BLE_NUS_C how to send pkt from client to service with efficient and reliable?

RE: BLE_NUS_C how to send pkt from client to service with efficient and reliable?

Sigurd — Mon, 11 May 2020 14:42:24 GMT

The slave/server can only send data on it's own initiative using notification or indication. See this figure:

You can read more about difference between notification and indication in this post: https://devzone.nordicsemi.com/f/nordic-q-a/99/notification-indication-difference

This page about throughput might also be helpful for you: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsds_s132%2FSDS%2Fs1xx%2Fble_data_throughput%2Fble_data_throughput.html

RE: BLE_NUS_C how to send pkt from client to service with efficient and reliable?

Taoo — Thu, 07 May 2020 08:56:57 GMT

I see "nRF5_SDK_16.0.0\ble_peripheral\ble_app_uart" demo project.Demo slave send by call ble_nus_data_send

->sd_ble_gatts_hvx ,param with:BLE_GATT_HVX_NOTIFICATION

But there is no choose with write cmd or write request like master(central).How slave ensure reliable upload packet to master? Wheather SoftDevice to ensure notification is reliable send?

RE: BLE_NUS_C how to send pkt from client to service with efficient and reliable?

Taoo — Thu, 07 May 2020 08:31:57 GMT

First of all,Thanks for your reply!

1、I detect the packet loss by sending packet with one byte for sequence.Each packet will increase 1.In the slave,judge wheather sequence is continuous or not.

2、I understand throughput with write request is lower than write cmd.but how low?less than 500B/s for each slave？

3、Slave upload seem more reliable, even though throughput with 2KB/s.but slaves were bought from other company,I am not sure it used write request or write cmd.wheather some params I set in master are not proper.Or it is different from master(central) and slave(peripheral),that is the ultimate performance for master send packet to slave.

RE: BLE_NUS_C how to send pkt from client to service with efficient and reliable?

Sigurd — Wed, 06 May 2020 08:37:18 GMT

Hi,

How do you detect the packet loss ?

Are you using a custom board, or a nRF52832-DK in your test ?

As long as the sd_ble_gattc_write() returns NRF_SUCESS, the packet will be delivered to the server.

When transferring data with a write request from GATT client, then only one packet is sent every other connection event. This is because ATT level acknowledgement must be received for a sent packet before sending another packet. The procedure is as follows:

Connection event x: Send writeRequest packet
Connection event x+1: Receive ATT acknowledgement packet
Connection event x+2: Send writeRequest packet
Connection event x+3: Receive ATT acknowledgement packet

and so on. So with connection interval 7.5ms, then one packet can be sent every 15ms, therefore substantially limiting throughput.

But with Write Command packet you can send multiple packets each connection interval, and you will therefore get much higher throughput with Write Command.

RE: BLE_NUS_C how to send pkt from client to service with efficient and reliable?

Taoo — Wed, 06 May 2020 00:44:52 GMT

Is there any suggestion?

Do i describe clearly?

Hope for yours replies!