OsmocomBB

Right now, when configuring lower layers scheduler to receive notifications on a given TS set (through L1CTL-CFG_UL_TBF.req), it is not possible to state a start_time_fn with the meaning "apply the given configuration starting with that FN".

This is needed by upper layers when they receive TBF Starting Time from PCU, where they need to start using the TS at a given FN of time.

Since the RLC/MAC use the RTS.ind from lower layers, it needs to send the L1CTL-CFG_UL_TBF.req when it learns about the TBF to be created, so that it gets RTS.ind on the RLC/MAC scheduler which can then trigger FSM actions which move the TBF to the next state. However, right now, that means during the time frame "[L1CTL-CFG_UL_TBF.req .. TBFStartingTime] the upper layers are receiving RTS.ind where they have nothing to do.
Having this "start_time_fn" would spare the transmission of ticks to upper layers when they are not needed.

The idea in the lower layers is that if the field "start_time_present=1", then it queues the primitive until its internal clock reaches "start_time_fn=FN", then applies the config and hence sends RTS.ind to upper layers at that point.
Sending a L1CTL-CFG_UL_TBF.req with slot_mask=0x0 would also free the queues primitives if start_time_present==0.