Discovery DIS

[anSolo]

Hello,

I use nrf52840-dk as central_hr and nrf52833-dk as peripheral_hr, examples from NRF Connect SDK.

It works well, but I want to implement reading Device Information like Model Number String on my central device.

I can read it on my phone, using nRF Connect, so peripheral device is ok

So, what I did:

1. Added CONFIG_BT_GATT_DM=y to prj.conf to use Discovery manager

2.Added CONFIG_HEAP_MEM_POOL_SIZE=2048 to prj.conf, because Discovery manager uses k_malloc

3.I call 

err = bt_gatt_dm_start(conn, BT_UUID_DIS, &discovery_cb, NULL);

when connected, and I get into discovery_completed_cb, but I don't understand how to check if Model Number String or Manufacturer Number String exists,

how to check could I read it, write or notify and how to read the value.

Comparing to central_bas example, they use functions like bt_bas_notify_supported(&bas),

and they have special structure for BAS 

static struct bt_bas_client bas;

I didn't find something like this for DIS.

Thank you,

Anton

[Hung Bui]

Hi anSolo, 
I haven't tried on my own to discover and read DIS characteristic, but you can refer to the bt_bas_handles_assign to do something similar. 

So you need to make a similar function and instead of assign the BAS service , you call 
if (bt_uuid_cmp(gatt_service->uuid, BT_UUID_DIS)) {

After that you need to look for the characteristics inside the DIS service, for BAS it's handled in bt_bas_handles_assign()

So instead of bt_gatt_dm_char_by_uuid(dm, BT_UUID_BAS_BATTERY_LEVEL); you can call bt_gatt_dm_char_by_uuid(dm, BT_UUID_DIS_MODEL_NUMBER); After that you need to get the characteristic handle using bt_gatt_dm_desc_by_uuid()

After you get the characteristic handle, you can do a read of the characteristic using bt_gatt_read(). Note that the DIS service doesn't support notification, so unlike the BAS service, you don't enable notification, you do a read instead. 

[anSolo]

Thank you,

I tried it and it works!

I have question about bt_gatt_read().

dis->read_params.func = gatt_read_cb;
dis->read_params.handle_count  = 2;
dis->read_params.handles = dis_handles;
err = bt_gatt_read(dis->conn, &(dis->read_params));

I read two values,

BT_UUID_DIS_MODEL_NUMBER, which is "Model"

and BT_UUID_DIS_SERIAL_NUMBER, with value "serial"

Here you can see part of my log,

gatt read cb

data length 11

data = Modelserial

gatt read cb

data length 0

empty data

1)Is it OK that I get common length for two values, and values are not separated?

How could I split them?

2)Is it OK that I get extra callback with zero length?

[Simon]

I took a brief look at it yesterday, but I would need some more time to understand this. 

One option is to run bt_gatt_read with a single handle two times.

You could also take a look at zephyr/subsys/bluetooth/shell/gatt.c

[anSolo]

I do the same as in the example you provide,

Maybe I didn't describe it correctly,

the problem is that in multiply read I get one callback and one length for all values,
and I don't understand how to split it, and what value for what characteristic is.

[Simon]

I'm able to reproduce it. I'm not sure how to go about this, so I have forwarded the question internally. I will keep you updated.

Best regards,

Simon

[Simon]

It seems like most of the developers are on vacation. Can you forward the question to any of these places: Zephyr - Asking for help.

If you find a solution, would you be able to share it here, so other people can benefit?

However, I think a workaound is to run bt_gatt_read() two times, with dis->read_params.handle_count  = 1;

[anSolo]

I've created message on zephyr mailing list

I write here, If any updates

Thank you for the help!

Please, keep me updated If nordic developers find a solution.