nRF Connect (Desktop) reports 'Received a Gatt timeout'

[Remco Poelstra]

Hi,

I working on a BLE app with 2 custom services.

When I try to expand a characteristic I get a spinning indicator below the characteristic and after a while I get a 'Received a Gatt timeout'.

If instead I just try to write to a characteristic I immediately get a 'Characteristic value write failed: A gatt operation already in progress with device id xxxx.'

In my BLE event handler I only see the following events:

BLE Event: BLE_GAP_EVT_CONNECTED (0x0010).
BLE Event: BLE_GATTC_EVT_EXCHANGE_MTU_RSP (0x003A).
BLE Event: BLE_GAP_EVT_DATA_LENGTH_UPDATE_REQUEST (0x0023).
BLE Event: BLE_GAP_EVT_DATA_LENGTH_UPDATE (0x0024).
BLE Event: BLE_GATTS_EVT_SYS_ATTR_MISSING (0x0052).
BLE Event: BLE_GAP_EVT_CONN_PARAM_UPDATE (0x0012).

I do not see any events in the GATT event handler.

How do I find out what is going wrong? I'm totally lost here.

I'm using an nRF52840 with SDK 15.0.0.

Thanks in advance.

Kind regards,

Remco Poelstra

[kmassa5]

Hey Remco,

I seem to be having the same issue described in your post and was wondering if you could provide more info on how you called sd_ble_gatts_sys_attr_set() to fix your problem!

Thanks!

[Remco Poelstra]

Hi,

In your BLE event handler I call it like this:

	case BLE_GATTS_EVT_SYS_ATTR_MISSING: {
	    uint32_t e = sd_ble_gatts_sys_attr_set(
		event->evt.gap_evt.conn_handle,
		/* p_sys_attr_data: */ NULL,
		/* len: */ 0,
		/* flags: */ 0);

[wpreska1]

Thanks for posting this Remco, and thank you for figuring this out!

Can you (or anyone?) please direct us to where this is explained? 

Your solution solved the problem.  But how could we developers know to put this case statement in our code?  Where is this documented?  You would think it would be in the examples... (I didn't look in all of them, but it's not in the peripheral template example project, nor several others).

I'm just left wondering how we were supposed to know about this?

[Remco Poelstra]

These are difficult problems indeed. I don't know where they are documented, but in this case the hint was in the list of events (in my first post). I presumably double checked them and for each event tried to see whether a response was necessary but missing.

A lot of trial and error is involved here.

[Kenneth]

Good question, not an easy answer. 

Typically events are handled by a software module of some sort (pm_init(), gatt_init()...), however likely some of the "simpler" BLE peripheral examples (e.g. template or examples that do not support bonding) may not handle them all by default. Fyi: pm_init() will init peer manager to handle the BLE_GATTS_EVT_SYS_ATTR_MISSING event in question, this event is required when supporting bonding.

There are message sequence charts charts you may look at if you want to handle these events yourself (not something I would recommend, better to use the software modules): 
https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v7.2.0/group___b_l_e___g_a_p___m_s_c.html

In terms of "feature complete" BLE peripheral example I would suggest the HRS example as an reference.

Kenneth