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osmo-bts-trx: check if scheduling of [dummy] FACCH/H is allowed

Change-Id: I6f8af140a6ccf3d5fd7b98f6cb5c18e2c5e2f61b
Related: SYS#5919, OS#4823
---
M src/common/scheduler.c
M src/osmo-bts-trx/sched_lchan_tchh.c
2 files changed, 9 insertions(+), 1 deletion(-)

git pull ssh://gerrit.osmocom.org:29418/osmo-bts refs/changes/36/27836/1

diff --git a/src/common/scheduler.c b/src/common/scheduler.c
index 96189ef..422572d 100644
--- a/src/common/scheduler.c
+++ b/src/common/scheduler.c
@@ -998,7 +998,7 @@
 
 /* FACCH/H channel mapping for Downlink (see 3GPP TS 45.002, table 1).
  * This mapping is valid for both FACCH/H(0) and FACCH/H(1). */
-static const uint8_t sched_tchh_dl_facch_map[26] = {
+const uint8_t sched_tchh_dl_facch_map[26] = {
 	[4]  = 1, /* FACCH/H(0): B0(4,6,8,10,13,15) */
 	[5]  = 1, /* FACCH/H(1): B0(5,7,9,11,14,16) */
 	[13] = 1, /* FACCH/H(0): B1(13,15,17,19,21,23) */
diff --git a/src/osmo-bts-trx/sched_lchan_tchh.c b/src/osmo-bts-trx/sched_lchan_tchh.c
index e9e59e7..a163b31 100644
--- a/src/osmo-bts-trx/sched_lchan_tchh.c
+++ b/src/osmo-bts-trx/sched_lchan_tchh.c
@@ -75,6 +75,9 @@
 	[3]  = 1, /* FACCH/H(1): B2(18,20,22,24,1,3) */
 };
 
+/* TDMA frame number of burst 'a' is used as the table index. */
+extern const uint8_t sched_tchh_dl_facch_map[26];
+
 /*! \brief a single TCH/H burst was received by the PHY, process it */
 int rx_tchh_fn(struct l1sched_ts *l1ts, const struct trx_ul_burst_ind *bi)
 {
@@ -406,6 +409,11 @@
 		};
 
 		LOGL1SB(DL1P, LOGL_INFO, l1ts, br, "No TCH or FACCH prim for transmit.\n");
+
+		/* FACCH/H can only be scheduled at specific TDMA offset */
+		if (!sched_tchh_dl_facch_map[br->fn % 26])
+			goto send_burst; /* send garbage */
+
 		gsm0503_tch_hr_encode(*bursts_p, dummy, sizeof(dummy));
 		chan_state->dl_ongoing_facch = 1;
 		chan_state->dl_facch_bursts = 6;

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