Slow Transfer - Calling ble_nus_string_send multiple times to send a large array

[kian79]

Hi all,

I am using PCA10040 with nRF5_SDK_14.2.0 and using the ble_app_uart example.

Basically I have a large array of size 18750 to send out and having read on the forum, I understand that I need to split up the data into smaller chunks and call ble_nus_string_send multiple times. Most people manage to get it to work by splitting into chuck of 20 bytes.

What I have tried so far is that I can provide a 150 byte array into the ble_nus_string_send function without any problem and its receiving well on a mobile phone. I also made a few changes:

#define MIN_CONN_INTERVAL MSEC_TO_UNITS(7.5, UNIT_1_25_MS) /**< Minimum acceptable connection interval (20 ms), Connection interval uses 1.25 ms units. */
#define MAX_CONN_INTERVAL MSEC_TO_UNITS(7.5, UNIT_1_25_MS) /**< Maximum acceptable connection interval (75 ms), Connection interval uses 1.25 ms units. */

Inside the gatt_init function, I also increase the max MUT size to 247:

err_code = nrf_ble_gatt_att_mtu_periph_set(&m_gatt, 247);

This is what I did in the main function:

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// Enter main loop.

for (;;)

{

UNUSED_RETURN_VALUE(NRF_LOG_PROCESS());

power_manage();

if(start_transfer)

{

start_transfer = false;

uint16_t length = 150;

uint8_t j = 0;

uint16_t k = 0;

for(j=0; j<125; j++)

{

do

{

err_code = ble_nus_string_send(&m_nus, mybuffer+k, &length);

if ( (err_code != NRF_ERROR_INVALID_STATE) && (err_code != NRF_ERROR_BUSY) )

{

APP_ERROR_CHECK(err_code);

}

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

// Enter main loop.
    for (;;)
    {
        UNUSED_RETURN_VALUE(NRF_LOG_PROCESS());
        power_manage();
			
				if(start_transfer)
				{
					start_transfer = false;
					uint16_t length = 150;
					uint8_t j = 0;
					uint16_t k = 0;
					for(j=0; j<125; j++)
					{
						do
						{	
							err_code = ble_nus_string_send(&m_nus, mybuffer+k, &length);
							if ( (err_code != NRF_ERROR_INVALID_STATE) && (err_code != NRF_ERROR_BUSY) )
							{
								APP_ERROR_CHECK(err_code);
							}
						} while (err_code == NRF_ERROR_BUSY);
						k = k + 150;
						while(!tx_complete);
						tx_complete = false;
					}
					
				}
    }

Each call to ble_nus_string_send, I am sending out 150 bytes, and I go this in a for loop that iterates for 125 times, so essentially I will transfer all 18750 bytes. After each call to ble_nus_string send, I am checking a flag tx_complete , which is set to true when a BLE_GATTS_EVT_HVN_TX_COMPLETE event happens. 

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case BLE_GATTS_EVT_HVN_TX_COMPLETE:

tx_complete = true;

break;

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

case BLE_GATTS_EVT_HVN_TX_COMPLETE:
	tx_complete = true;
	break;

This is working well except that the transfer seems to be still fairly slow about 19-20 seconds to send everything over. Is there anything I am doing wrong? How can I make this go much more faster?