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Hello Jenkins Builder,

I'd like you to reexamine a change. Please visit

https://gerrit.osmocom.org/c/osmocom-bb/+/32575

to look at the new patch set (#3).

Change subject: trxcon: get rid of the timer driven clock module ......................................................................

trxcon: get rid of the timer driven clock module

trxcon was heavily inspired by osmo-bts-trx, and among with many other scheduling related parts also inherited the timer driven clock module.

This clock module is driving the Uplink burst scheduling, just like it does drive the Downlink burst scheduling in osmo-bts-trx. Just like in osmo-bts-trx, the clock module relies on periodic CLCK indications from the PHY, which are needed to compensate for the clock drifting.

The key difference is that trxcon is using Downlink bursts as the CLCK indications, see 'bi.fn % 51' in trx_data_rx_cb(). This is possible because the MS is a clock slave of the BTS: the MS PHY needs to sync its freq. and clock first, and only after that it can Rx and Tx.

So far we've had no problems with the clock module in trxcon until we started adding GPRS support and integrated the l1gprs. While the CS domain is quite flexible in terms of timings and delays, the PS domain is a lot more sensetive to the timing issues.

Sometimes it happens that the trxcon's clock module is ticking quicker than it should, resulting in Uplink PDCH blocks being scheduled earlier than the respective Downlink PDCH blocks are received:

20230502021957724 l1sched_pull_burst(): PDTCH/U Tx time (fn=56103) 20230502021957744 (PDCH-7) Rx DL BLOCK.ind (fn=56103, len=23): ... 20230502021957747 l1sched_pull_burst(): PDTCH/U Tx time (fn=56108) 20230502021957765 l1sched_pull_burst(): PDTCH/U Tx time (fn=56112) 20230502021957767 (PDCH-7) Rx DL BLOCK.ind (fn=56108, len=23): ... 20230502021957768 (PDCH-7) Rx UL BLOCK.req (fn=56112, len=54): ... 20230502021957784 l1sched_pull_burst(): PDTCH/U Tx time (fn=56116) 20230502021957784 TS7-PDTCH dropping Tx primitive (current Fn=56116, prim Fn=56112)

This is impossible in reality, because Uplink is intentionally lagging behind Downlink by 3 TDMA timeslot periods. In a virtual setup this causes sporadic dropping of Uplink PDCH blocks, as can be seen from the logging snippet above, and significantly degrades the RLC/MAC performance for GPRS.

Let's remove the internal clock module and trigger the Uplink burst transmission each time we receive a Downlink burst. This helps to overcome the GPRS scheduling issues and replicates the approach of osmo-trx-ms more closely.

Change-Id: Ic8a5b6277c6b16392026e0557376257d71c9d230 Related: OS#5500 --- M src/host/trxcon/include/osmocom/bb/l1sched/l1sched.h M src/host/trxcon/include/osmocom/bb/trxcon/phyif.h M src/host/trxcon/include/osmocom/bb/trxcon/trx_if.h M src/host/trxcon/include/osmocom/bb/trxcon/trxcon.h M src/host/trxcon/src/Makefile.am D src/host/trxcon/src/sched_clck.c M src/host/trxcon/src/sched_trx.c M src/host/trxcon/src/trx_if.c M src/host/trxcon/src/trxcon_inst.c M src/host/trxcon/src/trxcon_main.c M src/host/trxcon/src/trxcon_shim.c 11 files changed, 68 insertions(+), 263 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/osmocom-bb refs/changes/75/32575/3