flush to sd card before sleep

src/reset.cpp

@@ -126,6 +126,11 @@ void enter_deepsleep(const uint64_t wakeup_sec, gpio_num_t wakeup_gpio) {
   sds011_sleep();
 #endif
 
+// flush & close sd card, if we have
+#if (HAS_SDCARD)
+  sdcard_close();
+#endif
+
   // wait a while (max 100 sec) to clear send queues
   ESP_LOGI(TAG, "Waiting until send queues are empty...");
   for (i = 100; i > 0; i--) {

src/sdcard.cpp

@@ -13,7 +13,13 @@ static void createFile(void);
 
 File fileSDCard;
 
-bool sdcard_init() {
+bool sdcard_close(void) {
+  ESP_LOGD(TAG, "unmounting SD-card");
+  fileSDCard.flush();
+  fileSDCard.end();
+}
+
+bool sdcard_init(bool create) {
   ESP_LOGI(TAG, "looking for SD-card...");
 
   // for usage of SD drivers on ESP32 platform see