The band was derived from the ARFCN but this does not work for
PCS1900/DCS1800 due overlapping ARFCNs. Use the already existing
band configuration to select the band for the MphInitReq. The
dsp firmware will complain if the band/arfcn do not match.
This allows us to do RF measurements (EDGE EVM and the like) even
without having any PCU/RLC/MAC code as of now.
To use it, configure PDCH type timeslots (e.g. TS 7) in the BSC and then
use "trx 0 7 activate 0" to manually activate the PDTCH lchan on top
of that timeslot. The BTS will now happily transmit EDGE/8PSK data.
The ciphering parameters in L1 are persistent accross MPH
deactivate/activate, so we need to make sure to always initialize them
cleanly at RSL CHAN ACT time. This has the added benefit that we can
also activate channels that have encryption enabled from the very
beginning (required for encrypted handover).
where previously we would only see
<0006> oml.c:931 (bts=0,trx=0,ts=1,ss=0) MPH-DEACTIVATE.req (FACCH/F)
we now get
<0006> oml.c:931 (bts=0,trx=0,ts=1,ss=0) MPH-DEACTIVATE.req (FACCH/F RxUL)
to notice it is modifying the receive path in the uplink direction.
Send the RSL ACT ACK/NACK after the Layer1 firmware has acked the
activation/deactivation. In case the channel can not be activated
we will send a NACK. In case the channel can not be deactivated we
will send an ACK and the next time the channel is activated we will
send a NACK. The release ack will be sent once the TxDownlink of the
TCH/SDCCH is closed.
Change the rsl_tx_chan_nack method to create a new msgb to be used
by the hardware layer, change the return value to ask the caller to
delete the msgb.
Use the deact_sach (renamed to deact_sacch in master) to remember if the
SACCH has been disabled. This should fix the case of lchan errors due releasing
the lchan twice.
If the deactivation is failing the channel needs to be moved into
and error state, if the deactivation completed the channel needs to
be set to the none state and set the state to release reqeust on
the deactivation.
We now check if the received message is an LAPDm I frame in order to
determine if we have received the first valid encrypted message on the
radio link. This relates to the fact that we often see 'old' UI frames
coming up from L1, even after it has confirmed decryption has been
enabled.
When the RR CIPH MODE CMD is transmitted to the MS, we need to tell the
L1 to enable decryption on RX. After the first received frame has been
decrypted successfully, we will enable encryption also on transmit.
This has been tested with A5/1 so far, but A5/2 and A5/3 should work
exactly identical.
In L1 RTP mode, the L1 already does all the bit-shifting and re-ordering
required for the RTP formats (which have different bit/nibble order than
the ETSI/3GPP encodings, for some odd reason).
We don't enable it by default yet, as only HR/FR/EFR work with it, but
AMR has some yet to be debugged problem.
Enabling USE_L1_RTP_MODE would save some CPU cycles on the ARM side.
If we don't do this on recent L1, the L1 will refuse the open after
re-starting osmo-bts.
There still is an issue in case osmo-bts crashes. We should have a
respawn loop that re-loads the DSP firmware before re-starting osmo-bts,
just to make sure...
We now have to explicitly indicate the tchPlType at channel activation
type, so L1 knows which channel decoder to use (FR, EFR, AMR, ...)
Also, we properly implement the initial codec mode selection as per TS
05.09
Using osmo-bts-sysmo and this code, it is now possible to do FR and AMR
based voice calls on TCH/F.
A lot of CPU is wasted in the conversion between the RTP formats and the
L1 specific formats for the codec frames. All data needs to be shifted
by four bits, and the order of bits needs to be reversed in every byte.
when we activate the SCH in the DSP, we start a 5-second timer. If
we ever do not receive any MPH-TIME.ind primitives from L1 within
that time frame, we stop the process (and will be re-spawned)
The sequence is as follows:
0) start osmo-bts
1) start connection attempts to BTS
2) issue L1-RESET.req
3) receive L1-RESET.conf
4) issue RF-ACTIVATE.req
5) receive RF-ACTIVATE.conf
6) receive attributes for TRX
7) receive opstart for TRX
8) issue MPH-INIT.req
[...]
The important point here is: We don't want the BSC to set TRX attributes or do
TRX opstart before our RF related hardware is initialized.
In SDCCH4, we use lchan number 0...3 for the SDCCH/SACCH, and
we statically use lchan[4] as the dummy for activating the CCCH
L1 SAPIs.
In order to make combined and non-combined CCCH orthogonal, we simply
also use lchan[4] in that case. On a 'pure' CCCH, therefore lchan
0..3 are unused and 4 is the actual CCCH.
This code re-works osmo-bts to add support for the upcoming sysmocom BTS.
It also tries to add some level of abstraction between the generic
part of a BTS (A-bis, RSL, OML, data structures, paging scheduling,
BCCH/AGCH scheduling, etc.) and the actual hardware-specific bits.
The hardware-specific bits are currently only implemented for the sysmocom
femtobts, but should be (re-)added for osmocom-bb, as well as a virtual
BTS for simulation purpose later.
The sysmocom bts specific parts require hardware-specific header files
which are (at least currently) not publicly distributed.
Holger Hans Peter Freyther
Harald Welte