pcuif: Submit data_req with len=0 as idle frames

This way PCU always answers DATA.ind and the BTS can still clearly
identify idle frames. It also simplifies testing and verification of
correct behavior.

Related: SYS#4919
Change-Id: Ife718eeed2af011479c03099ea109518f04567bc

src/gprs_rlcmac_sched.cpp

@@ -412,7 +412,7 @@ int gprs_rlcmac_rcv_rts_block(struct gprs_rlcmac_bts *bts,
 	uint8_t usf;
 	struct msgb *msg = NULL;
 	uint32_t poll_fn;
-	enum pcu_gsmtap_category gsmtap_cat;
+	enum pcu_gsmtap_category gsmtap_cat = PCU_GSMTAP_C_DL_DUMMY; /* init: make gcc happy */
 	bool tx_is_egprs = false;
 	bool require_gprs_only;
 	enum mcs_kind req_mcs_kind; /* Restrict CS/MCS if DL Data block is to be sent */
@@ -487,9 +487,9 @@ int gprs_rlcmac_rcv_rts_block(struct gprs_rlcmac_bts *bts,
 	}
 	/* Prio 3: send dummy control message if need to poll or USF */
 	else {
-		/* If there's no TBF attached to this PDCH, we can early skip
+		/* If there's no TBF attached to this PDCH, we can submit an empty
-		 * since there's nothing to transmit nor to poll/USF. This way
+		 * data_req since there's nothing to transmit nor to poll/USF. This
-		 * we help BTS energy saving (on TRX!=C0) by sending nothing
+		 * way we help BTS energy saving (on TRX!=C0) by sending nothing
 		 * instead of a dummy block. The early return is done here and
 		 * not at the start of the function because the condition below
 		 * (num_tbfs==0) may not be enough, because temporary dummy TBFs
@@ -505,13 +505,11 @@ int gprs_rlcmac_rcv_rts_block(struct gprs_rlcmac_bts *bts,
 		 * TRX0, since BTS is not preparing dummy bursts on idle TS for us */
 		skip_idle = skip_idle && trx != 0;
 #endif
-		if (skip_idle)
+		if (!skip_idle && (msg = sched_dummy())) {
-			return 0;
-		if ((msg = sched_dummy())) {
 			/* increase counter */
 			gsmtap_cat = PCU_GSMTAP_C_DL_DUMMY;
 		} else {
-			return -ENOMEM;
+			msg = NULL; /* submit empty frame */
 		}
 	}
 
@@ -521,6 +519,10 @@ int gprs_rlcmac_rcv_rts_block(struct gprs_rlcmac_bts *bts,
 		pdch->fn_without_cs14 = 0;
 	}
 
+	/* Used to measure the leak rate, count all blocks */
+	gprs_bssgp_update_frames_sent();
+
+	if (msg) {
 		/* msg is now available */
 		bts_do_rate_ctr_add(bts, CTR_RLC_DL_BYTES, msgb_length(msg));
 
@@ -529,13 +531,11 @@ int gprs_rlcmac_rcv_rts_block(struct gprs_rlcmac_bts *bts,
 		usf = usf_tbf ? usf_tbf->m_usf[ts] : USF_UNUSED;
 		msg->data[0] = (msg->data[0] & 0xf8) | usf;
 
-	/* Used to measure the leak rate, count all blocks */
-	gprs_bssgp_update_frames_sent();
-
 		/* Send to GSMTAP */
 		tap_n_acc(msg, bts, trx, ts, fn, gsmtap_cat);
+	}
 
-	/* send PDTCH/PACCH to L1 */
+	/* send PDTCH/PACCH to L1. msg=NULL accepted too (idle block) */
 	pcu_l1if_tx_pdtch(msg, bts, trx, ts, bts->trx[trx].arfcn, fn, block_nr);
 
 	return 0;

src/pcu_l1_if.cpp

@@ -212,6 +212,7 @@ static int pcu_tx_data_req(struct gprs_rlcmac_bts *bts, uint8_t trx, uint8_t ts,
 	data_req->trx_nr = trx;
 	data_req->ts_nr = ts;
 	data_req->block_nr = block_nr;
+	if (len)
 		memcpy(data_req->data, data, len);
 	data_req->len = len;
 
@@ -223,12 +224,20 @@ void pcu_l1if_tx_pdtch(msgb *msg, struct gprs_rlcmac_bts *bts, uint8_t trx, uint
 {
 #ifdef ENABLE_DIRECT_PHY
 	if (bts->trx[trx].fl1h) {
+		if (!msg) /* Simply skip sending idle frames to L1 */
+			return;
 		l1if_pdch_req(bts->trx[trx].fl1h, ts, 0, fn, arfcn, block_nr,
 			msg->data, msg->len);
 		msgb_free(msg);
 		return;
 	}
 #endif
+	if (!msg) {
+		pcu_tx_data_req(bts, trx, ts, PCU_IF_SAPI_PDTCH, arfcn, fn, block_nr,
+				NULL, 0);
+		return;
+	}
+
 	pcu_tx_data_req(bts, trx, ts, PCU_IF_SAPI_PDTCH, arfcn, fn, block_nr,
 			msg->data, msg->len);
 	msgb_free(msg);
@@ -243,10 +252,17 @@ void pcu_l1if_tx_ptcch(struct gprs_rlcmac_bts *bts,
 		gsmtap_send(the_pcu->gsmtap, arfcn, ts, GSMTAP_CHANNEL_PTCCH, 0, fn, 0, 0, data, data_len);
 #ifdef ENABLE_DIRECT_PHY
 	if (bts->trx[trx].fl1h) {
+		if (!data_len) /* Simply skip sending idle frames to L1 */
+			return;
 		l1if_pdch_req(bts->trx[trx].fl1h, ts, 1, fn, arfcn, block_nr, data, data_len);
 		return;
 	}
 #endif
+	if (!data_len) {
+		pcu_tx_data_req(bts, trx, ts, PCU_IF_SAPI_PTCCH, arfcn, fn, block_nr, NULL, 0);
+		return;
+	}
+
 	pcu_tx_data_req(bts, trx, ts, PCU_IF_SAPI_PTCCH, arfcn, fn, block_nr, data, data_len);
 }
 
@@ -544,8 +560,11 @@ int pcu_rx_rts_req_ptcch(struct gprs_rlcmac_bts *bts, uint8_t trx, uint8_t ts,
 		 * TRX0, since BTS is not preparing dummy bursts on idle TS for us: */
 		skip_idle = skip_idle && trx != 0;
 #endif
-	if (skip_idle)
+	if (skip_idle) {
+		pcu_l1if_tx_ptcch(bts, trx, ts, bts->trx[trx].arfcn, fn, block_nr,
+				  NULL, 0);
 		return 0;
+	}
 
 	pcu_l1if_tx_ptcch(bts, trx, ts, bts->trx[trx].arfcn, fn, block_nr,
 			  pdch->ptcch_msg, GSM_MACBLOCK_LEN);