Re: gatt advertising

Hi Anderson,

anderson.lizardo@openbossa.org writes:

First of all, thank you for your extremely helpful reply!

On Tue, Jul 30, 2013 at 9:08 AM, Dirk-Jan Binnema [off-list ref] wrote:

quoted

Hi all,

First of all, BlueZ (and the Linux kernel) does not support the
"Peripheral" role fully yet, which is what you want here.

Therefore, you need to do a few things by hand.

quoted

- Is any extra step is needed to advertise the service beyond
  gatt_service_add and 'hciconfig leadv'?

You need to manually add the UUIDs on the LE advertising data. For
this, currently you need to send the "LE Set Advertising Data" HCI
command manually to the controller (e.g. using "hcitool cmd"). See the
Core Spec page 1062 for the HCI command format, and Section 11
"Advertising and Scan Response Data Format (page 1735), and Appendix C
"EIR and AD Formats" (page 1762) for the Advertising Data format
specifically.

Yes, this seems to work. For other people trying the same:

hcitool -i hci0 cmd 0x08 0x0008 12 11 07 xx xx xx xx xx xx xx xx \
       xx xx xx xx xx xx xx xx 00 00 00 00 00 00 00 00 00 00 00 00 00

will do the advertisement when using a 128-bit UUID (the xx part,
'MY_SERVICE_ID') -- and importantly, this needs to be encoded, basically
the bytes you get from the following:

    bt_string_to_uuid (&srv_uuid, MY_SERVICE_UUID);
    for (u = 0; u != 16; ++u)
         printf ("%x ", ((uint8_t*)&srv_uuid.value)[u]);


For 16-bit UUIDs, you need to change the length bytes (the 12 and 11),
see the docs above for the details.

quoted

  (It seems that neither mine, nor any of the other services (proximity,
  time, alert, ...) are recognized until after I connect(*). After
  connection, I can see all of them.

They are only visible after connection probably because iPhone
triggers a Service discovery when BlueZ connects to it.

quoted

- It also seems the device stops advertising after a while -- is there
  some way to programmatically put it in advertising mode (like
  hciconfig leadv) and keep it that way?

Actually, advertising stops as soon as a connection is established.
This is a controller feature, not controllable by BlueZ. You need to
enable advertising again manually.

Okay, that's good to know!

One other thing I've hit upon is that apparently, long-writes/reads are
supported by ATT yet (looking at channel_handler, and seeing some
'Unsupported request 0x16'), although it seems Bluez can do long-writes
itself.

Are there plans to add long-writes/reads to ATT? Or would this be very
easy to add? (I suppose not!).

Thanks,
Dirk.


-- 
Dirk-Jan C. Binnema                  Helsinki, Finland
e:djcb@djcbsoftware.nl           w:www.djcbsoftware.nl
pgp: D09C E664 897D 7D39 5047 A178 E96A C7A1 017D DA3C

On Tue, Jul 30, 2013 at 8:03 AM, Anderson Lizardo
[off-list ref] wrote:

Hi Dirk,

On Tue, Jul 30, 2013 at 9:08 AM, Dirk-Jan Binnema [off-list ref] wrote:

quoted

Hi all,

I'm trying to build a GATT-based service that exposes some
characteristics that can be accessed by clients; I'm using
gatt_add_service_add for that, and the BLExplr app on the iPhone side.

The good news is that it seems to be possibly to do so :-) (I'm using
git master + the 128-bit uuid patch I wrote); however, it seems the
service is not advertised; I need to connect to the device first before
I can see it; at least when trying with an iPhone.

First of all, BlueZ (and the Linux kernel) does not support the
"Peripheral" role fully yet, which is what you want here.

Therefore, you need to do a few things by hand.

quoted

- Is any extra step is needed to advertise the service beyond
  gatt_service_add and 'hciconfig leadv'?

You need to manually add the UUIDs on the LE advertising data. For
this, currently you need to send the "LE Set Advertising Data" HCI
command manually to the controller (e.g. using "hcitool cmd"). See the
Core Spec page 1062 for the HCI command format, and Section 11
"Advertising and Scan Response Data Format (page 1735), and Appendix C
"EIR and AD Formats" (page 1762) for the Advertising Data format
specifically.

quoted

  (It seems that neither mine, nor any of the other services (proximity,
  time, alert, ...) are recognized until after I connect(*). After
  connection, I can see all of them.

They are only visible after connection probably because iPhone
triggers a Service discovery when BlueZ connects to it.

quoted

- It also seems the device stops advertising after a while -- is there
  some way to programmatically put it in advertising mode (like
  hciconfig leadv) and keep it that way?

Actually, advertising stops as soon as a connection is established.
This is a controller feature, not controllable by BlueZ. You need to
enable advertising again manually.

Note that most controllers on the market (if not all of them) obey the
LE topology, so when they are slave in a connection, they will
probably not be able to send connectable advertisements. You will only
be able to enable advertising again once the link is disconnected.

quoted

- Should the UUID of the service be part of the UUIDs property in
  org.Bluez.Adapter1 and org.bluez.Device1? (I tried 'btmgmt aad-uuid
  <uuid> 0' and then then <uuid> becomes visible in the
  org.bluez.Device1 UUIDs, but sadly, the iPhone still doesn't seem to
  see it, pre-connection).

As BlueZ does not support peripheral role yet, the D-Bus API does not
have any effect on this situation.

quoted

(*) but for some reason, in the aforementioned app, I can see the 'Tx Power
Level' value before connection.

This app is most likely reading the TX Power value which is inserted
on the LE Advertising Data by the kernel. BlueZ does not have a
working TX Power service yet.

Best Regards,
--
Anderson Lizardo
Instituto Nokia de Tecnologia - INdT
Manaus - Brazil