Change in osmocom-bb[master]: trxcon/scheduler: align Downlink reception to the first burst

[fixeria]

Hello laforge, Jenkins Builder, 

I'd like you to reexamine a change. Please visit

    https://gerrit.osmocom.org/c/osmocom-bb/+/17354

to look at the new patch set (#3).

Change subject: trxcon/scheduler: align Downlink reception to the first burst
......................................................................

trxcon/scheduler: align Downlink reception to the first burst

It may happen that the burst reception would start from bid != 0:

  <0005> sched_trx.c:263 (Re)configure TDMA timeslot #2 as TCH/H+SACCH
  <0005> sched_trx.c:420 Activating lchan=TCH/H(0) on ts=2
  <0005> sched_trx.c:420 Activating lchan=SACCH/TH(0) on ts=2
  <0006> sched_lchan_xcch.c:96 Received incomplete data frame at fn=0 (0/104) for SACCH/TH(0)
  <0006> sched_lchan_xcch.c:106 Received bad data frame at fn=0 (0/104) for SACCH/TH(0)

so in that case, both measurement processing and the frame number
calculation would yield incorrect and/or incomplete results. The
Rx burst mask can be used to eliminate this problem.

In particular, if we shift it left instead of cleaning, it would
never be equal 0x00 after at least one burst is received. This
would allow us to skip decoding of an incomplete frame at the
beginning when the logical channel was just activated.

Note that TCH/H handler is not affected because it already uses
the strategy described above, so we keep it unchanged.

Change-Id: Ib8ddf2edd5ef84f2ab12155f7a8874c9fc56d436
Related: OS#3554
---
M src/host/trxcon/sched_lchan_pdtch.c
M src/host/trxcon/sched_lchan_tchf.c
M src/host/trxcon/sched_lchan_xcch.c
3 files changed, 18 insertions(+), 9 deletions(-)


  git pull ssh://gerrit.osmocom.org:29418/osmocom-bb refs/changes/54/17354/3
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Gerrit-Project: osmocom-bb
Gerrit-Branch: master
Gerrit-Change-Id: Ib8ddf2edd5ef84f2ab12155f7a8874c9fc56d436
Gerrit-Change-Number: 17354
Gerrit-PatchSet: 3
Gerrit-Owner: fixeria <axilirator at gmail.com>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-MessageType: newpatchset
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