Unlike xCCH, TCH/H channels are using block diagonal interleaving,
so every single burst carries 57 bits of one traffic frame, and 57
bits of another one. Moreover, unlike TCH/F where both traffic
and FACCH/F frames are interleaved over 8 bursts, a FACCH/H is
interleaved over 6 bursts, while a traffic frame is interleaved
over 4 bursts.
This is why a TCH/H burst transmission can't be initiated on
an arbitrary TDMA frame number. It shall be aligned as of
stated in GSM 05.02, clause 7, table 1.
This change introduces two basic functions:
- sched_tchh_block_map_fn - checks if a TCH/H block transmission
can be initiated / finished on a given frame number
and a given channel type;
- sched_tchh_block_dl_first_fn - calculates TDMA frame number of
the first burst using given frame number of the last burst;
and some auxiliary wrappers to simplify the usage of
sched_tchh_block_map_fn().
Change-Id: Iaf4cb33f1b79df23f8a90c8b14ebe0cd9907fbb9
The 'normal' math operations, such as addition and substraction,
are not applicable for TDMA frame numbers because they may result
in out-of-range values.
Having TDMA frame math helpers in a single place would allow
one to avoid possible out-of-range result mistakes.
Change-Id: Ibb66ba846cc3d6c2eaa88414569e5f3751128047
Use osmo_clock_gettime() to read the monotonic clock instead
of gettimeofday() which could drift backwards.
This requires switching the scheduler clock from struct timeval
to struct timespec. Expand some variables to 64 bits in order
to keep types used in calculations compatible.
The previous implementation unconditionally subtracted microsecond
values from different time measurements, causing overflow if the
current measurement was taken in less of a fraction of a second
than the past measurement. Use timespecsub() for the subtraction
instead which accounts for fractions of a second correctly.
Change-Id: Ic93f90685c6d6dc28dfc4ad48c998e0eac113cf8
Related: OS#3467
In order to get the transceiver more time to process bursts,
the L1 scheduler should process the frames and send the bursts
in advance (a few frames before), like OsmoBTS does. By default,
the advance value is 20 frames, but this can be adjusted using a
new command line option of trxcon '-f'.
Change-Id: Ic258a169f3554f931d6277e18ca060d029b77f32
The core of scheduler is a simple clock counter, which relays
on system time for now. One was a bit simplified and migrated
from OsmoBTS.
Due to system time is not an ideal clock source, the counter
should be periodically corrected by clock indications from BTS.
Change-Id: I27d85bd3e2c8bca3f876f73517027b9fe43c9825
Vadim Yanitskiy