s140 - GATTS Handle Value Notification

RE: s140 - GATTS Handle Value Notification

Nikosant03 — Fri, 18 Dec 2020 06:55:39 GMT

Thank you for your support Hung!!

RE: s140 - GATTS Handle Value Notification

Hung Bui — Thu, 17 Dec 2020 17:10:33 GMT

Correct :)

RE: s140 - GATTS Handle Value Notification

Nikosant03 — Thu, 17 Dec 2020 15:28:56 GMT

Very nice flow!! Thanks a lot for your advice and your time!!

If I want to transmit every lets say 20ms then the interrupt at the start of the flow will be actually a timer right?

RE: s140 - GATTS Handle Value Notification

Hung Bui — Thu, 17 Dec 2020 14:44:10 GMT

Yes, if you have more packet queued than the number of packets being sent you will have NRF_ERROR_RESOURCE.

I don't see much point of keeping a timer in this case.

You can think of doing something like this:

RE: s140 - GATTS Handle Value Notification

Nikosant03 — Wed, 16 Dec 2020 15:13:26 GMT

Thank you Hung, now things are much more clear to me

[quote userid="2121" url="~/f/nordic-q-a/69440/s140---gatts-handle-value-notification/285261#285261"] In the code, you can just break after you receive NRF_ERROR_RESOURCES. After that you wait for BLE_GATTS_EVT_HVN_TX_COMPLETE[/quote]

Using a timer something like that I believe should be fine right?

I believe the reason that could cause the sd buffer to get full is in case that buffering happens faster than the packet transmission, right? So, what are the possible reasons that could cause the packet to not be transmitted and remain in the sd buffer causing high queuing and finally NRF_ERROR_RESOURCES?

RE: s140 - GATTS Handle Value Notification

Hung Bui — Wed, 16 Dec 2020 09:43:55 GMT

[quote user="Nikosant03"]So the sd buffer holds the packets that are going to be transmitted while the ATT table holds the information regarding the attributes (services, characteristics, descriptors) such as handle, UUID, and ATT value, right?[/quote]

==> Correct

[quote user="Nikosant03"]So despite that sd_ble_gatts_hvx() may return NRF_ERROR_RESOURCES the value of ATT table will be updated (I do not understand the reason behind that..). The ATT table value is updated for every sd_ble_gatts_hvx() call regardless if it was success or not?[/quote]

==> Correct, please check the description of sd_ble_gatts_hvx() function in ble_gatts.h

[quote user="Nikosant03"]Meaning that the buffer was full at that specific moment in time due to other activities? So I believe that before buffering app_value_4 a BLE_GATTS_EVT_HVN_TX_COMPLETE event had preceded right?[/quote]

==> Yes. It could be a write command has been executed. or a notification previously queued now sent.

[quote user="Nikosant03"]Something like that?[/quote]

In the code, you can just break after you receive NRF_ERROR_RESOURCES. After that you wait for BLE_GATTS_EVT_HVN_TX_COMPLETE . When you receive that event, you can call the loop again, or you can turn on a flag to continue the loop (of course you shouldn't wait infinitely in a loop wait for that event, should better put the CPU to sleep).

[quote user="Nikosant03"]The return value is the number of packets was sent in the same connection event?[/quote]

==> Correct, in the last connect event.

RE: s140 - GATTS Handle Value Notification

Nikosant03 — Tue, 15 Dec 2020 20:08:09 GMT

Hi Hung and thank you for your answer!!

[quote userid="2121" url="~/f/nordic-q-a/69440/s140---gatts-handle-value-notification/284848#284848"]The softdevice buffers are the buffers for the out going packets, the notification packets for example. When the ATT table is the table that store the value of the attribute locally[/quote]

I think that this is clear to me. So the sd buffer holds the packets that are going to be transmitted while the ATT table holds the information regarding the attributes (services, characteristics, descriptors) such as handle, UUID, and ATT value, right?

So despite that sd_ble_gatts_hvx() may return NRF_ERROR_RESOURCES the value of ATT table will be updated (I do not understand the reason behind that..). The ATT table value is updated for every sd_ble_gatts_hvx() call regardless if it was success or not?

[quote userid="2121" url="~/f/nordic-q-a/69440/s140---gatts-handle-value-notification/284848#284848"]For example in the Variant #1 case you pointed to, the sd_ble_gatts_hvx(app_value_3) returned ERR_RESOURCE[/quote]

Meaning that the buffer was full at that specific moment in time due to other activities? So I believe that before buffering app_value_4 a BLE_GATTS_EVT_HVN_TX_COMPLETE event had preceded right?

[quote userid="2121" url="~/f/nordic-q-a/69440/s140---gatts-handle-value-notification/284848#284848"]So basically, what you do is to call sd_ble_gatts_hvx() until you receive NRF_ERROR_RESOURCES , then you wait for BLE_GATTS_EVT_HVN_TX_COMPLETE event, and continue calling sd_ble_gatts_hvx()[/quote]

Something like that?

#define QUEUE_SIZE 4


// after the app_timer expire buffer 4 notifications
for (uint8_t i = 0; i < QUEUE_SIZE; i++) {

  error_code = sd_ble_gatts_hvx();
  // error filtering
  if (error_code != NRF_ERROR_RESOURCES) {
    APP_ERROR_CHECK(error_code);
  }
}

[quote userid="2121" url="~/f/nordic-q-a/69440/s140---gatts-handle-value-notification/284848#284848"]You can read the value return in the BLE_GATTS_EVT_HVN_TX_COMPLETE to know how many sd_ble_gatts_hvx() you should call.[/quote]

The return value is the number of packets was sent in the same connection event?

Thanks

Nick

RE: s140 - GATTS Handle Value Notification

Hung Bui — Mon, 14 Dec 2020 15:35:27 GMT

Hi Nick,

There is a difference between "Att table" and the softdevice buffers. They are not the same. The softdevice buffers are the buffers for the out going packets, the notification packets for example. When the ATT table is the table that store the value of the attribute locally. They are not the same. For example in the Variant #1 case you pointed to, the sd_ble_gatts_hvx(app_value_3) returned ERR_RESOURCE (for some reasons, explained later) then that mean the notification for app_value_3 will not be queued, but the value in the att_table is still updated.
And then the next call for sd_ble_gatts_hvx(app_value_4) success and the notification packet will be queued, and the local att_table is updated. Only 3 notification packets will be sent.

It's true that you can send 6 packets (or even more) in one connection interval, but there is no guarantee that you always can send 6 packets. If the event length is not configured long enough for such many packets, or if the peer device doesn't want to take multiple packet, you will have less. Also the buffer size can be 6 (or more) but it can be other activities that require some of the buffers. So you may have less number of the notification packet you can queue.

Even if a packet is queued, there is no guarantee that it will be sent in the next connection event. As I mentioned, the peer device may only accept 1 packet per connection event. This answer your question on why in variant #2 app_value_1 and app_value_2 is not sent at the same connection event.

When you receive BLE_GATTS_EVT_HVN_TX_COMPLETE () there is a chance that you can queue more packet, but it's not 100% sure you can, because there could be some other activity that already take the buffer (for example if you have other activity that add a write command, write command and notification send the same buffers).

So basically, what you do is to call sd_ble_gatts_hvx() until you receive NRF_ERROR_RESOURCES , then you wait for BLE_GATTS_EVT_HVN_TX_COMPLETE event, and continue calling sd_ble_gatts_hvx(). You can read the value return in the BLE_GATTS_EVT_HVN_TX_COMPLETE to know how many sd_ble_gatts_hvx() you should call. Or you can just simply call that function until you receive NRF_ERROR_RESOURCES.