Handle Immediate assignment reject

When RACH is received, PCU will generate the Immediate assignment reject
message if no resources are present. The encoding is done based on section
9.1.20 of 44.018 version 11.7.0 Release 11. This patch also includes the
test case to validate the generated Immediate assignment reject message.

This patch is integration tested on Osmo-trx setup with Ettus B210 board
and LG F70 MS with some simulation code changes in Osmo-pcu.

Change-Id: I3d33e2b9746fa4f338fad0e6b63b1c5f07de6f9b

3 files changed, 149 insertions, 42 deletions

diff --git a/src/bts.cpp b/src/bts.cpp
index 4aa5c2c..4e6b5e9 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -475,32 +475,42 @@ int BTS::rcv_rach(uint16_t ra, uint32_t Fn, int16_t qta, uint8_t is_11bit,
 	uint8_t trx_no, ts_no = 0;
 	uint8_t sb = 0;
 	uint32_t sb_fn = 0;
-	int rc;
+	int rc = 0;
 	int plen;
 	uint8_t usf = 7;
-	uint8_t tsc, ta = qta2ta(qta);
+	uint8_t tsc = 0, ta = qta2ta(qta);
 	uint16_t ms_class = 0;
 	uint16_t priority = 0;
+	bool failure = false;
 
 	rach_frame();
 
-	LOGP(DRLCMAC, LOGL_DEBUG, "MS requests UL TBF on RACH, so we provide "
-		"one:\n");
+	LOGP(DRLCMAC, LOGL_DEBUG, "MS requests UL TBF on RACH, "
+		"so we provide one \n"
+		"ra=0x%02x Fn=%u qta=%d is_11bit=%d:\n", ra, Fn, qta, is_11bit);
 
 	sb = is_single_block(ra, burst_type, is_11bit, &ms_class, &priority);
 
 	if (sb) {
 		rc = sba()->alloc(&trx_no, &ts_no, &sb_fn, ta);
-		if (rc < 0)
-			return rc;
-		LOGP(DRLCMAC, LOGL_DEBUG, "RX: [PCU <- BTS] RACH qbit-ta=%d "
-			"ra=0x%02x, Fn=%d (%d,%d,%d), SBFn=%d\n",
-			qta, ra,
-			Fn, (Fn / (26 * 51)) % 32, Fn % 51, Fn % 26,
-			sb_fn);
-		LOGP(DRLCMAC, LOGL_INFO, "TX: Immediate Assignment Uplink "
-			"(AGCH)\n");
-		tsc = m_bts.trx[trx_no].pdch[ts_no].tsc;
+		if (rc < 0) {
+			failure = true;
+			LOGP(DRLCMAC, LOGL_NOTICE, "No PDCH resource for "
+					"single block allocation."
+					"sending Immediate "
+					"Assignment Uplink (AGCH) reject\n");
+		} else {
+			tsc = m_bts.trx[trx_no].pdch[ts_no].tsc;
+
+			LOGP(DRLCMAC, LOGL_DEBUG, "RX: [PCU <- BTS] RACH "
+				" qbit-ta=%d ra=0x%02x, Fn=%d (%d,%d,%d),"
+				" SBFn=%d\n",
+				qta, ra,
+				Fn, (Fn / (26 * 51)) % 32, Fn % 51, Fn % 26,
+				sb_fn);
+			LOGP(DRLCMAC, LOGL_INFO, "TX: Immediate Assignment "
+				"Uplink (AGCH)\n");
+		}
 	} else {
 		// Create new TBF
 		#warning "Copy and paste with other routines.."
@@ -515,47 +525,60 @@ int BTS::rcv_rach(uint16_t ra, uint32_t Fn, int16_t qta, uint8_t is_11bit,
 		}
 
 		if (!tbf) {
-			LOGP(DRLCMAC, LOGL_NOTICE, "No PDCH resource\n");
-			/* FIXME: send reject */
-			return -EBUSY;
+			LOGP(DRLCMAC, LOGL_NOTICE, "No PDCH resource sending "
+					"Immediate Assignment Uplink (AGCH) "
+					"reject\n");
+			rc = -EBUSY;
+			failure = true;
+		} else {
+			tbf->set_ta(ta);
+			tbf->set_state(GPRS_RLCMAC_FLOW);
+			tbf->state_flags |= (1 << GPRS_RLCMAC_FLAG_CCCH);
+			tbf_timer_start(tbf, 3169, m_bts.t3169, 0);
+			LOGP(DRLCMAC, LOGL_DEBUG, "%s [UPLINK] START\n",
+					tbf_name(tbf));
+			LOGP(DRLCMAC, LOGL_DEBUG, "%s RX: [PCU <- BTS] RACH "
+					"qbit-ta=%d ra=0x%02x, Fn=%d "
+					" (%d,%d,%d)\n",
+					tbf_name(tbf),
+					qta, ra, Fn, (Fn / (26 * 51)) % 32,
+					Fn % 51, Fn % 26);
+			LOGP(DRLCMAC, LOGL_INFO, "%s TX: START Immediate "
+					"Assignment Uplink (AGCH)\n",
+					tbf_name(tbf));
+			trx_no = tbf->trx->trx_no;
+			ts_no = tbf->first_ts;
+			usf = tbf->m_usf[ts_no];
+			tsc = tbf->tsc();
 		}
-		tbf->set_ta(ta);
-		tbf->set_state(GPRS_RLCMAC_FLOW);
-		tbf->state_flags |= (1 << GPRS_RLCMAC_FLAG_CCCH);
-		tbf_timer_start(tbf, 3169, m_bts.t3169, 0);
-		LOGP(DRLCMAC, LOGL_DEBUG, "%s [UPLINK] START\n",
-			tbf_name(tbf));
-		LOGP(DRLCMAC, LOGL_DEBUG, "%s RX: [PCU <- BTS] RACH "
-			"qbit-ta=%d ra=0x%02x, Fn=%d (%d,%d,%d)\n",
-			tbf_name(tbf),
-			qta, ra, Fn, (Fn / (26 * 51)) % 32, Fn % 51, Fn % 26);
-		LOGP(DRLCMAC, LOGL_INFO, "%s TX: START Immediate "
-			"Assignment Uplink (AGCH)\n", tbf_name(tbf));
-		trx_no = tbf->trx->trx_no;
-		ts_no = tbf->first_ts;
-		usf = tbf->m_usf[ts_no];
-		tsc = tbf->tsc();
 	}
 	bitvec *immediate_assignment = bitvec_alloc(22) /* without plen */;
 	bitvec_unhex(immediate_assignment,
 		"2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b2b");
 
-	LOGP(DRLCMAC, LOGL_DEBUG,
-		" - TRX=%d (%d) TS=%d TA=%d TSC=%d TFI=%d USF=%d\n",
-		trx_no, m_bts.trx[trx_no].arfcn, ts_no, ta, tsc,
-		tbf ? tbf->tfi() : -1, usf);
 
-	plen = Encoding::write_immediate_assignment(
-		tbf, immediate_assignment, 0, ra, Fn, ta,
-		m_bts.trx[trx_no].arfcn, ts_no, tsc, usf, 0, sb_fn,
-		m_bts.alpha, m_bts.gamma, -1, burst_type, sb);
+	if (failure)
+		plen = Encoding::write_immediate_assignment_reject(
+			immediate_assignment, ra, Fn,
+			burst_type);
+	else {
+		LOGP(DRLCMAC, LOGL_DEBUG,
+			" - TRX=%d (%d) TS=%d TA=%d TSC=%d TFI=%d USF=%d\n",
+			trx_no, m_bts.trx[trx_no].arfcn, ts_no, ta, tsc,
+			tbf ? tbf->tfi() : -1, usf);
+
+		plen = Encoding::write_immediate_assignment(
+			tbf, immediate_assignment, 0, ra, Fn, ta,
+			m_bts.trx[trx_no].arfcn, ts_no, tsc, usf, 0, sb_fn,
+			m_bts.alpha, m_bts.gamma, -1, burst_type, sb);
+	}
 
 	if (plen >= 0)
 		pcu_l1if_tx_agch(immediate_assignment, plen);
 
 	bitvec_free(immediate_assignment);
 
-	return 0;
+	return rc;
 }
 
 uint8_t BTS::is_single_block(uint16_t ra, enum ph_burst_type burst_type,
diff --git a/src/encoding.cpp b/src/encoding.cpp
index fb80eeb..ca72b0f 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -242,6 +242,84 @@ static int write_ia_rest_egprs_uplink(
 }
 
 /*
+ * Immediate assignment reject, sent on the CCCH/AGCH
+ * see GSM 44.018, 9.1.20 + 10.5.2.30
+ */
+int Encoding::write_immediate_assignment_reject(
+	bitvec *dest, uint16_t ra,
+	uint32_t ref_fn,
+	enum ph_burst_type burst_type)
+{
+	unsigned wp = 0;
+	int plen;
+	int i;
+
+	bitvec_write_field(dest, wp, 0x0, 4);  // Skip Indicator
+	bitvec_write_field(dest, wp, 0x6, 4);  // Protocol Discriminator
+	bitvec_write_field(dest, wp, 0x3A, 8); // Immediate Assign Message Type
+
+	// feature indicator
+	bitvec_write_field(dest, wp, 0x0, 1);      // spare
+	bitvec_write_field(dest, wp, 0x0, 1);      // spare
+	bitvec_write_field(dest, wp, 0x0, 1);      // no cs
+	bitvec_write_field(dest, wp, 0x1, 1);      // implicit detach for PS
+
+	bitvec_write_field(dest, wp, 0x0, 4); // Page Mode
+	/*
+	 * 9.1.20.2 of 44.018 version 11.7.0 Release 11
+	 * Filling of the message
+	 * If necessary the request reference information element and the
+	 * wait indication information element should be duplicated to
+	 * fill the message.
+	 * TODO: group rejection for multiple MS
+	*/
+	for (i = 0; i < 4; i++) {
+		//10.5.2.30 Request Reference
+		if (((burst_type == GSM_L1_BURST_TYPE_ACCESS_1) ||
+			(burst_type == GSM_L1_BURST_TYPE_ACCESS_2))) {
+			//9.1.20.2a of 44.018 version 11.7.0 Release 11
+			bitvec_write_field(dest, wp, 0x7f, 8);  /* RACH value */
+		} else {
+			bitvec_write_field(dest, wp, ra, 8);	/* RACH value */
+		}
+
+		bitvec_write_field(dest, wp,
+					(ref_fn / (26 * 51)) % 32, 5); // T1'
+		bitvec_write_field(dest, wp, ref_fn % 51, 6);          // T3
+		bitvec_write_field(dest, wp, ref_fn % 26, 5);          // T2
+
+		/* TODO: Make it configurable */
+		bitvec_write_field(dest, wp, 20, 8); //Wait Indication 1
+	}
+
+	plen = wp / 8;
+
+	if ((wp % 8)) {
+		LOGP(DRLCMACUL, LOGL_ERROR, "Length of IMM.ASS.Rej without"
+			"rest octets is not multiple of 8 bits, PLEASE FIX!\n");
+		return -1;
+	}
+
+	// Extended RA
+	else if (((burst_type == GSM_L1_BURST_TYPE_ACCESS_1) ||
+			(burst_type == GSM_L1_BURST_TYPE_ACCESS_2))) {
+		//9.1.20.2a of 44.018 version 11.7.0 Release 11
+		uint8_t extended_ra = 0;
+
+		extended_ra = (ra & 0x1F);
+		bitvec_write_field(dest, wp, 0x1, 1);
+		bitvec_write_field(dest, wp, extended_ra, 5); /* Extended RA */
+	} else {
+		bitvec_write_field(dest, wp, 0x0, 1);
+	}
+	bitvec_write_field(dest, wp, 0x0, 1);
+	bitvec_write_field(dest, wp, 0x0, 1);
+	bitvec_write_field(dest, wp, 0x0, 1);
+
+	return plen;
+}
+
+/*
  * Immediate assignment, sent on the CCCH/AGCH
  * see GSM 04.08, 9.1.18 and GSM 44.018, 9.1.18 + 10.5.2.16
  */
diff --git a/src/encoding.h b/src/encoding.h
index 69f8cdc..79dc32d 100644
--- a/src/encoding.h
+++ b/src/encoding.h
@@ -52,6 +52,12 @@ public:
 				GSM_L1_BURST_TYPE_ACCESS_0,
 			uint8_t sb = 1);
 
+	static int write_immediate_assignment_reject(
+			bitvec *dest, uint16_t ra,
+			uint32_t ref_fn,
+			enum ph_burst_type burst_type
+		);
+
 	static void write_packet_uplink_assignment(
 			struct gprs_rlcmac_bts *bts,
 			bitvec * dest, uint8_t old_tfi,