Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

Kenneth — Tue, 02 Feb 2021 14:47:45 GMT

For the old S130 this was done differently, please check out:
https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v3.0.0/structble__conn__bw__counts__t.html

https://devzone.nordicsemi.com/f/nordic-q-a/21483/6-notifications-in-one-connection-interval-related-issue/84287#84287

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

brianreinhold — Tue, 02 Feb 2021 11:39:43 GMT

Okay, that is interesting. I automatically assumed that the entire connection interval would be used. In this case I am using the minimum MTU (developing a new standard and want to assure it works under minimal conditions) and letting the peer set the connection parameters (because as I understand it the central can do what it wants and ignore the peripheral's requests).

So what you are saying is that maybe the default configuration is not making full use of the connection interval. (occasionally I do get a 2 in the count). ... and I have the power to change this. Well, I'll certainly need to look into that!

Never mind! I am using SoftDevice s130 and according to the documentation the method sd_ble_cfg_set does not exist. There might be another way to do it, but I note that the ble_cfg structure does not exist either. Is there another way to do this in s130?

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

Kenneth — Tue, 02 Feb 2021 09:39:38 GMT

You should be able to get more than count=1 for each complete event, however it may be that you have not configured the BLE event to have time for more than 1 packet. You can find this thread useful on how to increase the event length:

https://devzone.nordicsemi.com/f/nordic-q-a/22698/setting-gap-connection-event-length---ble-hrs-c-demo

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

brianreinhold — Mon, 01 Feb 2021 19:30:26 GMT

One more question, if I send 5 packets by notifications in a loop how many BLE_EVT_TX_COMPLETE events will I get? It appears I will get 5. I was expecting to get 1 with a count of 5 in that event. How does this work? But I am never seeing a count greater than 1.

I have the feeling one has to do something like this

1. For every notification, increment a count by one

2. For every BLE_EVT_TX_COMPLETE event, decrement the count by the count returned in the event.

3. When 0, all indications have been sent.

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

Kenneth — Mon, 01 Feb 2021 17:32:39 GMT

Only indications.

Kenneth

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

brianreinhold — Mon, 01 Feb 2021 14:29:35 GMT

Will I ever get an NRF_ERROR_BUSY event using notifications or will that only happen on indications?

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

Kenneth — Mon, 01 Feb 2021 14:26:21 GMT

[quote user="brianreinhold"]do I have to send the same packet again AFTER the BLE_EVT_TX_COMPLETE event[/quote]

On any error you need to call sd_ble_gatts_hvx() with the same packet again later yes.

Kenneth

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

brianreinhold — Mon, 01 Feb 2021 09:28:35 GMT

In this case I don't think it would have helped. I was basing my code on what I understood the behavior of the API to be. On the air I tend to look at the packets, not the packets in a time sequence with respect to the connection intervals. (Im sure the front line sniffer can do this but that is not where I would be looking.) My problem was from the description of the method I assumed a one to one relation between call and event.

At the moment I still don't know what happens when I make the call and get a BLE_ERROR_NO_TX_PACKETS response ... do I have to send the same packet again AFTER the BLE_EVT_TX_COMPLETE event or is it sufficient just to wait for the event and THEN send the next packet? At the moment I have not run into the problem as I have not had a sufficiently long sequence to run out of buffers.

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

Kenneth — Mon, 01 Feb 2021 08:38:24 GMT

Typically an on-air sniffer log, such as nRF sniffer, may be helpful to find what may be the limiting the throughput.

Kenneth

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

brianreinhold — Fri, 29 Jan 2021 22:03:16 GMT

I did an experiment where I changed indications to notifications and in all cases the data transfer was slower with notifications. I am trying to understand why.

In my case I have a long characteristic of 90 or so bytes that are either indicated one after the other or notified one after the other. When using indications I indicated one hunk (MTU = min size 23) waited for the Indication done event, BLE_GATTS_EVT_HVC, and indicated the next hunk and so on. In the notification case the procedure was the same except I waited for the BLE_EVT_TX_COMPLETE event before sending the next notification.

The wait procedure was the same in both cases, sd_app_evt_wait() and then on wake up do the sd_ble_evt_get() loop. All this was done in the main thread.

Its not the greatest test given the size of data indicated or notified was not that big, but in all cases the indication case was faster; completely unexpected. Is that some fluke about the handling of the TX buffers that makes it slower?

RE: Notifications: How to know who is consuming tx buffers, most efficient way of sending a sequence, what error conditions are received?

Kenneth — Thu, 28 Jan 2021 16:17:02 GMT

The softdevice will try to send packets as fast possible, depending on the connection parameters, peer capabilities, other procedures, and packet loss. The simplest may be to have an app_timer that run slightly faster than the connection interval, and just write sd_ble_gatts_hvx() until you receive an error code from the timeout handler. It is also possible to wait for BLE_EVT_TX_COMPLETE before calling sd_ble_gatts_hvx(), however that presumes you have called sd_ble_gatts_hvx() previously, else the BLE_EVT_TX_COMPLETE is not triggered. But both can work.

The NRF_ERROR_BUSY may happen if you are sending indications (not notifications).