[S] Change in osmocom-bb[master]: trx_toolkit/clck_gen: Fix clock generator to emit ticks with exactly ...

fixeria has submitted this change. ( https://gerrit.osmocom.org/c/osmocom-bb/+/39392?usp=email ) Change subject: trx_toolkit/clck_gen: Fix clock generator to emit ticks with exactly GSM frame period ...................................................................... trx_toolkit/clck_gen: Fix clock generator to emit ticks with exactly GSM frame period Since fake_trx beginning in 3187c8e6 (target/fake_trx: initial release of virtual transceiver) CLCKGen was tuned to emitting ticks with sleep period being time of 1 GSM frame _decreased_ a bit by "Average loop back delay". The idea for this decrease probably was to compensate the time spent in each tick handler, so that combined sleep + tick work would occupy time of 1 GSM frame more or less. The idea of using hardcoded compensation turned out to be not very good, because for the overall tick period to be exactly as defined the compensation should be dynamic and take into account time spent in each tick handler. For example on one machine "loopback delay" is one value, while on another it will be another value. And if we attach more work to tick handler, like it already happened with adding tx queue, the compensation needs to take all that into account as well. abc63d8d (trx_toolkit/clck_gen.py: Fix clock generator not to accumulate timing error) explains the problem in detail and adds dynamic compensation so that the tick period stays as defined instead of drifting. But it missed to adjust CLCKgen to stop decreasing desired tick period a bit by "average loop back delay". So after that patch, because CLCKgen now follows desired period without drifting, its period was 4.615ms - 0.09ms instead of exact 4.615ms, which resulted in e.g. fake_trx and bts-trx clocks to become constantly dissynchronized with the following emitted by bts-trx non-stop: 20250122135431420 <0006> scheduler_trx.c:576 GSM clock skew: old fn=0, new fn=102 20250122135431882 <0006> scheduler_trx.c:604 We were 3 FN slower than TRX, compensated 20250122135432344 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135432805 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135433267 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135433728 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135434190 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135434651 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135435113 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135435575 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135436036 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135436498 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135436959 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated 20250122135437421 <0006> scheduler_trx.c:604 We were 2 FN slower than TRX, compensated ... What happens here is that there are ~ 216 GSM frames every second, and since fake_trx drifts by 0.09ms every frame, it results in drifting by ~ 20ms every second. Which results in "2 FN slower than TRX" emitted approximately twice per second as above log excerpt confirms. -> Fix this by adjusting CLCKgen to emit ticks with exactly GSM frame period by default. Change-Id: Ie12fbe8138bac1398805fa270b869e7a333fcba0 --- M src/target/trx_toolkit/clck_gen.py M src/target/trx_toolkit/test_clck_gen.py 2 files changed, 6 insertions(+), 4 deletions(-) Approvals: fixeria: Looks good to me, approved Jenkins Builder: Verified pespin: Looks good to me, but someone else must approve diff --git a/src/target/trx_toolkit/clck_gen.py b/src/target/trx_toolkit/clck_gen.py index bf56f64..c6da8f6 100755 --- a/src/target/trx_toolkit/clck_gen.py +++ b/src/target/trx_toolkit/clck_gen.py @@ -34,9 +34,6 @@ SEC_DELAY_US = 1000 * 1000 GSM_FRAME_US = 4615.0 - # Average loop back delay - LO_DELAY_US = 90.0 - def __init__(self, clck_links, clck_start = 0, ind_period = 102): # This event is needed to control the thread self._breaker = threading.Event() @@ -47,7 +44,7 @@ self.clck_start = clck_start # Calculate counter time - self.ctr_interval = self.GSM_FRAME_US - self.LO_DELAY_US + self.ctr_interval = self.GSM_FRAME_US self.ctr_interval /= self.SEC_DELAY_US # (Optional) clock consumer diff --git a/src/target/trx_toolkit/test_clck_gen.py b/src/target/trx_toolkit/test_clck_gen.py index a920ce1..92e5e55 100644 --- a/src/target/trx_toolkit/test_clck_gen.py +++ b/src/target/trx_toolkit/test_clck_gen.py @@ -63,6 +63,11 @@ finally: clck.stop() + # verify that default tick interval is 1 TDMA frame exactly + def test_period_is_gsm_frame(self): + clck = clck_gen.CLCKGen([]) + self.assertEqual(clck.ctr_interval, 4.615e-3) + if __name__ == '__main__': unittest.main() -- To view, visit https://gerrit.osmocom.org/c/osmocom-bb/+/39392?usp=email To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings?usp=email Gerrit-MessageType: merged Gerrit-Project: osmocom-bb Gerrit-Branch: master Gerrit-Change-Id: Ie12fbe8138bac1398805fa270b869e7a333fcba0 Gerrit-Change-Number: 39392 Gerrit-PatchSet: 1 Gerrit-Owner: kirr &lt;kirr(a)nexedi.com&gt; Gerrit-Reviewer: Jenkins Builder Gerrit-Reviewer: fixeria &lt;vyanitskiy(a)sysmocom.de&gt; Gerrit-Reviewer: pespin &lt;pespin(a)sysmocom.de&gt; Gerrit-CC: osmith &lt;osmith(a)sysmocom.de&gt;