DLT for Bluetooth Baseband (was DLT for Bluetooth Low Energy)

[Dominic Spill <dominicgs () gmail com>]

On Thu, Jun 13, 2013, Guy Harris wrote:
> On Jun 13, 2013, at 12:52 PM, "dragorn" <dragorn <at> kismetwireless.net> wrote:
> > Got another request - can we get one for _BLUETOOTH_BB as well, for
> > standard bluetooth baseband data?  Spec is at :
> >
> > https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=229737
> > Baseband is at page 354
>
> Those fields don't end on octet boundaries; are the bits stuffed into octets disregarding octet boundaries?

We respect octet boundaries for fields of 8 bits or fewer, although
that means that we sometimes pad fields.  For example, the packet
header is 10 bits followed by an 8 bit checksum.  We use three octets
to hold the data: first containing lt_addr and type, second containing
the flags and the final octet contains the checksum.

This means that there is a single bit of padding in the first octet
and 5 bits in the second.

> The spec says that "data fields generated internally at baseband level, such as the packet header fields
> and payload header length, shall be transmitted with the LSB first"; are the bits stored in octets as
> they're received and, if so, is the first bit of the packet the MSB or the LSB of the first bit?
> Or are the packets not presented in quite as raw a fashion?

They aren't that raw.  We pull out all of the fields and convert them
from air order to host order before writing the packet out, including
the payload, so the first bit will be the MSB of the first byte.  The
syncword is trimmed from the packet in the current version, although
this will probably change once we stop encapsulating the packets in an
ethernet type, something we did in the past to deliver the packets to
Wireshark.

There is also a packet meta data header prepended to include fields
that are not carried within the paket, such as channel, direction and
clock.

I'm sorry to have left this for a month, I wasn't subscribed to the
list when the messages were sent so I had missed it.  Please let me
know if this raises any more questions.

Thanks,
  Dominic
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