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.
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;
heart_rate = (uint16_t)ble_sensorsim_measure(&m_heart_rate_sim_state, &m_heart_rate_sim_cfg);
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)
else if (err_code != NRF_SUCCESS)
// 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:
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;
Thank you for the Information. I have a Evaluation kit from Nordic and the sample code for HRS. I need to modify the sample code to send 20 bytes per connection interval instead of 2 bytes send by the existing code. Kindly help us how to change in the existing sensor code and view the same using the Master Control Panel.
I've extended my answer above somewhat to show how this can be done. Please make sure to take a look.
Thanks for this example. I got it working at 6580 bytes per second in a setup with a minimum connection interval of 10ms, and a timer interval of 10ms stuffing 20 bytes packets until it receives the BLE_ERROR_NO_TX_BUFFERS.
Just what I needed :-)
I need to transfer100KB of data in 1 sec. Is it possible?
How many TX Buffers available in the Softdevice stack ? Where can I get the information regarding the available TX buffers and RX Buffers.
I want to create 4 characteristic and send all 4 characterstic at a time in a single connection Interval of 10ms. To do this, I need to know before filling the new data to characteristic that data is transmitted on the air to avoid overwriting the existing data.