Cannot build I2S echo application for NRF5340

[TomHe]

Hi, I am a beginner into the embedded audio space, and happened upon this board to use for our university project. Our team's current plan would be to produce audio directly on the board and play it through the headphone jack, but have not found much success with the NRF5340 Audio application, as it has a lot of integration with Bluetooth (which we don't need for now). Right now we just need a simple application that plays a tune on the board.

In my search I have found the I2S echo application, which seems like a simple start for our use case. However, when trying to build the application we encountered the following error:

-- Found BOARD.dts: C:/ncs/v2.6.2/zephyr/boards/arm/nrf5340_audio_dk_nrf5340/nrf5340_audio_dk_nrf5340_cpuapp.dts
-- Found devicetree overlay: boards/nrf5340dk_nrf5340_cpuapp.overlay
devicetree error: pinctrl-names property in /soc/peripheral@50000000/i2s@28000 in C:/ncs/v2.6.2/zephyr/misc/empty_file.c has 1 strings, expected 2 strings

This is our build configuration (all other options left as default):

SDK version:

Any help would be appreciated! Thanks!

[Alexander Svensen]

No problem, glad I could help

[TomHe]

Hi Alexander Svensen , ace.johnny , dejans Thanks for all the help so far! I have been poking around with using audio_i2s_start(), audio_i2s_blk_comp_cb_register(), and audio_i2s_stop() for continuous I2S audio streaming, and I've arrived at the following sample:

#include <zephyr/kernel.h>
#include <nrfx_clock.h>
#include <audio_i2s.h>
#include <macros_common.h>
#include <hw_codec.h>
#include <tone.h>

#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(main, CONFIG_MAIN_LOG_LEVEL);

#define CONFIG_LOGGING

#define BLK_PERIOD_US 1000

/* Number of audio blocks given a duration */
#define NUM_BLKS(d) ((d) / BLK_PERIOD_US)
/* Single audio block size in number of samples (stereo) */
/* clang-format off */
#define BLK_SIZE_SAMPLES(r) (((r)*BLK_PERIOD_US) / 1000000)

#define NUM_BLKS_IN_FRAME      NUM_BLKS(CONFIG_AUDIO_FRAME_DURATION_US)
#define BLK_MONO_NUM_SAMPS     BLK_SIZE_SAMPLES(CONFIG_AUDIO_SAMPLE_RATE_HZ)

#define BLK_MONO_SIZE_OCTETS   (BLK_MONO_NUM_SAMPS * CONFIG_AUDIO_BIT_DEPTH_OCTETS)

static uint8_t *tx_buf;
static uint32_t *rx_buf;

/* Alternate-buffers used when there is no active audio stream.
 * Used interchangeably by I2S.
 */
static struct {
	uint8_t __aligned(WB_UP(1)) buf_0[BLK_MONO_SIZE_OCTETS];
	uint8_t __aligned(WB_UP(1)) buf_1[BLK_MONO_SIZE_OCTETS];
	bool buf_0_in_use;
	bool buf_1_in_use;
} alt;

/**
 * @brief	Get first available alternative-buffer.
 *
 * @param	p_buffer	Double pointer to populate with buffer.
 *
 * @retval	0 if success.
 * @retval	-ENOMEM No available buffers.
 */
static int alt_buffer_get(void **p_buffer)
{
	if (!alt.buf_0_in_use) {
		alt.buf_0_in_use = true;
		*p_buffer = alt.buf_0;
	} else if (!alt.buf_1_in_use) {
		alt.buf_1_in_use = true;
		*p_buffer = alt.buf_1;
	} else {
		return -ENOMEM;
	}

	return 0;
}

/**
 * @brief	Frees both alternative buffers.
 */
static void alt_buffer_free_both(void)
{
	alt.buf_0_in_use = false;
	alt.buf_1_in_use = false;
}

static void i2s_block_complete_callback()
{
	/*** Data exchange ***/
	audio_i2s_set_next_buf(tx_buf, rx_buf);
}

int main(void) 
{
    int ret;

#ifdef CONFIG_LOGGING
    printk("\nLogging I2S Info ...\n");
    printk("\nCONFIG_I2S_LRCK_FREQ_HZ:     %d\n", CONFIG_I2S_LRCK_FREQ_HZ);
    printk("\nCONFIG_I2S_CH_NUM:           %d\n", CONFIG_I2S_CH_NUM);
    printk("\nCONFIG_AUDIO_BIT_DEPTH_BITS: %d\n", CONFIG_AUDIO_BIT_DEPTH_BITS);
#endif

	/* Use this to turn on 128 MHz clock for cpu_app */
	ret = nrfx_clock_divider_set(NRF_CLOCK_DOMAIN_HFCLK, NRF_CLOCK_HFCLK_DIV_1);
	ret -= NRFX_ERROR_BASE_NUM;
	if (ret) {
		return ret;
	}

	audio_i2s_blk_comp_cb_register(i2s_block_complete_callback);
	audio_i2s_init();

	ret = hw_codec_init();
	if (ret) {
		LOG_ERR("Failed to initialize HW codec: %d", ret);
		return ret;
	}
	hw_codec_volume_set(100);

	printk("\nStarting I2S!\n");

	/* Starting I2S */

	/********** I2S TX **********/
	ret = alt_buffer_get((void **)&tx_buf);
	ERR_CHK(ret);

	/********** I2S RX **********/
	ret = alt_buffer_get((void **)&rx_buf);
	ERR_CHK(ret);

	size_t tone_size;
	ret = tone_gen((uint16_t *)tx_buf, &tone_size, 1000, CONFIG_I2S_LRCK_FREQ_HZ, 1.0);
	if (ret || tone_size != BLK_MONO_SIZE_OCTETS) {
		LOG_ERR("Failed to generate test tone");
		return ret;
	}

	ret = hw_codec_default_conf_enable();
	ERR_CHK(ret);
	audio_i2s_start(tx_buf, rx_buf);
	
	k_msleep(5000);

	ret = hw_codec_soft_reset();
	ERR_CHK(ret);
	audio_i2s_stop();
	
	alt_buffer_free_both();

	printk("\nI2S Stopped!\n");

    return 0;
}

It basically re-uses the alt_buffer_get() function to first fetch empty buffers each of size BLK_MONO_SIZE_OCTETS since I do not want two channels. It then fills the tx_buf with a single period of sine wave via tone_gen. 

I know that: 

  BLK_MONO_SIZE_OCTETS = 32

  nCONFIG_I2S_LRCK_FREQ_HZ = 16000

 

  nCONFIG_I2S_CH_NUM = 1

  nCONFIG_AUDIO_BIT_DEPTH_BITS = 16

This means that a single tx_buf (which is of size 32bytes -> 16 samples), when filled with a single sine period, should play to 1000Hz. However, I am hearing 2000Hz when measuring with my device. I'm not sure if I've missed anything or did some steps wrong. I have attached the full project as a zip file if interested (there is a .git file inside so you can track all the changes I've made starting from the nrf5340_audio application). I would really appreciate some pointers and thanks again for your help!

i2s_sample-copy.7z