libosmo-abisrecently marked the 'out_cb' of the subchan_demux
as 'const', which caused compiler warnings/errors.
Related: libosmo-abis.git Ia082b9fddf03d02afd007825a1588a3ef0dbedae
Change-Id: I0cf430980e50fa8094f0efc7642004fb5923c4c6
Finally the bit ordering and bit format of the SuperChannel has been
figured out.
* the data as read from DAHDI must be flipped (0->1 / 1->0). why?
* the data must be read lsb-first when converting into a bit-buffer
We are now getting the following output e.g. for a OM2000 "TX
Configuration Request" message:
fa 03 8a 8a 80 80 00 13 00 b0 0b 00 ff 01 20 00 2e 2b 1c 00 06 01 95 81 76 00 e9 bf
^ lapd hdr ^ OML ^l ^OM2000 TX Config Req for 43 dBm
In the super channel mode, it seems the BTS transmits one byte in each
timeslot, accross the entire link.
This basically means that if you have a 10 byte long signalling message
to be sent, its first byte will be in TS1 up until the tenth byte in
TS10.
As we are reading in 160 byte chunks from the E1 timeslots, we build a
matrix with 160 columns (for each byte) and 24/30 rows (timeslots). So
we write 24 times 160 bytes into the matrix.
Once we have completed all timeslots, we start to read the matrix by
reading byte 0 of each timeslot (in incrementing TS order), next byte 1
of each timeslot, ... until we end up having read 160 times 24 bytes
from the matrix.
The resulting bitstream needs to be HDLC-synchronized and the resulting
messages passed up for further decoding.
Harald Welte