Add hello_sleep_alarm

Might get rid of all the RTC examples - why use RTC?

sleep/hello_sleep/CMakeLists.txt

@@ -1,8 +1,17 @@
-add_executable(hello_sleep
-        hello_sleep.c
+add_executable(hello_sleep_rtc
+        hello_sleep_rtc.c
         )
+target_link_libraries(hello_sleep_rtc
+        pico_stdlib
+        hardware_sleep
+        )
+pico_add_extra_outputs(hello_sleep_rtc)
 
-target_link_libraries(hello_sleep pico_stdlib hardware_sleep)
-
-# create map/bin/hex file etc.
-pico_add_extra_outputs(hello_sleep)
+add_executable(hello_sleep_alarm
+        hello_sleep_alarm.c
+        )
+target_link_libraries(hello_sleep_alarm
+        pico_stdlib
+        hardware_sleep
+        )
+pico_add_extra_outputs(hello_sleep_alarm)

sleep/hello_sleep/hello_sleep_alarm.c

@@ -0,0 +1,65 @@
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "pico/stdlib.h"
+#include "pico/sleep.h"
+#include "hardware/clocks.h"
+#include "hardware/pll.h"
+
+static bool awake;
+
+static void alarm_sleep_callback(uint alarm_id) {
+    printf("timer woke us up\n");
+    uart_default_tx_wait_blocking();
+    awake = true;
+
+    hardware_alarm_set_callback(alarm_id, NULL);
+    hardware_alarm_unclaim(alarm_id);
+}
+
+int main() {
+
+    stdio_init_all();
+
+    printf("Hello Alarm Sleep!\n");
+
+    do {
+        printf("Awake for 10 seconds\n");
+        sleep_ms(1000 * 10);
+
+        printf("Switching to XOSC\n");
+
+        // Wait for the fifo to be drained so we get reliable output
+        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("Switched to XOSC\n");
+
+        awake = false;
+
+        // Go to sleep until the alarm interrupt is generated after 10 seconds
+        printf("Sleeping for 10 seconds\n");
+        uart_default_tx_wait_blocking();
+
+        int alarm_id = -1;
+        sleep_goto_sleep_for(10000, &alarm_sleep_callback, &alarm_id);
+        if (alarm_id >= 0) {
+            // Make sure we don't wake
+            while (!awake) {
+                printf("Should be sleeping\n");
+            }
+        }
+
+        //Re-enabling clock sources and generators.
+        sleep_power_up();
+    } while(true);
+
+    return 0;
+}

sleep/hello_sleep/hello_sleep.c → sleep/hello_sleep/hello_sleep_rtc.c

@@ -56,7 +56,7 @@ int main() {
 
     stdio_init_all();
 
-    printf("Hello Sleep!\n");
+    printf("Hello RTC Sleep!\n");
 
     do {
         printf("Awake for 10 seconds\n");