Write request vs. indications

RE: Write request vs. indications

Kenneth — Tue, 08 May 2018 15:19:50 GMT

Do you have the possiblity to use the nRF sniffer and compare the two setups? Then we may identify the excact cause.

https://www.nordicsemi.com/eng/Products/Bluetooth-low-energy/nRF-Sniffer/(language)/eng-GB

You may also print all the BLE events to see if there is an event occuring here.

RE: Write request vs. indications

Sofie606 — Fri, 04 May 2018 13:30:23 GMT

Hi Kenneth,

The timing problem is solved now, it had to do with my own timers I set wrong.

Unfortunately I have a new problem now.

When I write to my slave device, I don't get a BLE_GATTS_EVT_WRITE event anymore, on my slave device.

I am still writing from my master device with sd_ble_gattc_write and I still get a BLE_GATTC_EVT_WRITE_RSP event, on my master device.

I tried writing to my slave device with the Master Control Panel. When I do that the BLE_GATTS_EVT_WRITE does occur. So I think it's my master device which has the problem.

Here is my code from my master device:

tx_wrs_message_t * p_msg;
uint16_t       cccd_val = true ? BLE_GATT_HVX_NOTIFICATION : 0;
   
p_msg              = &m_tx_wrs_buffer[m_tx_wrs_insert_index++];
m_tx_wrs_insert_index &= TX_WRS_BUFFER_MASK;
     
uint16_t wrs_write_handle = p_ble_write_request->peer_write_db.wrs_write_handle;
    
    
p_msg->req.write_req.gattc_params.handle   = wrs_write_handle;
p_msg->req.write_req.gattc_params.len      = WRITE_WRS_MESSAGE_LENGTH;
p_msg->req.write_req.gattc_params.p_value  = p_msg->req.write_req.gattc_value;
p_msg->req.write_req.gattc_params.offset   = 0;
p_msg->req.write_req.gattc_params.write_op = BLE_GATT_OP_WRITE_REQ;
p_msg->req.write_req.gattc_value[0]        = LSB_16(cccd_val);
p_msg->req.write_req.gattc_value[1]        = MSB_16(cccd_val);
p_msg->conn_handle                         = p_ble_write_request->conn_handle;
p_msg->type                                = WRITE_REQ_WRS;
    
   
if (m_tx_wrs_index != m_tx_wrs_insert_index)
{
          sd_ble_gattc_write(m_tx_wrs_buffer[m_tx_wrs_index].conn_handle,
                                          &m_tx_wrs_buffer[m_tx_wrs_index].req.write_req.gattc_params);
                   
          m_tx_wrs_index++;
          m_tx_wrs_index &= TX_WRS_BUFFER_MASK;
}

What could I be doing wrong?

Can you please help me?

RE: Write request vs. indications

Sofie606 — Fri, 04 May 2018 07:01:06 GMT

Hello Kenneth,

I need a response for my program. It's okay that it is slow, if I can estimate the time it takes :)

RE: Write request vs. indications

Kenneth — Thu, 03 May 2018 15:03:42 GMT

BLE_GATT_OP_WRITE_REQ is by design slow, since it rely BLE_GATTC_EVT_WRITE_RSP from the peer. I recommend to use the BLE_GATT_OP_WRITE_CMD instead if you need faster throughput.

RE: Write request vs. indications

Sofie606 — Thu, 03 May 2018 07:33:24 GMT

Hi Kenneth,

Thank you for your reaction.

I used the message sequence charts to explain what I mean.

The first image shows the timings I measured when I was sending an indication with sd_ble_gatts_hvx.

The time between sending the packet and receiving it on my central (client) was variable between 0 to 10 ms, just like I expected it would be. And the time between receiving the packet on my central (client) and getting the acknowlegde on my slave (server) took one connection interval (10ms) every time.

This is what I would expect to happen. And I also thought it would happen if I did it the other way around using a write request. But when I measured the time it took from sending the message from my central (client) to receiving it on my slave (server) it was one connection interval (10ms) every time.

Here is my code for calling sd_ble_gattc_write():

tx_message_t * p_msg;
    
uint16_t       cccd_val = true ? BLE_GATT_HVX_NOTIFICATION : 0;
    
p_msg              = &m_tx_buffer[m_tx_insert_index++];
m_tx_insert_index &= TX_BUFFER_MASK;

uint16_t cccd_handle = p_ble_write_request->conn_handle;

p_msg->req.write_req.gattc_params.handle   = cccd_handle;
p_msg->req.write_req.gattc_params.len      = WRITE_MESSAGE_LENGTH;
p_msg->req.write_req.gattc_params.p_value  = p_msg->req.write_req.gattc_value;
p_msg->req.write_req.gattc_params.offset   = 0;
p_msg->req.write_req.gattc_params.write_op = BLE_GATT_OP_WRITE_REQ;
p_msg->req.write_req.gattc_value[0]        = LSB_16(cccd_val);
p_msg->req.write_req.gattc_value[1]        = MSB_16(cccd_val);
p_msg->conn_handle                         = p_ble_write_request->conn_handle;
p_msg->type                                = WRITE_REQ;
    
if (m_tx_index != m_tx_insert_index)
{
    sd_ble_gattc_write(m_tx_buffer[m_tx_index].conn_handle,
                                          &m_tx_buffer[m_tx_index].req.write_req.gattc_params);
    m_tx_index++;
    m_tx_index &= TX_BUFFER_MASK;
    
}

Should the timings be the same of indication and write request?

Thank you :)

RE: Write request vs. indications

Kenneth — Wed, 02 May 2018 16:06:29 GMT

Hi,

The message sequence chart is as shown here:

http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v5.0.0/group___b_l_e___g_a_t_t_c___m_s_c.html?cp=2_3_1_1_1_2_2_3

What parameters are you using when calling sd_ble_gattc_write(.....)?