samples: nfc: block on semaphore instead of k_cpu_atomic_idle

Replace k_cpu_atomic_idle() with semaphore blocking in order to
allow idle thread take care of power management.
Related ticket: KRKNWK-21438

Signed-off-by: Marcin Gasiorek <marcin.gasiorek@nordicsemi.no>

Author: MarGasiorek

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -502,7 +502,10 @@ Networking samples
 NFC samples
 -----------
 
-|no_changes_yet_note|
+* :ref:`writable_ndef_msg` sample:
+
+  * Fixed a power consumption issue.
+    The main loop now blocks on a semaphore instead of using the :c:func:`k_cpu_atomic_idle` function, allowing the idle thread to handle power management after the read or write tag.
 
 nRF5340 samples
 ---------------

samples/nfc/writable_ndef_msg/src/main.c

@@ -44,6 +44,8 @@ static atomic_t op_flags;
 static uint8_t flash_buf[CONFIG_NDEF_FILE_SIZE]; /**< Buffer for flash update. */
 static uint8_t flash_buf_len; /**< Length of the flash buffer. */
 
+static K_SEM_DEFINE(nfc_write_sem, 0, 1);
+
 static void flash_buffer_prepare(size_t data_length)
 {
 	if (atomic_cas(&op_flags, FLASH_WRITE_FINISHED,
@@ -52,6 +54,7 @@ static void flash_buffer_prepare(size_t data_length)
 		memcpy(flash_buf, ndef_msg_buf, sizeof(flash_buf));
 
 		atomic_set(&op_flags, FLASH_BUF_PREP_FINISHED);
+		k_sem_give(&nfc_write_sem);
 	} else {
 		printk("Flash update pending. Discarding new data...\n");
 	}
@@ -119,8 +122,6 @@ static int board_init(void)
  */
 int main(void)
 {
-	printk("Starting Nordic NFC Writable NDEF Message sample\n");
-
 	/* Configure LED-pins as outputs. */
 	if (board_init() < 0) {
 		printk("Cannot initialize board!\n");
@@ -170,6 +171,7 @@ int main(void)
 	printk("Starting NFC Writable NDEF Message sample\n");
 
 	while (true) {
+		k_sem_take(&nfc_write_sem, K_FOREVER);
 		if (atomic_cas(&op_flags, FLASH_BUF_PREP_FINISHED,
 				FLASH_WRITE_STARTED)) {
 			if (ndef_file_update(flash_buf, flash_buf_len) < 0) {
@@ -180,8 +182,6 @@ int main(void)
 
 			atomic_set(&op_flags, FLASH_WRITE_FINISHED);
 		}
-
-		k_cpu_atomic_idle(irq_lock());
 	}
 
 fail: