[Bluez-devel] externally monitoring uart HCI data with the use of hcidump

[Ruud Beukema <ruudbeukema@gmail.com>]

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Hi,

I'm writing a HCI monitoring program which is able to capture HCI
traffic between a BlueCore and a Host independent from the BlueZ stack.
The program's output is a log of all HCI traffic in a format that can be
reread and interpret using the hcidump --read-dump=hcidumplog

The reaction on an earlier mail from my colleague (Han Hoekstra) didn't
solve the problem unfortunately, so I'll try to reformulate our problem
in more detail hoping you can help us out.

We're able to extract the BCSP packet from the SLIP layer. We're also
able to derive the HCI packet from the BCSP packet. But then, to put the
HCI packet in a hcidump usable format, a HCIDUMP HEADER must be put in
front of the HCI packet. This is where a first question is about.
According to the hcidump source code the HCI packet's header is a 12
byte header containing
    -    HCI packet length (2 byte)
    -    HCI packet direction (1 byte)
    -    HCI packet pad (1 byte)
    -    HCI timestamp seconds (4 byte)
    -    HCI timestamp microseconds (4 byte)

What's the pad byte's function/value?

Now the second question. When I retrieve a HCI packet and put a HCIDUMP
HEADER in front of it, it is not re-readable using hcidump. According to
the hci_dump function in hci.c (line: 2666) the first databyte of the
frame data holds the packet type which forms the starting point of the
interpretation of the HCI packet in hcidump. This packet type byte is an
extra byte not present in the real communication, but necessary for
hcidump to work properly. I can find the defines for the different
packet types (bluetooth/hci.h) but I can't figure out where and how this
byte is calculated or given a value. I first thought this byte was given
a value depending on the contents of the BCSP packet header, but I can
find no relationship between the two to be honest. (Maybe due to seeing
too much HEX code the last few days). So the question here is:

How to calculate the packet type byte between the HCIDUMP HEADER and the
original HCI packet?

I'd really appreciate your help!

Regards

Ruud

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