[nrf fromtree] samples: boards: nrf: system_off: Print reset reason.

Add printing reset reason at the beginning of the sample. Makes it easier
to determine if sample correctly wakes up from LP mode.

Signed-off-by: Bartlomiej Buczek <[email protected]>
(cherry picked from commit c08edf7)

Author: nordic-babu

samples/boards/nordic/system_off/prj.conf

@@ -2,3 +2,4 @@ CONFIG_PM_DEVICE=y
 CONFIG_GPIO=y
 CONFIG_CRC=y
 CONFIG_POWEROFF=y
+CONFIG_HWINFO=y

samples/boards/nordic/system_off/sample.yaml

@@ -68,6 +68,7 @@ tests:
         - "Retained data not supported"
         - "Entering system off; wait 2 seconds to restart"
         - "system off demo"
+        - "Wakeup from System OFF by GRTC."
         - "Retained data not supported"
         - "Entering system off; wait 2 seconds to restart"
   sample.boards.nrf.system_off.retained_mem.grtc_wakeup:
@@ -97,6 +98,7 @@ tests:
         - "Off count: 1"
         - "Active Ticks:"
         - "Entering system off; wait 2 seconds to restart"
+        - "Wakeup from System OFF by GRTC."
   sample.boards.nrf.system_off.lpcomp_wakeup:
     extra_args: DTC_OVERLAY_FILE="boards/nrf54l15dk_nrf54l15_cpuapp_comparator.overlay"
     platform_allow:

samples/boards/nordic/system_off/src/main.c

@@ -11,6 +11,7 @@
 
 #include <zephyr/device.h>
 #include <zephyr/drivers/gpio.h>
+#include <zephyr/drivers/hwinfo.h>
 #include <zephyr/drivers/comparator.h>
 #include <zephyr/kernel.h>
 #include <zephyr/pm/device.h>
@@ -28,6 +29,20 @@ static const struct gpio_dt_spec sw0 = GPIO_DT_SPEC_GET(DT_ALIAS(sw0), gpios);
 static const struct device *comp_dev = DEVICE_DT_GET(DT_NODELABEL(comp));
 #endif
 
+void print_reset_cause(void)
+{
+	uint32_t reset_cause;
+
+	hwinfo_get_reset_cause(&reset_cause);
+	if (reset_cause & RESET_DEBUG) {
+		printf("Reset by debugger.\n");
+	} else if (reset_cause & RESET_CLOCK) {
+		printf("Wakeup from System OFF by GRTC.\n");
+	} else  {
+		printf("Other wake up cause 0x%08X.\n", reset_cause);
+	}
+}
+
 int main(void)
 {
 	int rc;
@@ -39,6 +54,7 @@ int main(void)
 	}
 
 	printf("\n%s system off demo\n", CONFIG_BOARD);
+	print_reset_cause();
 
 	if (IS_ENABLED(CONFIG_APP_USE_RETAINED_MEM)) {
 		bool retained_ok = retained_validate();
@@ -98,6 +114,7 @@ int main(void)
 		retained_update();
 	}
 
+	hwinfo_clear_reset_cause();
 	sys_poweroff();
 
 	return 0;