BLE Throughput

RE: BLE Throughput

Einar Thorsrud — Thu, 17 Mar 2022 07:27:43 GMT

[quote user="kai19960504"]So the setting value of Event length is best equal to connection interval?[/quote]

If the goal is maximal throughput with a single connection, then yes.

RE: BLE Throughput

kai19960504 — Thu, 17 Mar 2022 00:31:43 GMT

Hi Einar,

[quote userid="7377" url="~/f/nordic-q-a/84813/ble-throughput/358221#358221"]like ensure the event length is equal the connection interval[/quote]

I currently make the event length equal to the connection interval according to your method. After testing several times, the problem of packet loss does not occur.

So the setting value of Event length is best equal to connection interval?

RE: BLE Throughput

Einar Thorsrud — Tue, 15 Mar 2022 13:16:33 GMT

[quote user="kai19960504"]If it does not return successfully, it means the buffer is full.[/quote]

Yes, if sd_ble_gatts_hvx() returns NRF_ERROR_RESOURCES it means the buffer is full. It can also return other error codes though, so you should not assume that all errors indicate that the queue is full.

[quote user="kai19960504"]I have also increased the length of NRF_SDH_BLE_GAP_EVENT_LENGTH but it still drops packets.[/quote]

OK. There are things you can do (like ensure the event length is equal the connection interval, and that it is of sensible length). But there will be a limit to the throughput. And if you try to send more then the link can handle, you will get NRF_ERROR_RESOURCES returned from sd_ble_gatts_hvx(). That is expected.

RE: BLE Throughput

kai19960504 — Tue, 15 Mar 2022 00:55:40 GMT

Hi Einar,

static ret_code_t error_messages_send(ble_gatts_hvx_params_t * const p_hvx_params,  uint16_t conn_handle)
{
    ret_code_t err_code = sd_ble_gatts_hvx(conn_handle, p_hvx_params);
    if (err_code == NRF_SUCCESS)
    {
        //NRF_LOG_INFO("Error notification has been sent using conn_handle: 0x%04X", conn_handle);
         NRF_LOG_INFO("OK   : %x",AppData_CNT++);
    }
    else
    {
        //NRF_LOG_DEBUG("Error: 0x%08X while sending notification with conn_handle: 0x%04X",
        //              err_code,
        //              conn_handle);
        NRF_LOG_INFO("Fail : %x",AppData_CNT++);
    }
    return err_code;
    
}

I checked some stuff about sd_ble_gatts_hvx().

If it does not return successfully, it means the buffer is full.

I have also increased the length of NRF_SDH_BLE_GAP_EVENT_LENGTH but it still drops packets.

RE: BLE Throughput

kai19960504 — Thu, 03 Mar 2022 09:18:31 GMT

Hi Einar,

I roughly understand what you mean, but I don't have a clue how to draw a conclusion at the moment, so I won't close this discussion at this time

RE: BLE Throughput

Einar Thorsrud — Wed, 02 Mar 2022 11:54:26 GMT

With a sniffer you can see how many packets are exchanged per connection event. That does not necessarily tell you what the maximum for a specific device is, as this is not a parameter in BLE as such, and that is exchanged on air. There could be other reasons for the number of packets not being as high as you expected (for instance, that you do not have enough data to send fast enough, of that one of the devices also needs to do other things like have time for other Bluetooth connections or WiFi, etc.)

RE: BLE Throughput

kai19960504 — Wed, 02 Mar 2022 06:33:26 GMT

Hi Einar,

So through Sniffer, I can confirm the maximum Packet that a Connection Interval can transmit, right?

RE: BLE Throughput

Einar Thorsrud — Tue, 01 Mar 2022 11:52:41 GMT

You were asking how to interpret the picture which shows that different phone models support a different set of packets per connection event. This does shows exactly that, but nothing else. This is implementation specific limitations in those devices, and not a general limitation. There is no defined maximum number of packets per connection event in the Bluetooth specification, nor in Nordic's BLE stacks.

In a nutshell: The picture tells you what those phones are capable of with regards to packets per connection, and nothing more.

RE: BLE Throughput

kai19960504 — Tue, 01 Mar 2022 00:42:21 GMT

Hi Einar,

[quote userid="7377" url="~/f/nordic-q-a/84813/ble-throughput/354979#354979"]This is entirely implementation specific though, and there is no such limitation in the Bluetooth specification. And for nRF devices there is no limit.[/quote]

I'm not very sure what you mean?

RE: BLE Throughput

Einar Thorsrud — Fri, 25 Feb 2022 10:06:45 GMT

Different devices may have different limitations. this shows that some different phone models have a limit of packets per connection event. This is entirely implementation specific though, and there is no such limitation in the Bluetooth specification. And for nRF devices there is no limit.

RE: BLE Throughput

kai19960504 — Fri, 25 Feb 2022 00:21:05 GMT

So,how to interpret this picture?

RE: BLE Throughput

Einar Thorsrud — Thu, 24 Feb 2022 08:19:29 GMT

There is no hard limit of 6 packets per connection event. If there is more data to send, there is time left in the event, and there are no retransmissions, you can send even more packets than that per event.

RE: BLE Throughput

kai19960504 — Thu, 24 Feb 2022 00:26:07 GMT

Hi Einar,

I have checked a lot of information, and it shows that many packets can be sent, but I can only receive up to 6 packets per connection interval. Is this correct?

RE: BLE Throughput

Einar Thorsrud — Thu, 17 Feb 2022 07:15:20 GMT

Hi Kai,

That was my bad. I did not realize that you only included parts of the table. I see now that this is the upper few rows of Table 1 under Bluetooth Low Energy data throughput in the latest SoftDevice Specification.

RE: BLE Throughput

kai19960504 — Thu, 17 Feb 2022 00:21:22 GMT

[quote userid="7377" url="~/f/nordic-q-a/84813/ble-throughput/353453#353453"]infocenter.nordicsemi.com/.../quote]

The content of v7.3.0 is like the picture when I asked the question, I don't understand what you said "Note that the documentation you refer to is for an old SoftDevice."

[/quote]

RE: BLE Throughput

Einar Thorsrud — Wed, 16 Feb 2022 18:03:39 GMT

[quote user="kai19960504"]

Could you please provide the latest S132 SPEC?

[/quote]

https://infocenter.nordicsemi.com/topic/struct_nrf52/struct/s132.html

[quote user="kai19960504"]Else question is 1 packet have 20byte,how long will that packet take?[/quote]

Which exact time are you after here? If this is 20 payload bytes, you would see about 272 us on air. The SIG has a page which may be interesting for you: How Fast Can It Be?

RE: BLE Throughput

kai19960504 — Wed, 16 Feb 2022 13:45:28 GMT

Could you please provide the latest S132 SPEC?

Else question is 1 packet have 20byte,how long will that packet take?

RE: BLE Throughput

Einar Thorsrud — Wed, 16 Feb 2022 13:41:58 GMT

It means that you have 6 ms that you can spend to transfer packets, but there is no need to spend the entire 6 ms (though that is not a very long time). You can also send several short packets or a single long. Here you don't use data length extension, so you can send several short packets. This is handled by the Bluetooth stack though, so you cannot do anything other than to try to send as much data a possible so that the stack always has more data to send.

RE: BLE Throughput

kai19960504 — Wed, 16 Feb 2022 13:32:22 GMT

Hi Einar,

Here is my sdk_config.h setting

Now NRF_SDH_BLE_GAP_EVENT_LENGTH is 6,so my packet will transfer total 6ms?

RE: BLE Throughput

Einar Thorsrud — Wed, 16 Feb 2022 13:22:24 GMT

Hi,

The event length is a Bluetooth concept. A connection event occurs every connection interval, and the duration of it is defined by the event length. During the event length, packets can be exchanged. If the event length is as long as the connection interval, packets can be exchanged more or less continuously. This maximises throughput.

[quote user=""]If the event length equal 7.5ms,does it mean that it can transmit 6 packets?[/quote]

Yes and no. If you cant fit 6 packets, then yes. If you can fit more, then you can send more. There is no defined maximum. Note that the documentation you refer to is for an old SoftDevice. More recent SoftDevice versions does not have this bandwidth configuration, but instead just allows you to configure the event length, using NRF_SDH_BLE_GAP_EVENT_LENGTH as you have found.