Improve the dormant rtc example a bit

sleep/hello_dormant_rtc/hello_dormant_rtc.c

@@ -11,6 +11,10 @@
 #include "hardware/rtc.h"
 #include "hardware/clocks.h"
 
+// This example needs an external clock fed into the GP20
+// Note: Only GP20 and GP22 can be used for clock input, See the GPIO function table in the RP2040 datasheet.
+// You can use another Pico to generate this. See the clocks/hello_gpout example for more details.
+// clock_gpio_init(25, CLOCKS_CLK_GPOUT3_CTRL_AUXSRC_VALUE_CLK_RTC, 1);
 #define EXTERNAL_CLOCK_INPUT_PIN 20
 #define RTC_FREQ_HZ 46875
 
@@ -58,27 +62,30 @@ int main() {
 
     stdio_init_all();
     printf("Hello Dormant GPIO!\n");
-            
-    printf("Switching to XOSC\n");
-    uart_default_tx_wait_blocking();
+    while(true) {
+        printf("Awake for 10s\n");
+        sleep_ms(10000);
 
-    /*Set the crystal oscillator as the dormant clock source, UART will be reconfigured from here
-    This is necessary before sending the pico to sleep*/
-    sleep_run_from_xosc();
+        printf("Switching to XOSC\n");
+        uart_default_tx_wait_blocking();
 
-    printf("Running from XOSC\n");
-    uart_default_tx_wait_blocking();
+        /*Set the crystal oscillator as the dormant clock source, UART will be reconfigured from here
+        This is necessary before sending the pico to sleep*/
+        sleep_run_from_xosc();
 
-    printf("XOSC going dormant\n");
-    uart_default_tx_wait_blocking();
+        printf("Running from XOSC\n");
+        uart_default_tx_wait_blocking();
 
-    // Go to sleep until the RTC interrupt is generated after 10 seconds
-    rtc_sleep();
+        printf("XOSC going dormant\n");
+        uart_default_tx_wait_blocking();
 
-    //Re-enabling clock sources and generators.
-    sleep_power_up();
+        // Go to sleep until the RTC interrupt is generated after 10 seconds
+        rtc_sleep();
 
-    printf("ROSC restarted!\n");
+        //Re-enabling clock sources and generators.
+        sleep_power_up();
 
+        printf("ROSC restarted!\n");
+    }
     return 0;
 }