Szymon -
On Wed, 15 Feb 2012, Mat Martineau wrote:
Szymon -
On Wed, 15 Feb 2012, Szymon Janc wrote:
Hi Szymon,
Hi Gustavo,
I was pretty sure this patch will trigger some comments :-)
+ /* drop frame without F-bit set when in WAIT_F state */
+ if (test_bit(CONN_WAIT_F, &chan->conn_state) &&
+ !__is_ctrl_final(chan, control))
+ goto drop;
+
I think this is wrong, you are completely dropping frames here while you
should at least process the reqseq received. Check the spec, the WAIT_F
table.
Another point is that the WAIT_F state belongs belongs to the transmit
side,
and you are checking for it in the receive side. This also seems wrong to
me.
Spec is a bit unclear here for me, so this is how I understand it:
Transmitter state machine is triggered by events from receiver state
machine.
For receiver to take action (and sent event to tx machine eventually)
condition
must be fulfilled. Every event in receiver state machine which can possibly
trigger tx machine has 'With-Valid-F-bit' condition (so my understanding is
that
if Fbit has invalid value action should not be triggered, and next matching
event should be check, here last one - 'Recv frame' which has action
'Ignore').
So if transmitter is in WAIT_F state any frame received without Fbit=1
doesn't
fulfill 'With-Valid-F-bit' condition and should be dropped.
My opinion is that spec is redundant here since if 'With-Valid-F-bit' is
not
valid rx machine will never emit 'Recv ReqSeqAndFbit' with F=0 when tx is
in
WAIT_F and that condition will never happen (yet, it is described in WAIT_F
state table).
I agree with Gustavo, this code is incorrect.
"With-Valid-F-bit" only means that both the P-bit and F-bit are *not* set.
The packet should be dropped when P=1 and F=1, but your check only looks at
the TX state and F-bit.
Frames without the F-bit need to be processed, because the remote device may
have sent a frame with the F-bit that did not reach us.
I saw your question on IRC, so I thought I would clarify.
The definition of "With-Valid-F-bit is on page 167 of the 4.0 spec,
and is very narrow. The ONLY time an F-bit is invalid is when it is
set and the P-bit is also set. Every incoming frame with F=0 meets
the With-Valid-F-bit condition and should be passed to the TX state
machine.
The WAIT_F state machine in the spec explicitly mentions receiving
frames with F=0 because those frames are *expected*. An F=1 frame
could have been lost and the remote side might think it's ok to send
other frames. There are parts of the RX state machine that look for
PbitOutstanding - which is exactly this situation.
Your PTS results show PTS saying that control bits were not set
correctly on the first retransmitted iframe, but the control fields
look valid to me. Does your version of PTS allow both of the current
alternatives from TP/ERM/BI-05-C (reqseq=1 or reqseq=0) in the
retransmitted frames?
Also I never find problem to pass this test in PTS with the following
l2test
line:
l2test -P 17 -X 3 -b 48 -w -D 1 -N 2
Please tell the problem you have in PTS so we can try to find a better
solution for this.
We tried with l2test -x -X ertm -P 33 -N 2 (I guess -x vs -w is not
relevant here).
I'm bit surprise how you pass that test if receiving of REJ (P=0, F=0)
triggers
retransmission I-Frames before I-Frame with F=1 was sent by PTS (and this
is
what PTS didn't like saying it received unexpected I-Frame). So now we have
test
failed although we did retransmitted I-Frame only once (but before frame
with
Fbit=1 was received).
Some discussion about that can be found here as well:
https://www.bluetooth.org/pts/issues/view_issue.cfm?id=8413
https://www.bluetooth.org/tse/errata_view.cfm?errata_id=4512
BTW, we use following PTS version:
PTS v. 4.4.2.8
L2CAP v. 7.4.0.1
--
Mat Martineau
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
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