mesh gatt and ble gatt

[Blastka]

Hi. I have read the documentation and I have a couple of questions:

1. What makes work different mesh_gatt and nrf_ble_gatt? Why can't they work together (maybe it's because of ATT_MTU, but I'm not sure).
2. Why can I write and read a characteristic without function gatt_init in nrf5 sdk?
3. how the characteristics created as in the BLE project in mesh will work? i created service and characteristics. they will communicate through the mesh gatt?

[Hung Bui]

Hi Blastka, 

1. Yes they can work together. In our co-exist example we don't have GATT Proxy implemented but it's possible to add that in. Please have a look at my example here: https://devzone.nordicsemi.com/f/nordic-q-a/53837/including-nrf5-sdk-for-mesh-functionality-in-an-nrf5-sdk-example/235538#235538

2. Could you explain more ? gatt_init () function initialize the nrf_ble_gatt module. It's not directly related to read/write characteristics

3. Mesh Gatt is only handling the Mesh GATT proxy/provisionining service. So it doesn't handle any other service. You handle your service as usual. 

[Blastka]

1. yes, but in your coexistence example gatt_init is commented out. In my example, gatt and mesh gatt do not work together.

2. Why? gatt is responsible for communicating characteristics and services. 

3. another question. I activated pb-gatt and proxy in config, but did not initialize. I use gatt_init. my treatments go to mesh_gatt_on_ble_evt and call hardfault. 
static mesh_gatt_t m_gatt;
NRF_SDH_BLE_OBSERVER (m_gatt_obs, NRF_MESH_GATT_BLE_OBSERVER_PRIO, mesh_gatt_on_ble_evt, & m_gatt);
#endif

[Hung Bui]

1. It's commented out because the mesh_gatt.c already handle the ATT_MTU request. 

2. Again the gatt_init() is only initialize the nrf_ble_gatt module which handles the ATT_MTU and the Data lenght request. It's not related to the service and characteristics.

3. Please send what inside your "gatt_init" maybe it's different from my gatt_init. Please follow what I did in the example that I quoted. Note the change in  nrf_mesh_provisionee.c 

[Blastka]

3.  This is my project. The project has no uart.

NRF_BLE_GATT_DEF(my_m_gatt);

/**@brief Function for initializing the GATT module.
*/
void gatt_init(void)
{

ret_code_t err_code = nrf_ble_gatt_init(&my_m_gatt, NULL);
APP_ERROR_CHECK(err_code);

err_code = nrf_ble_gatt_att_mtu_periph_set(&my_m_gatt, NRF_SDH_BLE_GATT_MAX_MTU_SIZE);
APP_ERROR_CHECK(err_code);
}

Because of observers it works so incorrectly. NRF_BLE_GATT_DEF(my_m_gatt);      and 
NRF_SDH_BLE_OBSERVER (m_gatt_obs, NRF_MESH_GATT_BLE_OBSERVER_PRIO, mesh_gatt_on_ble_evt, & m_gatt);
Why are they processed together. nrf_ble_gatt_on_ble_evt and mesh_gatt_on_ble_evt.

[Hung Bui]

As I mentioned the gatt_init() initialize nrf_ble_gatt () which handle the ATT_MTU update and Data length update. This is already handled by mesh_gatt so you don't need that module.

Please remove the nrf_ble_gatt.h and nrf_ble_gatt.c from your project. 

It has no direct impact to GATT services and characteristics. 

[Blastka]

I deleted, now my program hangs in this place when disconnecting from the phone, when i run  advertising without mesh:
.thumb_func
.weak HardFault_Handler
HardFault_Handler:
b .

[Hung Bui]

Hi, 
Hardfault is not a deadend, please try to debug and find where it crashed. Have a look here: https://devzone.nordicsemi.com/f/nordic-q-a/12291/what-can-cause-a-hardfault-and-how-to-catch-it

Please try to check and compare your code to the coexist example or my example that I pointed to earlier. 

[Blastka]

I tried, in your example you removed advertising, now I don't understand

[Hung Bui]

I removed it because when you enable PB-GATT, the advertising is handled inside a_listen_start() in nrf_mesh_prov_bearer_gatt.c 

Please try to study the mesh stack and get to understand how it work this is needed if you want to customize it and make something differently. 

What you need to know is how the advertising is handled before provisioning (handled by the prov_bearer_gatt and after provisioning it's inside proxy.c . 

In the default coexist we don't have proxy and PB-GATT so that's why it's handled in main.c 

[Blastka]

yes, I studied well about proxy and PB-GATT in documentation. but nowhere is it clearly written that advertising and proxy cannot work together. an example of coexistence, I just got confused. I would be grateful to receive information where you can find out how everything works in libraries. Or is it just to study the program myself?

[Hung Bui]

Hi Blastka,
I afraid you may need to study the code. The point is that to advertise with connectable advertising, the mesh stack would need to use the softdevice to advertise. It's because the mesh stack is not created to handle BLE connection. And the softdevice only allow one advertising set at a time. So you need to combine what you want to advertise with what the mesh stack advertise (either as PB-GATT or Proxy GATT). 
So there are 2 options: 
First option is to remove what mesh is advertising, and only advertise with your own code in advertising_init and advertising_start in main.c 
Second option is to do what I suggested, integrate what you want to advertise into mesh proxy/provisioning advertising. 

The draw back of option1 is that if you don't advertise with correct format of Mesh unprovisioned UUID and Mesh proxy service, the mesh app won't be able recognize the device as a mesh node/proxy.