Maximum iso data length of NRF5340 audio increased

[LandyWang]

Hello,

I am using bis gateway on nrf5340 audio dk to transmit data.

In addition to audio encoded data, I also wanted to send some additional data, so I put these data after the audio encoded data and sent them together, and then I encountered the -EMSGSIZE error.

It seems that the maximum iso data length is 120, if the data length exceeds this size, it will not be transmitted.

Can this maximum length be increased?

[dejans]

Hi,

Do you use nrf5340_audio application? Can you show your changes?

Do you use I2S or USB?

Can you provide a full error log?

Best regards,
Dejan

[LandyWang]

Yes, I use nrf5340_audio application, and I use USB in.

Here are my changes, I increased the data length when sending it.

[audio_system.c]

static void encoder_thread(void *arg1, void *arg2, void *arg3)
{
    ...
    if (sw_codec_cfg.encoder.enabled) {
			/* Send encoded data over IPM */
			//streamctrl_encoded_data_send(encoded_data, encoded_data_size);
			streamctrl_encoded_data_send(my_data, 520);
		}
	STACK_USAGE_PRINT("encoder_thread", &encoder_thread_data);
	}
}

And I added the max data related log to iso_chan_max_data_len function in iso.c.

[iso.c]

static uint16_t iso_chan_max_data_len(const struct bt_iso_chan *chan,
				      uint32_t ts)
{
	...
	/* Update the max_data_len to take the max_controller_data_len into account */
	max_data_len = MIN(max_data_len, max_controller_data_len);
	BT_INFO("Max data len:%d",max_data_len);
	BT_INFO("Max Controller data len:%d",max_controller_data_len);

	return max_data_len;
}

This is the config I added in prj.conf.

CONFIG_BT_ISO_TX_MTU=2048
CONFIG_BT_ISO_RX_MTU=2048

Then this is my error log.

GW [00:00:00.130,798] <inf> bis_gateway: Broadcast source 0x2000bc78 started
GW [00:00:00.131,134] <inf> bis_gateway: Broadcast source 0x2000bc9c started
GW [00:00:11.588,470] <inf> bt_iso: Max data len:120
GW [00:00:11.588,470] <inf> bt_iso: Max Controller data len:1536
GW [00:00:11.588,470] <inf> bt_iso: Cannot send 520 octets, maximum 120
GW [00:00:11.588,470] <wrn> bis_gateway: Failed to send audio data: -122
GW [00:00:11.588,500] <wrn> streamctrl: Problem with sending LE audio data, ret: -122

[dejans]

Hi,

On the gateway, you could try to replace

BT_CODEC_LC3_QOS_10_UNFRAMED(251u, 4u,20u, LE_AUDIO_PRES_DELAY_US))

with 

BT_CODEC_LC3_QOS_10_UNFRAMED(251u, 2u,20u, LE_AUDIO_PRES_DELAY_US))

Generally, we highly recommend that you upgrade to the NCS v2.6.1 (or NCS v2.7.0 when it becomes available).

Best regards,
Dejan

[LandyWang]

Thanks for your assistance, it works.

Now I can successfully transfer 250 bytes of data through bis.

Then, I tried to increase the sdu size to 512 bytes. The following are my modifications on the gateway.

BT_CODEC_LC3_QOS_10_UNFRAMED(512u, 0u,20u, LE_AUDIO_PRES_DELAY_US))

I tried to send 480 bytes of data, written as follows:

streamctrl_encoded_data_send(my_data, 480);

Although the bis headset connect to the gateway successfully, it did not receive any data.

What is the limit on the data size that is bis gateway can transmit?

[dejans]

Hi,

I would need to check this internally. I will get back to you during next week.

Best regards,
Dejan

[dejans]

Hi,

The audio application currently supports max PDU (containing one SDU) of 251. 

Best regards,
Dejan

[LandyWang]

Ok, I see. Thank you for your assistance.

[dejans]

Hi,

I am glad to assist. Please let me know if you need any further assistance.

Best regards,
Dejan