applications: nrf5340_audio: Changed nrf_rtc_cc_get loop delay.

- OCT-3368
- The existing delay was not sufficient for certain sample rates.
- Timer capture is on FRAMESTART which is later than the ISR execution.

Signed-off-by: Kristoffer Rist Skøien <[email protected]>

Author: koffes

applications/nrf5340_audio/src/modules/audio_i2s.c

@@ -66,8 +66,8 @@ static void i2s_comp_handler(nrfx_i2s_buffers_t const *released_bufs, uint32_t s
 {
 	if ((status == NRFX_I2S_STATUS_NEXT_BUFFERS_NEEDED) && released_bufs &&
 	    i2s_blk_comp_callback && (released_bufs->p_rx_buffer || released_bufs->p_tx_buffer)) {
-		i2s_blk_comp_callback(audio_sync_timer_capture_get(), released_bufs->p_rx_buffer,
-				      released_bufs->p_tx_buffer);
+		i2s_blk_comp_callback(audio_sync_timer_frame_start_capture_get(),
+				      released_bufs->p_rx_buffer, released_bufs->p_tx_buffer);
 	}
 }
 

applications/nrf5340_audio/src/modules/audio_sync_timer.c

@@ -39,7 +39,7 @@ static uint8_t dppi_channel_i2s_frame_start;
 #define AUDIO_SYNC_LF_TIMER_I2S_FRAME_START_EVT_CAPTURE		NRF_RTC_TASK_CAPTURE_0
 #define AUDIO_SYNC_LF_TIMER_CURR_TIME_CAPTURE_CHANNEL		1
 #define AUDIO_SYNC_LF_TIMER_CURR_TIME_CAPTURE			NRF_RTC_TASK_CAPTURE_1
-#define CC_GET_CALLS_MAX					30
+#define CC_GET_CALLS_MAX					20
 
 static uint8_t dppi_channel_curr_time_capture;
 
@@ -107,44 +107,41 @@ uint32_t audio_sync_timer_capture(void)
 	return timestamp_from_rtc_and_timer_get(tick, remainder_us);
 }
 
-uint32_t audio_sync_timer_capture_get(void)
+uint32_t audio_sync_timer_frame_start_capture_get(void)
 {
 	uint32_t cc_get_calls = 0;
 	uint32_t tick = 0;
 	static uint32_t prev_tick;
 	uint32_t remainder_us = 0;
-	static uint32_t prev_remainder_us;
 
-	/* This function is called too soon after I2S frame start may
-	 * result in values not yet being updated in the *_cc_get calls.
-	 * Ref: OCT-2585. To ensure new values are fetched, they are
-	 * read in a while-loop with a timeout.
+	/* This ISR is called before the I2S FRAMESTART event which does timer capture,
+	 * resulting in values not yet being updated in the *_cc_get calls.
+	 * To ensure new values are fetched, they are read in a while-loop with a timeout.
+	 * Depending on variables such as sample frequency, this delay varies.
+	 * For 16 kHz sampling rate is about 20 us. Less for 24 kHz and 48 kHz.
+	 * Ref: OCT-2585 and OCT-3368.
 	 */
 
 	do {
 		tick = nrf_rtc_cc_get(audio_sync_lf_timer_instance.p_reg,
 				      AUDIO_SYNC_LF_TIMER_I2S_FRAME_START_EVT_CAPTURE_CHANNEL);
 		cc_get_calls++;
 		if (cc_get_calls > CC_GET_CALLS_MAX) {
-			LOG_WRN("Unable to get new CC value");
+			LOG_ERR("Unable to get new tick from nrf_rtc_cc_get");
 			break;
 		}
+		k_busy_wait(1);
 	} while (tick == prev_tick);
 
 	cc_get_calls = 0;
 
-	do {
-		remainder_us = nrf_timer_cc_get(
-			NRF_TIMER1, AUDIO_SYNC_HF_TIMER_I2S_FRAME_START_EVT_CAPTURE_CHANNEL);
-		cc_get_calls++;
-		if (cc_get_calls > CC_GET_CALLS_MAX) {
-			LOG_WRN("Unable to get new CC value");
-			break;
-		}
-	} while (remainder_us == prev_remainder_us);
+	/* The HF timer is cleared on every I2S frame. Hence, this value can be
+	 * the same many times in a row.
+	 */
+	remainder_us = nrf_timer_cc_get(NRF_TIMER1,
+					AUDIO_SYNC_HF_TIMER_I2S_FRAME_START_EVT_CAPTURE_CHANNEL);
 
 	prev_tick = tick;
-	prev_remainder_us = remainder_us;
 
 	return timestamp_from_rtc_and_timer_get(tick, remainder_us);
 }
@@ -217,7 +214,7 @@ static int audio_sync_timer_init(void)
 	/* Initialize capturing of current timestamps */
 	ret = nrfx_dppi_channel_alloc(&dppi, &dppi_channel_curr_time_capture);
 	if (ret - NRFX_ERROR_BASE_NUM) {
-		LOG_ERR("nrfx DPPI channel alloc error (I2S frame start) - Return value: %d", ret);
+		LOG_ERR("nrfx DPPI channel alloc error (I2S frame start): %d", ret);
 		return -ENOMEM;
 	}
 
@@ -233,7 +230,7 @@ static int audio_sync_timer_init(void)
 
 	ret = nrfx_dppi_channel_enable(&dppi, dppi_channel_curr_time_capture);
 	if (ret - NRFX_ERROR_BASE_NUM) {
-		LOG_ERR("nrfx DPPI channel enable error (I2S frame start) - Return value: %d", ret);
+		LOG_ERR("nrfx DPPI channel enable error (I2S frame start): %d", ret);
 		return -EIO;
 	}
 

applications/nrf5340_audio/src/modules/audio_sync_timer.h

@@ -32,6 +32,6 @@ uint32_t audio_sync_timer_capture(void);
  *
  * @retval The last captured timestamp of the audio sync timer.
  */
-uint32_t audio_sync_timer_capture_get(void);
+uint32_t audio_sync_timer_frame_start_capture_get(void);
 
 #endif /* _AUDIO_SYNC_TIMER_H_ */

doc/nrf/releases_and_maturity/known_issues.rst

@@ -2307,6 +2307,7 @@ The issues in this section are related to the :ref:`nrf53_audio_app` application
 
 OCT-3368: For 16 and 24 kHz, the application may repeatedly print "audio_sync_timer: Unable to get new CC value"
   This may cause degraded audio quality.
+  This issue is a related to issue OCT-2585 and it shows the same behavior.
 
 .. rst-class:: v3-0-2 v3-0-1 v3-0-0 v2-9-0-nRF54H20-1 v2-9-1 v2-9-0 v2-8-0