update DTX fill frame test expectations

Fix an off-by-one in frame number comparison: Ensure that we
won't stop testing until after fn + 104 has been received.

The DTX test case would never pass since the alt statement
was always repeated even if enough frames had been received.
Fix this by moving code which runs before frame fn + 104 is
received into an 'else' cause.

We receive SACCH frames in DTX mode so we must account for them.
Introduce separate counters for SACCH and non-SACCH fill frames
to make test failure diagnosis easier. Note that we cannot expect
a specific amount of SACCH frames during a particular test run
since their amount depends on what the current frame number window
happens to be. We can however add the counters for SACCH and
non-SACCH fill frames and obtain a meaningful result.

Change-Id: Ie573b54ab5654f027c470aa7a565d2b5b97dc74b
Related: OS#1950

1 files changed, 47 insertions, 19 deletions

diff --git a/bts/BTS_Tests.ttcn b/bts/BTS_Tests.ttcn
index fd2e50f9..67f302f3 100644
--- a/bts/BTS_Tests.ttcn
+++ b/bts/BTS_Tests.ttcn
@@ -3836,10 +3836,16 @@ function f_test_l2_fill_frames(boolean dtxd) runs on ConnHdlr {
 	var octetstring l2_fill_frame_sacch := substr(l2_fill_frame, 0, lengthof(l2_fill_frame) - 2);
 	var GsmFrameNumber first_fn;
 	var boolean is_first_frame := true;
-	var integer nfill_frames := 0;
-	const integer dtx_tchf_mod := 104;
+	var integer nfill_frames_sacch := 0;
+	var integer nfill_frames_nonsacch := 0;
+	var integer expected_fill_frames := 10000; /* initial value causes test failure if not overridden */
 	/* Frames numbers (mod 104) for which a fill frame is expected on TCHF if DTX is enabled. */
 	var Integers required_tdma_frames_dtx_tchf := { 52, 53, 54, 55, 56, 57, 58, 59 };
+	const integer frame_dtx_tchf_mod := 104;
+	/* Frame numbers (mod 104) for which a fill frame is expected at the L1SAP level,
+	 * which operates in terms of blocks rather than frames. */
+	var Integers required_tdma_blocks_dtx_tchf := { 52, 56 };
+	const integer block_dtx_tchf_mod := 26;
 	timer T := 5.0;
 
 	f_l1_tune(L1CTL);
@@ -3876,32 +3882,51 @@ function f_test_l2_fill_frames(boolean dtxd) runs on ConnHdlr {
 				f_L1CTL_DM_REL_REQ(L1CTL, g_chan_nr);
 				setverdict(fail, "Received fill frame on non-TCH/F channel; DTX is only allowed on TCH/F!");
 			}
-			if (fn >= first_fn + dtx_tchf_mod) {
+			if (fn > first_fn + frame_dtx_tchf_mod) {
 				T.stop;
 				f_rsl_chan_deact();
 				f_L1CTL_DM_REL_REQ(L1CTL, g_chan_nr);
-				/* With DTX enabled we can expect at least 1 fill frame every 104 frames. */
-				if (nfill_frames < 1) {
-					setverdict(fail);
+
+				/* With DTX enabled we can expect at least 3 fill frames for every 104 frames.
+				 * 2 SACCH, 1 TCH/F */
+				expected_fill_frames := 3;
+
+				if (nfill_frames_sacch + nfill_frames_nonsacch < expected_fill_frames) {
+					log("received only ", nfill_frames_sacch, "+", nfill_frames_nonsacch,
+					    " (SACCH+other) out of ", expected_fill_frames, " expected fill frames");
+					setverdict(fail, "Not enough fill frames received");
 				} else {
 					setverdict(pass);
 				}
-			}
-			for (var integer i := 0; i < lengthof(required_tdma_frames_dtx_tchf); i := i + 1) {
-				if (fn mod dtx_tchf_mod == required_tdma_frames_dtx_tchf[i]) {
-					nfill_frames := nfill_frames + 1;
+			} else {
+				if (dl.dl_info.link_id.c == SACCH) {
+					nfill_frames_sacch := nfill_frames_sacch + 1;
 					repeat;
 				}
+				/* On DTX TCH/F channels, fill frames occur only for specific frame numbers mod 104.
+				 * Furthermore, the L1SAP layer gives us frame numbers for the start of a block so
+				 * we should only see the subset of frames numbers which correspond to a block boundary.
+				 * TCH/F blocks are defined to start at 0,4,8,13,17,21 (modulo 26) */
+				for (var integer i := 0; i < lengthof(required_tdma_blocks_dtx_tchf); i := i + 1) {
+					if (fn mod frame_dtx_tchf_mod == required_tdma_blocks_dtx_tchf[i]) {
+						nfill_frames_nonsacch := nfill_frames_nonsacch + 1;
+						repeat;
+					}
+				}
+				log("Received DTX TCH fill frame with bad frame number: ", fn,
+				    " (mod ", frame_dtx_tchf_mod, ": ", fn mod frame_dtx_tchf_mod, ")",
+				    " (mod ", block_dtx_tchf_mod, ": ", fn mod block_dtx_tchf_mod, ")");
+				f_rsl_chan_deact();
+				f_L1CTL_DM_REL_REQ(L1CTL, g_chan_nr);
+				setverdict(fail, "Unexpected L2 fill frame received on Um");
 			}
-			log("Received DTX TCH fill frame with bad frame number: ", fn,
-			    " (mod ", dtx_tchf_mod, ": ", fn mod dtx_tchf_mod, ")");
-			f_rsl_chan_deact();
-			f_L1CTL_DM_REL_REQ(L1CTL, g_chan_nr);
-			setverdict(fail, "Unexpected L2 fill frame received on Um");
 		} else {
-			nfill_frames := nfill_frames + 1;
-			if (fn >= first_fn + dtx_tchf_mod) {
-				var integer expected_fill_frames;
+			if (dl.dl_info.link_id.c == SACCH) {
+				nfill_frames_sacch := nfill_frames_sacch + 1;
+			} else {
+				nfill_frames_nonsacch := nfill_frames_nonsacch + 1;
+			}
+			if (fn > first_fn + frame_dtx_tchf_mod) {
 				T.stop;
 				if (f_g_chan_is_tchf()) {
 					/* Without DTX we can expect 25 fill frames for every 104 frames.
@@ -3921,9 +3946,12 @@ function f_test_l2_fill_frames(boolean dtxd) runs on ConnHdlr {
 
 				f_rsl_chan_deact();
 				f_L1CTL_DM_REL_REQ(L1CTL, g_chan_nr);
-				if (nfill_frames >= expected_fill_frames) {
+
+				if (nfill_frames_sacch + nfill_frames_nonsacch >= expected_fill_frames) {
 					setverdict(pass);
 				} else {
+					log("received only ", nfill_frames_sacch, "+", nfill_frames_nonsacch,
+					    " (SACCH+other) out of ", expected_fill_frames, " expected fill frames");
 					setverdict(fail, "Not enough fill frames received");
 				}
 			} else {