How to determine the number of packets per connection interval

RE: How to determine the number of packets per connection interval

Sigurd — Mon, 10 Feb 2020 09:15:29 GMT

[quote user="Harinben"]Are there any known reports that have measured the BLE throughput with the PCA10059 in combination with the pc-ble-driver?[/quote]

No, unfortunately not.

[quote user="Harinben"]Or are there any useful examples?[/quote]

For pc-ble-driver we have the heart_rate_collector and heart_rate_monitor example. For measuring throughput, we have the ble_app_att_mtu_throughput example in the SDK, but nothing on the pc-ble-driver side.

RE: How to determine the number of packets per connection interval

Harinben — Fri, 07 Feb 2020 08:44:11 GMT

The primary issue has been resolved for me. I will mark the correct answer.

But I have one last question. Are there any known reports that have measured the BLE throughput with the PCA10059 in combination with the pc-ble-driver? Or are there any useful examples?

RE: How to determine the number of packets per connection interval

Sigurd — Wed, 05 Feb 2020 14:34:27 GMT

[quote user="Harinben"]Because of this I achieve higher data throughput[/quote]

Great!

[quote user="Harinben"]Is it correct that the "Get"-function does not work?[/quote]

That is correct. sd_ble_opt_get is not supported for this option.

[quote user="Harinben"]Is this delay of the master fixed or can it be configured by a parameter?[/quote]

You cannot change this, it takes longer time to send a long packet.

RE: How to determine the number of packets per connection interval

Harinben — Wed, 05 Feb 2020 07:42:57 GMT

Sorry for the delay. I did some tests yesterday.

I was able to get several packets with MTU size 247 per connection interval sent yesterday. Because of this I achieve higher data throughput

As recommended I have looked at the option extended BLE connection event. It was already set on the firmware side. But I can't make an exact statement on the PC side (sd_api_v3), because the function

sd_ble_opt_get(BLE_COMMON_OPT_CONN_EVT_EXT, &opt);

returns an NRF_ERROR_NOT_SUPPORTED error. But the "Set"-function does not return an error, so I assume that it works. Is it correct that the "Get"-function does not work?

[quote userid="15146" url="~/f/nordic-q-a/57230/how-to-determine-the-number-of-packets-per-connection-interval/232405"]You are sending write commands from the master, and sending notifications from the slave? [/quote]

Right. To maximize the data throughput I decided to acknowledge the data with notifications on application level.

[quote userid="15146" url="~/f/nordic-q-a/57230/how-to-determine-the-number-of-packets-per-connection-interval/232405"]Could you save and upload the sniffer log ?[/quote]

Sure.

devzone.nordicsemi.com/.../7612.MTU_5F00_size_5F00_227.pcapng

devzone.nordicsemi.com/.../6138.MTU_5F00_size_5F00_247.pcapng

I noticed something else. In the sniffer data (MTU size 227) you can see that the slave answers with a lower latency (~1ms), but the master sends the next packet with a delay of >2ms. Is this delay of the master fixed or can it be configured by a parameter?

RE: How to determine the number of packets per connection interval

Sigurd — Mon, 03 Feb 2020 16:35:59 GMT

[quote user="Harinben"]If I have understood it correctly, it would be best if I set NRF_SDH_BLE_GAP_EVENT_LENGTH equal to connection interval. Correct?[/quote]

It depends. By setting it even higher you should be able to queue more packets.

You might also want to enable extended BLE connection events:

void conn_evt_len_ext_set(bool status)
{
    ret_code_t err_code;
    ble_opt_t  opt;

    memset(&opt, 0x00, sizeof(opt));
    opt.common_opt.conn_evt_ext.enable = status ? 1 : 0;

    err_code = sd_ble_opt_set(BLE_COMMON_OPT_CONN_EVT_EXT, &opt);
    APP_ERROR_CHECK(err_code);

}

[quote user="Harinben"]Is it possible that there is a limitation on the USB dongle firmware?[/quote]

There could be some added latency, but the MD-bit indicats the the SoftDevice had more data to send. You are sending write commands from the master, and sending notifications from the slave? Could you save and upload the sniffer log ?

RE: How to determine the number of packets per connection interval

Harinben — Mon, 03 Feb 2020 15:22:46 GMT

Hi,

Thank you for the quick response.

If I have understood it correctly, it would be best if I set NRF_SDH_BLE_GAP_EVENT_LENGTH equal to connection interval. Correct?

I have checked these parameters in my test setup. NRF_SDH_BLE_GAP_EVENT_LENGTH is set to 12 (*1.25ms = 15ms) in sdk_config.h. This value should also allow more than one packet with MTU size 247 bytes.

On the PC side, BLE_CONN_BW_HIGH is already set as suggested in your code snippet.

Is it possible that there is a limitation on the USB dongle firmware?

RE: How to determine the number of packets per connection interval

Sigurd — Mon, 03 Feb 2020 13:29:43 GMT

Hi,

For SoftDevice v.6.x, as long as packets are queued in the SoftDevice when the connection event starts, the Softdevice will try to send as many packets as it can in the the connection interval, as long as the time set aside for the connection on every connection interval is not exceeded, this limit can be configured with NRF_SDH_BLE_GAP_EVENT_LENGTH (in sdk_config.h), and as long as there is still packets in the queue.

For SoftDevice v.3, you can configure the bandwidth for the central like this (documentation here):

     /*Configure bandwidth */
 ble_opt_t ble_opt;
 ble_common_opt_conn_bw_t conn_bw;
 memset(&conn_bw, 0x00, sizeof(conn_bw));
 memset(&ble_opt, 0x00, sizeof(ble_opt));

 conn_bw.conn_bw.conn_bw_rx = BLE_CONN_BW_HIGH;
 conn_bw.conn_bw.conn_bw_tx = BLE_CONN_BW_HIGH;
 conn_bw.role = BLE_GAP_ROLE_CENTRAL;
 
 ble_opt.common_opt.conn_bw = conn_bw;
 
 uint32_t err_code = sd_ble_opt_set(BLE_COMMON_OPT_CONN_BW, &ble_opt);
 APP_ERROR_CHECK(err_code);