edge: Compare len instead of using cs.isCombinable

Comparing the coding scheme properties doesn't seem to be strong
enough, since create_dl_acked_block(fn, ts, index, index2) sometimes
had to combine data units of different size this way.

Check the registered size of the BSN blocks instead, since these must
match if two blocks are to be combined in a single RLC data message
with MCS7-9.

It is not yet clear, what exactly goes wrong with the current
implementation, but this commit fixes the problem which trigger the
assertion in create_dl_acked_block.

Sponsored-by: On-Waves ehf

2 files changed, 15 insertions, 12 deletions

diff --git a/src/tbf.h b/src/tbf.h
index 6c030d23..ad8ad4c2 100644
--- a/src/tbf.h
+++ b/src/tbf.h
@@ -407,7 +407,7 @@ protected:
 	};
 
 	int take_next_bsn(uint32_t fn, int previous_bsn,
-		GprsCodingScheme *next_cs);
+		bool *may_combine);
 	bool restart_bsn_cycle();
 	int create_new_bsn(const uint32_t fn, GprsCodingScheme cs);
 	struct msgb *create_dl_acked_block(const uint32_t fn, const uint8_t ts,
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index e2521f84..6d4209f1 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -355,9 +355,10 @@ bool gprs_rlcmac_dl_tbf::restart_bsn_cycle()
 }
 
 int gprs_rlcmac_dl_tbf::take_next_bsn(uint32_t fn,
-	int previous_bsn, GprsCodingScheme *next_cs)
+	int previous_bsn, bool *may_combine)
 {
 	int bsn;
+	int data_len2, force_data_len = -1;
 	GprsCodingScheme cs2;
 	GprsCodingScheme force_cs;
 
@@ -367,6 +368,7 @@ int gprs_rlcmac_dl_tbf::take_next_bsn(uint32_t fn,
 		force_cs = m_rlc.block(previous_bsn)->cs;
 		if (!force_cs.isEgprs())
 			return -1;
+		force_data_len = m_rlc.block(previous_bsn)->len;
 	}
 
 	if (bsn >= 0) {
@@ -378,7 +380,8 @@ int gprs_rlcmac_dl_tbf::take_next_bsn(uint32_t fn,
 			return -1;
 
 		cs2 = m_rlc.block(bsn)->cs;
-		if (force_cs && !cs2.isCombinable(force_cs))
+		data_len2 = m_rlc.block(bsn)->len;
+		if (force_data_len > 0 && force_data_len != data_len2)
 			return -1;
 		LOGP(DRLCMACDL, LOGL_DEBUG, "- Resending BSN %d\n", bsn);
 		/* re-send block with negative aknowlegement */
@@ -390,14 +393,14 @@ int gprs_rlcmac_dl_tbf::take_next_bsn(uint32_t fn,
 			m_window.v_a());
 		bts->rlc_restarted();
 		if (restart_bsn_cycle())
-			return take_next_bsn(fn, previous_bsn, next_cs);
+			return take_next_bsn(fn, previous_bsn, may_combine);
 	} else if (dl_window_stalled()) {
 		LOGP(DRLCMACDL, LOGL_NOTICE, "- Restarting at BSN %d, "
 			"because the window is stalled.\n",
 			m_window.v_a());
 		bts->rlc_stalled();
 		if (restart_bsn_cycle())
-			return take_next_bsn(fn, previous_bsn, next_cs);
+			return take_next_bsn(fn, previous_bsn, may_combine);
 	} else if (have_data()) {
 		/* New blocks may be send */
 		cs2 = force_cs ? force_cs : current_cs();
@@ -412,14 +415,14 @@ int gprs_rlcmac_dl_tbf::take_next_bsn(uint32_t fn,
 			m_window.v_a());
 		bts->rlc_restarted();
 		if (restart_bsn_cycle())
-			return take_next_bsn(fn, previous_bsn, next_cs);
+			return take_next_bsn(fn, previous_bsn, may_combine);
 	} else {
 		/* Nothing left to send, create dummy LLC commands */
 		LOGP(DRLCMACDL, LOGL_DEBUG,
 			"- Sending new dummy block at BSN %d, CS=%s\n",
 			m_window.v_s(), current_cs().name());
 		bsn = create_new_bsn(fn, current_cs());
-		/* Don't send a second block */
+		/* Don't send a second block, so don't set cs2 */
 	}
 
 	if (bsn < 0) {
@@ -430,7 +433,7 @@ int gprs_rlcmac_dl_tbf::take_next_bsn(uint32_t fn,
 		bts->rlc_resent();
 	}
 
-	*next_cs = cs2;
+	*may_combine = cs2.numDataBlocks() > 1;
 
 	return bsn;
 }
@@ -442,18 +445,18 @@ int gprs_rlcmac_dl_tbf::take_next_bsn(uint32_t fn,
 struct msgb *gprs_rlcmac_dl_tbf::create_dl_acked_block(uint32_t fn, uint8_t ts)
 {
 	int bsn, bsn2 = -1;
-	GprsCodingScheme cs, next_cs;
+	bool may_combine;
 
 	LOGP(DRLCMACDL, LOGL_DEBUG, "%s downlink (V(A)==%d .. "
 		"V(S)==%d)\n", tbf_name(this),
 		m_window.v_a(), m_window.v_s());
 
-	bsn = take_next_bsn(fn, -1, &next_cs);
+	bsn = take_next_bsn(fn, -1, &may_combine);
 	if (bsn < 0)
 		return NULL;
 
-	if (next_cs.numDataBlocks() > 1)
-		bsn2 = take_next_bsn(fn, bsn, &next_cs);
+	if (may_combine)
+		bsn2 = take_next_bsn(fn, bsn, &may_combine);
 
 	return create_dl_acked_block(fn, ts, bsn, bsn2);
 }