dealing large data packet's through ble

Question

Hi,
I need to send(using BLE) large amount of data's, which are collected by the accelerometer sensor for 1 hour. I have an external NOR flash where the accelerometer data's are stored and from there data's are transmitted to the BLE stack when sync occurs. I am using nRF51822 nordic controller. Assume that, data size will be 50KB. 
 Regards,
Balaji

Ole Morten · Accepted Answer

The easiest way to send large amounts of data is to send them sequentially as notifications. 
 Add a characteristic that is 20 bytes long and has the notify property. Split your data in 20 byte chunks and call sd_ble_gatts_hvx() repeatedly until you get the BLE_ERROR_NO_TX_BUFFERS back. At that time, wait until you get a BLE_EVT_TX_COMPLETE, at which point you again can send data until you get the BLE_ERROR_NO_TX_BUFFERS. Repeat until all data has been sent. 
 Edit: Following is a code snippet that shows how this could be done: 
 
static void heart_rate_meas_send(void)
{
 static uint32_t cnt = 0;
 uint32_t err_code;
 uint16_t heart_rate;
 
 while (true)
 {
 heart_rate = (uint16_t)ble_sensorsim_measure(&m_heart_rate_sim_state, &m_heart_rate_sim_cfg);

 cnt++;
 err_code = ble_hrs_heart_rate_measurement_send(&m_hrs, heart_rate);
 if (err_code == BLE_ERROR_NO_TX_BUFFERS ||
 err_code == NRF_ERROR_INVALID_STATE || 
 err_code == BLE_ERROR_GATTS_SYS_ATTR_MISSING)
 {
 break;
 }
 else if (err_code != NRF_SUCCESS) 
 {
 APP_ERROR_HANDLER(err_code);
 }
 
 // Disable RR Interval recording every third heart rate measurement.
 // NOTE: An application will normally not do this. It is done here just for testing generation
 // of messages without RR Interval measurements.
 m_rr_interval_enabled = ((cnt % 3) != 0);
 }
}

 
 and then in the event handler on_ble_evt: 
 
 case BLE_EVT_TX_COMPLETE:
 heart_rate_meas_send();
 break;

 
 You'd also have to add a call to hear_rate_meas_send() somewhere after a connection has been established and the CCCD written, to actually start the transmission (or do something else that triggers a TX_COMPLETE). 
 To maximize throughput, you'd also have to change the size of the characteristic to be 20 bytes. This is done by setting the max_len field of the ble_gatts_attr_t struct, and possibly vlen in ble_gatts_attr_md_t for the characteristic to be variable length. This is done on lines 228 and 237 in ble_hrs.c: 
 
 attr_md.vlen = 1;
 [...]
 attr_char_value.max_len = MAX_HRM_LEN;

dealing large data packet's through ble

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