I give up; how do I do a service changed?

RE: I give up; how do I do a service changed?

tesc — Wed, 20 Nov 2019 16:33:42 GMT

Hi,

As pc-ble-driver is serialization of the same SoftDevice that is used by the nRF5 SDK, all code from the nRF5 SDK using the SoftDevice can be used for referencing how to use the SoftDevice API.

Regards,
Terje

RE: I give up; how do I do a service changed?

brianreinhold — Tue, 19 Nov 2019 11:28:17 GMT

this is the pc-ble-driver.

Following those examples does not solve the problem

RE: I give up; how do I do a service changed?

tesc — Wed, 13 Nov 2019 10:03:22 GMT

Hi,

Hung is out-of-office and I am having a look at this while he is away.

The file gatt_cache_manager.c is found in the SDK at <sdk root folder>/components/ble/peer_manager/gatt_cache_manager.c

Regards,
Terje

RE: I give up; how do I do a service changed?

brianreinhold — Fri, 08 Nov 2019 11:50:17 GMT

UI experience: The problem is the reply button doesnt' EXIST! I have to go through loops an hoops to get it to appear (refreshes and reloads). When it finally appears, all is rosy.

That aside, I do not have the tools to build the HEX files needed to test the example in the NRF SDK. The other problem is that I could not find the file you referenced in the SDK (at least in my copy). So I can't even look at it. I found something similar in another file and that is why I did the 'loop' over ever-increasing handles.

That 'loop-guess' part still stinks even if it DID work; not knowing what the handle of the service changed characteristic is, providing no means to get it, yet requiring it in the call to invoke the service changed indication.

Clearly there needs to be an sd_* call that gets the handle needed in the sd_ call that invokes the service changed. Doesn't that make sense? Otherwise DONT demand the handle and have the soft device find it. It clearly knows it!

In the end the problem is that softdevice thinks it doesn't have the system attributes. What that error means is still unclear to me because a get clearly shows they are there!

If it was TRULY the case that Android had not enabled indications I would expect the error

NRF_ERROR_INVALID_STATE

not

BLE_ERROR_GATTS_SYS_ATTR_MISSING

At least that's what the documentation says.

RE: I give up; how do I do a service changed?

Hung Bui — Fri, 08 Nov 2019 11:24:22 GMT

Hi Brian,

I'm sorry for the bad user experience. You can click on the Reply button right under the question.

The service_changed_send_in_evt() you can find in gatt_cache_manager.c. The file is used in the ble_app_gatts.
From what you described, it seems to be correct to me. Not sure why the function still complaining.

But I strongly suggest to try testing the ble_app_gatts and ble_app_gatts_c and then compare to the behavior of your application. Try comparing the difference in the code on the working examples with yours. I think you are pretty close.

RE: I give up; how do I do a service changed?

brianreinhold — Fri, 08 Nov 2019 10:19:33 GMT

where do I find service_changed_send_in_evt()?

As stated, my \examples\connectivity\ble_connectivity does nto have the code you referenced above

RE: I give up; how do I do a service changed?

brianreinhold — Fri, 08 Nov 2019 10:04:51 GMT

Just a note on this web app: The 'reply', verify answer, etc buttons/options often don't show up until I do many screen refreshes, especially on the last messages. If you have a 'reply' from an older message but not the last message, hitting the reply there makes the buttons appear on the last message. Nothing do to with this thread but it makes participation annoying and sometimes 'come back later to try'.

Back to the issue:

Turns out Android auto-handles service changed because I handled it too and I wrote a trap in my Nordic peripheral to catch all descriptor writes and I was writing the service changed CCCD twice (and the heart rate measurement once).

I have this code to catch the descriptor-writing attempts by the Android

case BLE_GATTS_EVT_WRITE:
    if (p_ble_evt->evt.gatts_evt.params.write.handle ==
            m_heart_rate_measurement_handle.cccd_handle)
    {
        uint8_t write_data = p_ble_evt->evt.gatts_evt.params.write.data[0];
        m_send_notifications = (write_data == BLE_GATT_HVX_NOTIFICATION);
        cccdSet = m_send_notifications;
		printf("Enabling CCCD with %d at time %llu\n", write_data, (GetTickCount64() - elapsedTimeStart));
    }
    else
    {
        uint8_t write_data = p_ble_evt->evt.gatts_evt.params.write.data[0];
            printf("Client Enabling CCCD of characeteristic handle %d with value %d at time %llu\n",
                p_ble_evt->evt.gatts_evt.params.write.handle, write_data, (GetTickCount64() - elapsedTimeStart));
    }
    break;

and I see the Android write all the descriptors available to write.

But the Android enables the service changed on the first connection. Its the second connection where the attempt to send the service changed indication fails. So I believe this has to be some kind of configuration issue as it is very clear the Android is enabling the service changed. So

Either I am not saving and restoring the CCCDs correctly between the first run and the second run, or I am trying to invoke the service changed at the wrong time on the reconnect or I have to wait until the Android enables the service changed again (which it won't do since it has already done it ... unless I do it separately. The latter can't be the case since that violates the spec. So am I saving/restoring wrong?

When the first run disconnects, I invoke the following to get the CCCD data

sd_ble_gatts_sys_attr_get(m_adapter, p_ble_evt->evt.gap_evt.conn_handle, NULL, &saveDataLength, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS);
if(saveDataLength > 0)
{ 
    saveDataBuffer = calloc(1, saveDataLength * sizeof(uint8_t));
    err_code = sd_ble_gatts_sys_attr_get(m_adapter, p_ble_evt->evt.gap_evt.conn_handle, saveDataBuffer, &saveDataLength, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS);
    if (err_code != NRF_SUCCESS)
    {
        printf("Failed getting persistent sys attr info. Error code: 0x%02X\n", err_code);
        fflush(stdout);
    }
}

And on program close I save the 'saveDataBuffer' to a file.

On restart of the application I read 'saveDataBuffer' from the file and in the connection event callback I invoke this code

if (saveDataBuffer != NULL)
{
    err_code = sd_ble_gatts_sys_attr_set(m_adapter, p_ble_evt->evt.gap_evt.conn_handle, saveDataBuffer,
        saveDataLength, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS);
    if (err_code != NRF_SUCCESS)
    {
        printf("Failed updating persistent sys attr info. Error code: 0x%02X\n", err_code);
        fflush(stdout);
    }
}

I have looked at what is in saveDataBuffer both going out and coming in and its only 8 bytes in length so as far as I can tell its the service changed CCCD info.

At this point I call the service changed right after I restore the CCCDs; thus in the connection event. I waited until after encryption but I got the same result of service attributes missing.

RE: I give up; how do I do a service changed?

Hung Bui — Fri, 08 Nov 2019 08:23:27 GMT

I did use Android and it works with other devices => no this doesn't guarantee that the phone has written to CCCD before your call.

It's much easier to test when you have full control of the central device. Please use the nRFConnect on PC to continue.

To get the system attribute you call sd_ble_gatts_sys_attr_get(). And when the bonded connection is reestablished, you call sd_ble_gatts_sys_attr_set() with the exact same data.

You don't need to know which handle the service changed handle is.

We have code to find the service changed cccd handle value in service_changed_cccd() in gatt_cache_manager.c . But it only used to check if the service changed actually exist or not.

Please have a look inside service_changed_send_in_evt() to see how we handle the error codes when calling sd_ble_gatts_service_changed()

RE: I give up; how do I do a service changed?

brianreinhold — Wed, 06 Nov 2019 09:14:09 GMT

Yes I have (I did use Android and it works with other devices). If I knew the handle value of the service changed characteristic I should be able to catch it in my peripheral code ... unless Nordic doesn't pass that one up to the application (like it does other notification/indication attempts).

I trapped all attempts by collector to enable characteristics and I see this

Client Enabling CCCD of characeteristic handle 13 with value 2 at time 1953

However, on a reconnect when I attempt to do a service changed indication I get this:

Started advertising at time 0
Connected at time 234, connection handle 0x0001
Failed invoking service changed indication. Invalid handle 0
Failed invoking service changed indication. Invalid handle 1
Failed invoking service changed indication. Invalid handle 2
Failed invoking service changed indication. Invalid handle 3
Failed invoking service changed indication. Invalid handle 4
Failed invoking service changed indication. Invalid handle 5
Failed invoking service changed indication. Invalid handle 6
Failed invoking service changed indication. Invalid handle 7
Failed invoking service changed indication. Invalid handle 8
Failed invoking service changed indication. Invalid handle 9
Failed invoking service changed indication. Invalid handle 10
Failed invoking service changed indication. Invalid handle 11
Failed invoking service changed indication. Invalid handle 12
Failed invoking service changed indication. Invalid handle 13
Failed invoking service changed indication. Service attributes missing
Result of sending encryption params 0
Security settings reported at time 843:
security level: 2
security mode: 1
key length: 16
Disconnected at time 1078

Of course the Android central is going to fail now as it will try to write to handles based upon the old service tables as it never re-did service discovery to find out that there is no DIS anymore and the HeartRate service values have changed.

RE: I give up; how do I do a service changed?

Hung Bui — Wed, 06 Nov 2019 09:04:16 GMT

Have you enabled indication from the central side ? Please use nRFConnect to test first, before using Android.

RE: I give up; how do I do a service changed?

brianreinhold — Tue, 05 Nov 2019 14:24:45 GMT

Then I better start from 0 and not what I get from the 'get' method. I am still suspicious that it has something to do with the fact I cannot restore the system attributes because I do not get signaled the ..._SYS_ATTR_MISSING event

Since my \examples\connectivity\ble_connectivity does not have the code you reference above, I am kind of stuck with trial and error from zero ... if it even works.

I definitely will not hard code, as I am implementing a peripheral, running it, disconnecting, and then implementing another, one after the other. So far it all works except for the service changed and the BLE_GATTS_EVT_SYS_ATTR_MISSING event. However, my central always re-enables indications and notifications because of the misbehaving devices that do not do bonding correctly.

Doing the 'cycle' starting with 0 I no longer get the invalid handle, instead I get

BLE_ERROR_GATTS_SYS_ATTR_MISSING

RE: I give up; how do I do a service changed?

Hung Bui — Tue, 05 Nov 2019 13:55:06 GMT

Could you try follow our code in gscm_service_changed_ind_send () in gatts_cache_manager ?

do
    {
        err_code = sd_ble_gatts_service_changed(conn_handle, start_handle, end_handle);
        if (err_code == BLE_ERROR_INVALID_ATTR_HANDLE)
        {
            start_handle += 1;
        }
    } while (err_code == BLE_ERROR_INVALID_ATTR_HANDLE);

I'm not 100% sure why we need to do the "trial and error" method like this, may need to check with the developer. But you don't need to do this all the time, if you find the value you can hardcode it I believe.

RE: I give up; how do I do a service changed?

brianreinhold — Tue, 05 Nov 2019 12:53:32 GMT

The 'get' function gives me a value of 0xD.

So I tried both 0 and the value provided by the table from the 'get()' method.. Both gave me the same error 0x3003

'INVALID ATTRIBUTE HANDLE'

There must be something more missing. For example, the restoration of the of the 'system attributes' from the previous connection. However that doesn't happen because I never get a

BLE_GATTS_EVT_SYS_ATTR_MISSING

event. So maybe that's the problem.

RE: I give up; how do I do a service changed?

Hung Bui — Tue, 05 Nov 2019 11:49:14 GMT

Have you really looked into the examples we provide?

You can find in function gscm_service_changed_ind_send() we use sd_ble_gatts_initial_user_handle_get() to get the start_handle for the sd_ble_gatts_service_changed() call (you can also use 0 AFAIK)

The handle of the service change characteristic is not related to the start_handle. You only need the handle of service changed characteristic on the client side. This I assume is handled by the Android phone.

RE: I give up; how do I do a service changed?

brianreinhold — Mon, 04 Nov 2019 22:47:21 GMT

The bottom line is I need the handle of the Service Changed characteristic on the nrf52380 dongle. There are no sp_* APIs in the pc-ble-driver to obtain that value.

I need to invoke the method

sd_ble_gatts_service_changed(adapter_t *adapter, uint16_t conn_handle, uint16_t start_handle, uint16_t end_handle));

and I need the start handle. I use the 0xFFFF for the end handle.

Some help with these

uint8_t* p_sys_attr_data;
uint16_t p_len = 0;
sd_ble_gatts_sys_attr_get(m_adapter, m_connection_handle, NULL, &p_len, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS);
p_sys_attr_data = calloc(1, p_len);
sd_ble_gatts_sys_attr_get(m_adapter, m_connection_handle, p_sys_attr_data, &p_len, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS);
sd_ble_gatts_sys_attr_set(m_adapter, m_connection_handle, p_sys_attr_data, p_len, BLE_GATTS_SYS_ATTR_FLAG_SYS_SRVCS);

would also be nice. The table generated is kind of useless as it has no UUID so you have no idea what attribute it is talking about. The docs say to use this method to get the start handle in the service changed call. Arrg.

I already asked what a system attribute was. After seeing the table I am more confused. Why is there only one entry? Does this table contain only descriptors? None of this makes too much sense, but somebody must know the relation between the handles and UUIDs!

RE: I give up; how do I do a service changed?

Hung Bui — Mon, 04 Nov 2019 16:42:41 GMT

Please correct me if I'm wrong. You are implementing the peripheral on the pc-ble-driver ? And on this you have the GATT server ?

I would suggest to use nRF Connect on PC (you would need one extra dongle/dk) to do service discovery on the device and check if the service changed characteristic is available in the GATT server. You can try to write to the CCCD to enable indication.

Note that Android won't enable indication of service changed characteristic if there is no bond. When there is no bond, the client is not expected to store the service discovery database.

I haven't tried myself but if you don't see the service changed characteristic in the GATT table, you most likely need to enable in the nRF52 code which is at this folder: \examples\connectivity\ble_connectivity

RE: I give up; how do I do a service changed?

brianreinhold — Mon, 04 Nov 2019 14:29:18 GMT

Thanks for the response. I understand that a client can support services; its just in practice (out in the field) I have never seen it ... except perhaps for a CTS.

In any case, I am using the pc-ble-driver so I must use sd_* calls myself. Even so, it looks like it should be easy. Basically, as far as I can tell the GATT service is already set up and the service changed characteristic exists. Now I have an Android application that will attempt to enable indications on the service changed characteristic if it finds one. It works fine for peripheral devices out in the field.

I also have no sd_* APIs in the pc-ble-driver that allow me to get the handle of the GATT services, characteristics, or descriptors. Looked for answers on that, too. I did see some post which suggests the handle is 0x0B but that may even be another platform, so I don't know if that is even right. Found no documentation on it though.

So that's where I am at. What config step am I missing? Where can I find documentation on how to do this?

UPDATE: It appears the handle I am using 0x0B for the Service Changed characteristic is wrong.

The sd_ble_gatts_service_changed() method returns the error incorrect handle. But I cannot get the handle.

RE: I give up; how do I do a service changed?

Hung Bui — Mon, 04 Nov 2019 13:43:50 GMT

Hi Brian,

We have two examples in the SDK : ble_app_gatts_c and ble_app_gatts. Have you tried to test them ?

They are not exactly the same as you wanted (server on peripheral and client on central) however, you can use them as the referral.

Basically, on the server, you need to enable service changed, and send the indication. This is already handled by gatt_cache_manager.c and you just need to call pm_local_database_has_changed() to send the indication. ( it's inside bsp_event_handler() in ble_app_gatts)

On the client, you need to do service discovery and write to the CCCD to enable indication. This is already handled by nrf_ble_gatts.c and the ble_db_discovery.c modules. Please have a look in gatts_evt_handler in main.c in ble_app_gatts_c.