Re: [Bluez-users] Detecting RSSI without connecting

[Scott W Gifford <gifford@umich.edu>]

Marcel Holtmann <marcel@holtmann.org> writes:

> Hi Scott,
>
>> For a project I'm working on, I'd like to determine which of several
>> (possibly many) Bluetooth devices is closest.  "Best RSSI" is a good
>> enough approximation of "closest" for my purposes, and since there may
>> be many devices and I don't have any other interest in them, I'd like
>> to get the RSSI without establishing a connection with each device.
>> 
>> It appears that "hcitool rssi <bdaddr>" requires that a connection is
>> established.  Do any cards provide a way of getting RSSI that doesn't
>> require establishing a connection?
>
> starting with the Bluetooth 1.2 specification it is possible to get the
> RSSI value from the inquiry results. Check the mailing list archives for
> more details.

Thanks Marcel,

I bought a Bluetooth 1.2 adapter (an IOGear GBU211), but it still
doesn't seem to work.  From what I found in the archives and the
source code, it looks like I should set the inquiry mode to 1, then
just use "hcitool scan".  But it looks like the inquiry mode doesn't
get set properly:

  [root@gifford tools]# /usr/local/sbin/hcidump -X &
    [1] 10382
    HCIDump - HCI packet analyzer ver 1.12
    device: hci0 snap_len: 1028 filter: 0xffffffff
  [root@gifford tools]# /usr/local/sbin/hciconfig hci0 inqmode
    < HCI Command: Read Inquiry Mode (0x03|0x0044) plen 0
    > HCI Event: Command Complete (0x0e) plen 4
      0000: 01 44 0c 11                                       .D..
    Read inquiry mode on hci0 returned status 17
  [root@gifford tools]# /usr/local/sbin/hciconfig hci0 inqmode 1
    < HCI Command: Write Inquiry Mode (0x03|0x0045) plen 1
      0000: 01                                                .
    > HCI Event: Command Complete (0x0e) plen 4
      0000: 01 45 0c 11                                       .E..
  [root@gifford tools]# /usr/local/sbin/hciconfig hci0 inqmode
    < HCI Command: Read Inquiry Mode (0x03|0x0044) plen 0
    > HCI Event: Command Complete (0x0e) plen 4
      0000: 01 44 0c 11                                       .D..
    Read inquiry mode on hci0 returned status 17
  [root@gifford tools]# hcitool inq
    Inquiring ...
    < HCI Command: Inquiry (0x01|0x0001) plen 5
      0000: 33 8b 9e 08 64                                    3...d
    > HCI Event: Command Status (0x0f) plen 4
      0000: 00 01 01 04                                       ....
    > HCI Event: Inquiry Result (0x02) plen 15
      0000: 01 a5 2b 19 17 00 08 01  00 00 10 01 32 6a 78     ..+.........2jx
    > HCI Event: Inquiry Result (0x02) plen 15
      0000: 01 a5 2b 19 17 00 08 01  00 00 10 01 32 6a 78     ..+.........2jx
    > HCI Event: Inquiry Complete (0x01) plen 1
      0000: 00                                                .
        08:00:17:19:2B:A5       clock offset: 0x786a    class: 0x320110

It looks like read and write are both returning 17 (hex 0x11), which
seems to mean unsupported.  hciconfig -a says:

    hci0:   Type: USB
        BD Address: 00:02:72:C0:08:CB ACL MTU: 377:10  SCO MTU: 16:0
        UP RUNNING PSCAN ISCAN
        RX bytes:3340 acl:0 sco:0 events:135 errors:0
        TX bytes:728 acl:0 sco:0 commands:87 errors:0
        Features: 0xff 0xff 0x0d 0x38 0x00 0x00 0x00 0x00
        Packet type: DM1 DM3 DM5 DH1 DH3 DH5 HV1 HV2 HV3
        Link policy: RSWITCH HOLD SNIFF PARK
        Link mode: SLAVE ACCEPT
        Name: 'BlueZ (0)'
        Class: 0x000100
        Service Classes: Unspecified
        Device Class: Computer, Uncategorized
        HCI Ver: 1.2 (0x2) HCI Rev: 0x69 LMP Ver: 1.2 (0x2) LMP
        Subver: 0x694a
        Manufacturer: Broadcom Corporation (15)

Am I doing this wrong, or is it possible that a Bluetooth 1.2 device
doesn't support RSSI on inquiry?  If this device doesn't support it,
can anybody recommend a device available in the US that does support
RSSI on inquiry?  Does the feature need to be supported on both the
inquiring device and the inquired device to get RSSI information, or
is support on the inquiring device enough?

Thanks!

----ScottG.


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