fn-advance and rts-advance seem to do the same thing?
There are two osmo-bts-trx specific settings: fn-advance and rts-advance.
- they seem to do exactly the same thing: Advance the frame number in order to compensate for delays between osmo-trx and osmo-bts-trx
- they seem to be used both only in scheduler_trx.c:trx_sched_fn() within very few lines from each other
- they are simply added together.
In the default configuration, there's 20 frames of fn-advance and 5 frames of rts-advance, accounting for a total advance of 25 frames (of 4.616ms each, totalling to 115.4ms).
The documentation also seems wrong, as it claims rts-advance is specific to the PCU while fn-advance is generic. However, I cannot see any difference between those two. Am I missing something?
#1 Updated by laforge over 1 year ago
- Status changed from New to In Progress
- % Done changed from 0 to 80
As sylvain points out, only fn-advance is used when pulling bursts out of the bottom of the osmo-bts scheduler. The sum of fn-advance and rts-advance is used when pulling MAC blocks out of Layer2 (LAPDm, RTP, PCUIF).
I've updated the related documentation in https://gerrit.osmocom.org/c/osmo-bts/+/14334