diff --git a/src/utility/Power_Class.cpp b/src/utility/Power_Class.cpp
index 2189340..e929077 100644
--- a/src/utility/Power_Class.cpp
+++ b/src/utility/Power_Class.cpp
@@ -1264,6 +1264,12 @@ namespace m5
 
   void Power_Class::deepSleep(std::uint64_t micro_seconds, bool touch_wakeup)
   {
+    if (micro_seconds == 0)
+    { // A wakeup time of zero means "do not sleep".
+      // ( This check comes before the display is put to sleep. )
+      M5_LOGW("deepSleep: micro_seconds is 0. not sleeping. ( use Power.sleep_no_timer to sleep without a timer wakeup )");
+      return;
+    }
     M5.Display.sleep();
     M5.Display.waitDisplay();
 #if defined (M5UNIFIED_PC_BUILD)
@@ -1287,32 +1293,52 @@ namespace m5
     {
       wpin = GPIO_NUM_4;
     }
+    bool pin_wakeup_enabled = false;
     if (touch_wakeup && wpin < GPIO_NUM_MAX)
     {
 #if SOC_PM_SUPPORT_EXT0_WAKEUP
-      esp_sleep_enable_ext0_wakeup((gpio_num_t)wpin, false);
+      pin_wakeup_enabled = (ESP_OK == esp_sleep_enable_ext0_wakeup((gpio_num_t)wpin, false));
 #elif SOC_PM_SUPPORT_EXT1_WAKEUP && SOC_RTCIO_PIN_COUNT > 0
-      const uint64_t ext_wakeup_pin_1_mask = 1ULL << _wakeupPin;
-      ESP_ERROR_CHECK(esp_sleep_enable_ext1_wakeup_io(ext_wakeup_pin_1_mask, ESP_EXT1_WAKEUP_ANY_LOW));
+      if (rtc_gpio_is_valid_gpio((gpio_num_t)wpin))
+      {
+        const uint64_t ext_wakeup_pin_1_mask = 1ULL << wpin;
+        pin_wakeup_enabled = (ESP_OK == esp_sleep_enable_ext1_wakeup_io(ext_wakeup_pin_1_mask, ESP_EXT1_WAKEUP_ANY_LOW));
  #if SOC_RTCIO_INPUT_OUTPUT_SUPPORTED
-      ESP_ERROR_CHECK(rtc_gpio_pullup_dis((gpio_num_t)_wakeupPin));
-      ESP_ERROR_CHECK(rtc_gpio_pulldown_en((gpio_num_t)_wakeupPin));
+        if (pin_wakeup_enabled)
+        {
+          rtc_gpio_pullup_dis((gpio_num_t)wpin);
+          rtc_gpio_pulldown_en((gpio_num_t)wpin);
+        }
  #endif
+      }
 #endif
-      while (m5gfx::gpio_in(wpin) == false)
+      if (pin_wakeup_enabled)
       {
-        // Issue #91, ( M5Paper wakes too soon from deep sleep when touch wakeup is enabled - with solution )
-        M5.update();
-        m5gfx::delay(10);
+        while (m5gfx::gpio_in(wpin) == false)
+        {
+          // Issue #91, ( M5Paper wakes too soon from deep sleep when touch wakeup is enabled - with solution )
+          M5.update();
+          m5gfx::delay(10);
+        }
+      }
+      else
+      { // The wakeup pin is not an RTC IO. ( ex. M5PaperS3 touch INT = GPIO48 )
+        // Such a pin can wake up from light sleep, but not from deep sleep.
+        M5_LOGW("deepSleep: GPIO%d cannot be used as a deep sleep wakeup source.", (int)wpin);
       }
     }
-    if (micro_seconds > 0)
+    if (micro_seconds != sleep_no_timer)
     {
       esp_sleep_enable_timer_wakeup(micro_seconds);
     }
     else
     {
       esp_sleep_disable_wakeup_source(ESP_SLEEP_WAKEUP_TIMER);
+      if (!pin_wakeup_enabled)
+      { // Neither a timer nor a wakeup pin was configured by this call.
+        // Unless another wakeup source has been set up, the device will not wake up until it is reset.
+        M5_LOGW("deepSleep: no timer or pin wakeup source is enabled.");
+      }
     }
 #endif
     esp_deep_sleep_start();
@@ -1321,6 +1347,11 @@ namespace m5
 
   void Power_Class::lightSleep(std::uint64_t micro_seconds, bool touch_wakeup)
   {
+    if (micro_seconds == 0)
+    { // A wakeup time of zero means "do not sleep".
+      M5_LOGW("lightSleep: micro_seconds is 0. not sleeping. ( use Power.sleep_no_timer to sleep without a timer wakeup )");
+      return;
+    }
 #if defined (M5UNIFIED_PC_BUILD)
     (void)micro_seconds;
     (void)touch_wakeup;
@@ -1342,31 +1373,43 @@ namespace m5
     {
       wpin = GPIO_NUM_4;
     }
+    bool pin_wakeup_enabled = false;
     if (touch_wakeup && wpin < GPIO_NUM_MAX)
     {
       if (M5.getBoard() == board_t::board_M5PaperS3)
       {
         // M5PaperS3 touch interrupt pin (GPIO48) is not RTC IO
         // and therefore not supported in EXT0 wakeup
-        gpio_wakeup_enable((gpio_num_t)wpin, gpio_int_type_t::GPIO_INTR_LOW_LEVEL);
-        esp_sleep_enable_gpio_wakeup();
+        pin_wakeup_enabled = (ESP_OK == gpio_wakeup_enable((gpio_num_t)wpin, gpio_int_type_t::GPIO_INTR_LOW_LEVEL))
+                          && (ESP_OK == esp_sleep_enable_gpio_wakeup());
       }
       else
       {
 #if SOC_PM_SUPPORT_EXT0_WAKEUP
-        esp_sleep_enable_ext0_wakeup((gpio_num_t)wpin, false);
+        pin_wakeup_enabled = (ESP_OK == esp_sleep_enable_ext0_wakeup((gpio_num_t)wpin, false));
         esp_sleep_pd_config(ESP_PD_DOMAIN_RTC_PERIPH, ESP_PD_OPTION_AUTO);
 #endif
       }
-      while (m5gfx::gpio_in(wpin) == false)
+      if (pin_wakeup_enabled)
+      {
+        while (m5gfx::gpio_in(wpin) == false)
+        {
+          m5gfx::delay(10);
+        }
+      }
+      else
       {
-        m5gfx::delay(10);
+        M5_LOGW("lightSleep: wakeup by GPIO%d is not enabled.", (int)wpin);
       }
     }
-    if (micro_seconds > 0){
+    if (micro_seconds != sleep_no_timer){
       esp_sleep_enable_timer_wakeup(micro_seconds);
     }else{
       esp_sleep_disable_wakeup_source(ESP_SLEEP_WAKEUP_TIMER);
+      if (!pin_wakeup_enabled)
+      { // Neither a timer nor a wakeup pin was configured by this call.
+        M5_LOGW("lightSleep: no timer or pin wakeup source is enabled.");
+      }
     }
     esp_light_sleep_start();
     if (M5.getBoard() == board_t::board_M5PaperS3)
diff --git a/src/utility/Power_Class.hpp b/src/utility/Power_Class.hpp
index 9b91e58..f443165 100644
--- a/src/utility/Power_Class.hpp
+++ b/src/utility/Power_Class.hpp
@@ -136,13 +136,20 @@ namespace m5
     /// @attention CoreInk と M5Paper は USB接続中はRTCタイマー起動が出来ない。;
     void timerSleep(const rtc_date_t& date, const rtc_time_t& time);
 
+    /// Value for micro_seconds of deepSleep / lightSleep, meaning "sleep without a timer wakeup".
+    /// The device sleeps until a wakeup pin or another wakeup source is triggered.
+    static constexpr std::uint64_t sleep_no_timer = ~0ull;
+
     /// ESP32 deepsleep
-    /// @param micro_seconds Number of micro seconds to wakeup.
-    void deepSleep(std::uint64_t micro_seconds = 0, bool touch_wakeup = true);
+    /// @param micro_seconds Number of micro seconds to wakeup. 0 = do not sleep. sleep_no_timer = no timer wakeup.
+    /// @param touch_wakeup Enable wakeup by the wakeup pin of the device, if it has one.
+    /// @attention Waking up from deep sleep restarts the program from the beginning.
+    void deepSleep(std::uint64_t micro_seconds = sleep_no_timer, bool touch_wakeup = true);
 
     /// ESP32 lightsleep
-    /// @param micro_seconds Number of micro seconds to wakeup.
-    void lightSleep(std::uint64_t micro_seconds = 0, bool touch_wakeup = true);
+    /// @param micro_seconds Number of micro seconds to wakeup. 0 = do not sleep. sleep_no_timer = no timer wakeup.
+    /// @param touch_wakeup Enable wakeup by the wakeup pin of the device, if it has one.
+    void lightSleep(std::uint64_t micro_seconds = sleep_no_timer, bool touch_wakeup = true);
 
     /// Get the remaining battery power.
     /// @return 0-100 level
diff --git a/src/utility/RTC_Class.cpp b/src/utility/RTC_Class.cpp
index 297ad66..f6e4376 100644
--- a/src/utility/RTC_Class.cpp
+++ b/src/utility/RTC_Class.cpp
@@ -69,7 +69,7 @@ namespace m5
 
     if (instance == nullptr)
     {
-      instance.reset(new PCF8563_Class(PCF8563_Class::DEFAULT_ADDRESS, 400000));
+      instance.reset(new PCF8563_Class(PCF8563_Class::DEFAULT_ADDRESS, 400000, i2c));
     }
 
     if (instance->begin())