #include "esp_log.h"
 #include "sntp.h"
+#include "lwip/apps/sntp.h"
 
 static const char *TAG = "sntp";
 
 static volatile sntp_sync_mode_t sntp_sync_mode = SNTP_SYNC_MODE_IMMED;
 static volatile sntp_sync_status_t sntp_sync_status = SNTP_SYNC_STATUS_RESET;
 static sntp_sync_time_cb_t time_sync_notification_cb = NULL;
+static uint32_t s_sync_interval = CONFIG_LWIP_SNTP_UPDATE_DELAY;
 
 inline void sntp_set_sync_status(sntp_sync_status_t sync_status)
 {
@@ -91,3 +93,27 @@ sntp_sync_status_t sntp_get_sync_status(void)
     }
     return ret_sync_status;
 }
+
+void sntp_set_sync_interval(uint32_t interval_ms)
+{
+    if (interval_ms < 15000) {
+        // SNTPv4 RFC 4330 enforces a minimum update time of 15 seconds
+        interval_ms = 15000;
+    }
+    s_sync_interval = interval_ms;
+}
+
+uint32_t sntp_get_sync_interval(void)
+{
+    return s_sync_interval;
+}
+
+bool sntp_restart(void)
+{
+    if (sntp_enabled()) {
+        sntp_stop();
+        sntp_init();
+        return true;
+    }
+    return false;
+}

components/lwip/include/apps/sntp/sntp.h

@@ -120,6 +120,33 @@ void sntp_set_sync_status(sntp_sync_status_t sync_status);
  */
 void sntp_set_time_sync_notification_cb(sntp_sync_time_cb_t callback);
 
+/**
+ * @brief Set the sync interval of SNTP operation
+ *
+ * Note: SNTPv4 RFC 4330 enforces a minimum sync interval of 15 seconds.
+ * This sync interval will be used in the next attempt update time throught SNTP.
+ * To apply the new sync interval call the sntp_restart() function,
+ * otherwise, it will be applied after the last interval expired.
+ *
+ * @param interval_ms   The sync interval in ms. It cannot be lower than 15 seconds, otherwise 15 seconds will be set.
+ */
+void sntp_set_sync_interval(uint32_t interval_ms);
+
+/**
+ * @brief Get the sync interval of SNTP operation
+ *
+ * @return  the sync interval
+ */
+uint32_t sntp_get_sync_interval(void);
+
+/**
+ * @brief Restart SNTP
+ *
+ * @return True  - Restart
+ *         False - SNTP was not initialized yet
+ */
+bool sntp_restart(void);
+
 #ifdef __cplusplus
 }
 #endif

components/lwip/port/esp32/include/lwipopts.h

@@ -844,7 +844,10 @@
  */
 #define SNTP_SERVER_DNS            1
 
-#define SNTP_UPDATE_DELAY              CONFIG_LWIP_SNTP_UPDATE_DELAY
+// It disables a check of SNTP_UPDATE_DELAY it is done in sntp_set_sync_interval
+#define SNTP_SUPPRESS_DELAY_CHECK
+
+#define SNTP_UPDATE_DELAY              (sntp_get_sync_interval())
 
 #define SNTP_SET_SYSTEM_TIME_US(sec, us)  \
     do { \