BLE without codec

RE: BLE without codec

Kashyap23 — Thu, 15 May 2025 12:35:45 GMT

Will the retransmissions happen automatically using bt_gatt_notify() function or do we need to do it .can you suggest any example?In my case I am using DMA in I2S peripheral for reading data and I am updating data in BLE using memcpy but thing is I am not getting any error code every time I got 0 implies success but data is missing .Will DMA for mic effects with the BLE thread in BLE?

RE: BLE without codec

Kenneth — Thu, 15 May 2025 07:02:56 GMT

In BLE I would claim packets can't be lost, however they may be delayed due to retransmissions. As you increase distance the signal get weaker, while noise and interference is the same level, so the risk of packets needs to be retransmitted increase. In any case a nRF sniffer for BLE would show the problem in detail.

Kenneth

RE: BLE without codec

Kashyap23 — Wed, 14 May 2025 17:47:05 GMT

I will check it .But my doubt is when devices are near there is no loss when I increase the distance I can see loss.How can I conclude this?What can be operating range or distance of BLE at higher data rates?Will throughput effects without using codecs?Or using codec will solve the issue

RE: BLE without codec

Kenneth — Wed, 14 May 2025 12:26:38 GMT

If you are using normal BLE connection, then all packets should be reliably sent yes, in the order they are written, I don't see any reason that should fail here. You can connect a nRF sniffer for BLE and check if that can give some clue as to what is happening.

Kenneth

RE: BLE without codec

Kashyap23 — Wed, 14 May 2025 08:59:20 GMT

I couldn't able to get that .I am using i2s protocol for reading data from mics using 2 channel at 16k sampling rate ,I want to transmit that data over BLE ,If I am increasing devices distance I can see loss of packets but I am not getting any error codes everying it's getting only 0 if i check "bt_gatt_notify" ret code, so it seems like data is not updating into that ble unction proprly.I am using work queue to update data in ble for every 8 ms thread will execute and I will get 250 samples into buffer of mic ,it will be filled in 7.8 ms as per calculation(125x(1/16000)) as per 2 channel for frame i will gt 2 samples so it wll be 125 frames to get 250 samples.And i kept sequence number in first 2 bytes ,i am getting loss of some sequence numbers but I am not getting any error codes.will i2s_buff_read will work differently?

#define SAMPLES_PER_BLOCK   250
int32_t Pcm_In[SAMPLES_PER_BLOCK];
int16_t Pcm_Out[SAMPLES_PER_BLOCK];

    ret = i2s_buf_read(i2s_dev_rx, &Pcm_In, &block_size);
	if (ret < 0) {
		printk("Failed to read data: %d\n", ret);
		break;
	}
	copyBuffer(Pcm_In,Pcm_Out,SAMPLES_PER_BLOCK);
	ret = i2s_buf_write(i2s_dev_tx, Pcm_Out, block_size);
	if (ret < 0) {
		printk("Failed to write data: %d\n", ret);
		break;
	}


static void copyBuffer(int32_t *Buff_In,int16_t *Buff_Out,uint16_t number_of_samples)
{

	Buff_Out[0] = (int16_t)(data_counter & 0xFFFF);
    Buff_Out[1] = (int16_t)((data_counter >> 16) & 0xFFFF);
	for(int i = 2; i < number_of_samples; i++) 
	{

		Buff_Out[i]=(Buff_In[i]>>16 );
		
	}
	data_counter++;

}

static void send_data_work_handler(struct k_work *work)
{
    if (!current_conn || !atomic_get(&is_notification_enabled)) {
        goto reschedule;
    }
	

    memcpy(data, &Pcm_Out, sizeof(Pcm_Out));

    int err = bt_gatt_notify(current_conn, &custom_service.attrs[1],
                            data, sizeof(data));
    if (err!=0) {
        printk("Failed to send notification (err %d)\n", err);
    }

reschedule:
    k_work_schedule_for_queue(&app_work_q, &data_send_work, K_MSEC(8));
}

RE: BLE without codec

Kenneth — Tue, 13 May 2025 14:11:03 GMT

Hi,

I assume you are using isochronous channels?

If you are using isochronous channels you can add some forward error correction in each packet that for instance can allow the receiver to recover any potential lost packets, or you can choose to send the same packet more than once (adding redundancy in case packets are lost).

Kenneth