Pick unreserved UL FN when allocating an SBA

Make sure an unreserved FN is picked and reserved when allocating and
scheduling an SBA.
In practice this has no change in behavior right now, since anyway using
an offset of 52 FNs ensure no USF or POLL has alredy been scheduled that
far in the future. Since it's also impossible to allocate more than 1
SBA per PDCH and RTS FN, we are also safe about multiple SBAs being
allocated, because we use a hardcoded offset of 52.
However, that could change in the future, when we dynamically tweak the
current offset of 52 FN based on information from BTS about its AGCH
queue load:
* If load is high, we may need to increase the offset since it
will take more time for the BTS to transmit the TBF and hence we must
reserve a TBF starting time further in the future (higher FN).
* If load turns low, we may schedule next SBA a bit more nearby in time
  than the previously allocated SBA, hence here there could be a
  collision.

Related: OS#5020
Change-Id: I2d4e21e2307de6c17748e8da5c7e149c947a7eb9

2 files changed, 34 insertions, 0 deletions

diff --git a/tests/ulc/PdchUlcTest.cpp b/tests/ulc/PdchUlcTest.cpp
index 00991012..f0e8dd91 100644
--- a/tests/ulc/PdchUlcTest.cpp
+++ b/tests/ulc/PdchUlcTest.cpp
@@ -212,6 +212,30 @@ static void test_fn_wrap_around()
 	printf("=== end: %s ===\n", __FUNCTION__);
 }
 
+static void test_next_free_fn_sba()
+{
+	printf("=== start: %s ===\n", __FUNCTION__);
+	struct gprs_rlcmac_bts *bts = bts_alloc(the_pcu, 0);
+	struct gprs_rlcmac_pdch *pdch = &bts->trx[0].pdch[0];
+	struct gprs_rlcmac_sba *sba1, *sba2, *sba3, *sba4;
+
+	pdch->last_rts_fn = 52;
+	printf("*** ALLOC 1 SBA FN=%" PRIu32 ":\n", pdch->last_rts_fn);
+	sba1 = sba_alloc(bts, pdch, 0);
+	print_ulc_nodes(pdch->ulc);
+
+	pdch->last_rts_fn = 65;
+	printf("*** ALLOC 3 SBA FN=%" PRIu32 ":\n", pdch->last_rts_fn);
+	sba2 = sba_alloc(bts, pdch, 0);
+	sba3 = sba_alloc(bts, pdch, 0);
+	sba4 = sba_alloc(bts, pdch, 0);
+	print_ulc_nodes(pdch->ulc);
+	(void)sba1; (void)sba2; (void)sba3; (void)sba4;
+
+	talloc_free(bts);
+	printf("=== end: %s ===\n", __FUNCTION__);
+}
+
 int main(int argc, char **argv)
 {
 	tall_pcu_ctx = talloc_named_const(NULL, 1, "pdch_ulc test context");
@@ -231,6 +255,7 @@ int main(int argc, char **argv)
 
 	test_reserve_multiple();
 	test_fn_wrap_around();
+	test_next_free_fn_sba();
 
 	talloc_free(the_pcu);
 	return EXIT_SUCCESS;
diff --git a/tests/ulc/PdchUlcTest.ok b/tests/ulc/PdchUlcTest.ok
index f20fb309..5bab5cc4 100644
--- a/tests/ulc/PdchUlcTest.ok
+++ b/tests/ulc/PdchUlcTest.ok
@@ -247,3 +247,12 @@ FN=34 type=POLL
 FN=39 type=POLL
 *** EXPIRE FN=43:
 === end: test_fn_wrap_around ===
+=== start: test_next_free_fn_sba ===
+*** ALLOC 1 SBA FN=52:
+FN=104 type=SBA
+*** ALLOC 3 SBA FN=65:
+FN=104 type=SBA
+FN=117 type=SBA
+FN=121 type=SBA
+FN=125 type=SBA
+=== end: test_next_free_fn_sba ===