Use digital pin for wake-up on C33

Author: sebromero

examples/Standby_WakeFromPin/Standby_WakeFromPin.ino

@@ -4,8 +4,12 @@
     This sketch demonstrates how you can use the Arduino_PowermManagement library to send a board to standby mode by using a GPIO pin and wake it up from another. 
     This sketch is universal and worksn on both Portenta C33 and H7. 
 
-    On the the Portenta C33 you can select any of the supported pins (A0, A1, A2, A3, A4, A5, D4, D7) to wake up the board from standby mode, 
-    but on the Portenta H7 only GPIO0 can be used to wake up the board from standby mode. GPIO0 is available through the High Density Connectors and you need a breakout board to access it. 
+    On the the Portenta C33 you can select any of the supported pins (A0, A1, A2, A3, A4, A5, D4, D7) to wake up the board from standby mode.
+    However setAllPeripheralsPower(false) in this sketch turns off the power lane of the analog pins.
+    This means they cannot sink current and therefore cannot be used to wake up the device. 
+    Hency only D4 and D7 can be used to wake up the device in this configuration.
+
+    On the Portenta H7 only GPIO0 can be used to wake up the board from standby mode. GPIO0 is available through the High Density Connectors and you need a breakout board to access it. 
 
     Requirements:
         - Arduino Portenta C33, Arduino Portenta H7
@@ -15,10 +19,17 @@
     Usage:
         - Connect a button to GOTO_SLEEP_PIN and with a pull-up resistor to 3.3V
         - Connect a button to pin PORTENTA_C33_WAKEUP_PIN if you are using the Portenta C33 or GPIO0 if you are using a Portenta H7  and with a pull-up resistor to 3.3V 
-            (If you need information about how to wire the buttons check this link: https://docs.arduino.cc/built-in-examples/digital/Button/)
+          For maximum power saving use external pull-up resistors.
+          You will need to power them separately as the 3.3V pin on the board 
+          is turned off when the device goes to sleep and peripherals are turned off.
+          Alternatively, use pinMode(<pin>, INPUT_PULLUP) for the pins and connect the buttons to ground.
+          (If you need information about how to wire the buttons check this link: https://docs.arduino.cc/built-in-examples/digital/Button/)
+
         - Upload the provided sketch to the board
+          Note: On Portenta H7, you need to upload this sketch to both cores, the M7 and the M4 for it to work.
+                You can do so by selecting the M7 core and then the M4 core from the Tools menu in the "Target core" section.
         - Press the button connected to GOTO_SLEEP_PIN to put the board into standby mode
-        - Press the button connected to PORTENTA_C33_WAKEUP_PIN or GPIO0 to wake up the board from standby mode
+        - Press the button connected to PORTENTA_C33_WAKEUP_PIN or GPIO0 on Portenta H7 to wake up the board from standby mode
         - The LED will blink every second to show that the board is awake when not in standby mode
         
     Original author: C. Dragomir (http://arduino.cc)
@@ -28,14 +39,20 @@
 #include "Arduino_PowerManagement.h"
 
 
-#define PORTENTA_C33_WAKEUP_PIN A3
+#define PORTENTA_C33_WAKEUP_PIN D4
 #define GOTO_SLEEP_PIN D0
 
 volatile bool shouldGoToSleep = false;
 
 Board board; 
 
 void setup() {
+    // When uploading this sketch to the M4 core, it just goes to standby mode.
+    #if defined(ARDUINO_GENERIC_STM32H747_M4)
+      board.standByUntilWakeupEvent();
+      return;
+    #endif
+
     pinMode(LED_BUILTIN, OUTPUT);
 
     // Register the sleep and wake-up pins as inputs