l1sap: Fix expired rach slot counting

The counting of the expired rach slots in l1sap.c is not correctly
implemented. This commit fixes the implementation. The expired
rach slots are now conted correctly according to the configured
channel combination. If a CCCH and SDCCH are combined, only the
frames related to rach slots are counted.

Change-Id: I87f40f5f160a4f6750c4f3d06997fc4f24049303

1 files changed, 56 insertions, 16 deletions

diff --git a/src/common/l1sap.c b/src/common/l1sap.c
index 968237f3..0ce1e4a0 100644
--- a/src/common/l1sap.c
+++ b/src/common/l1sap.c
@@ -352,18 +352,67 @@ static int to_gsmtap(struct gsm_bts_trx *trx, struct osmo_phsap_prim *l1sap)
 	return 0;
 }
 
+/* Calculate the number of RACH slots that expire in a certain GSM frame
+ * See also 3GPP TS 05.02 Clause 7 Table 5 of 9 */
+static unsigned int calc_exprd_rach_frames(struct gsm_bts *bts, uint32_t fn)
+{
+	int rach_frames_expired = 0;
+	uint8_t ccch_conf;
+	struct gsm48_system_information_type_3 *si3;
+	unsigned int blockno;
+
+	si3 = GSM_BTS_SI(bts, SYSINFO_TYPE_3);
+	ccch_conf = si3->control_channel_desc.ccch_conf;
+
+	if (ccch_conf == RSL_BCCH_CCCH_CONF_1_C) {
+		/* It is possible to combine a CCCH with an SDCCH4, in this
+		 * case the CCCH will have to share the available frames with
+		 * the other channel, this results in a limited number of
+		 * available rach slots */
+		blockno = fn % 51;
+		if (blockno == 4 || blockno == 5
+		    || (blockno >= 15 && blockno <= 36) || blockno == 45
+		    || blockno == 46)
+			rach_frames_expired = 1;
+	} else {
+		/* It is possible to have multiple CCCH channels on
+		 * different physical channels (large cells), this
+		 * also multiplies the available/expired RACH channels.
+		 * See also TS 04.08, Chapter 10.5.2.11, table 10.29 */
+		if (ccch_conf == RSL_BCCH_CCCH_CONF_2_NC)
+			rach_frames_expired = 2;
+		if (ccch_conf == RSL_BCCH_CCCH_CONF_3_NC)
+			rach_frames_expired = 3;
+		if (ccch_conf == RSL_BCCH_CCCH_CONF_4_NC)
+			rach_frames_expired = 4;
+		else
+			rach_frames_expired = 1;
+	}
+
+	/* Each Frame has room for 4 RACH slots, since RACH
+	 * slots are short enough to fit into a single radio
+	 * burst, so we need to multiply the final result by 4 */
+	return rach_frames_expired * 4;
+}
+
 /* time information received from bts model */
 static int l1sap_info_time_ind(struct gsm_bts *bts,
-	struct osmo_phsap_prim *l1sap,
-	struct info_time_ind_param *info_time_ind)
+			       struct osmo_phsap_prim *l1sap,
+			       struct info_time_ind_param *info_time_ind)
 {
 	struct gsm_bts_trx *trx;
 	struct gsm_bts_role_bts *btsb = bts->role;
-
-	int frames_expired = info_time_ind->fn - btsb->gsm_time.fn;
+	int frames_expired;
 
 	DEBUGP(DL1P, "MPH_INFO time ind %u\n", info_time_ind->fn);
 
+	/* Calculate and check frame difference */
+	frames_expired = info_time_ind->fn - btsb->gsm_time.fn;
+	if (frames_expired > 1) {
+		LOGP(DL1P, LOGL_ERROR,
+		     "Invalid condition detected: Frame difference is > 1!\n");
+	}
+
 	/* Update our data structures with the current GSM time */
 	gsm_fn2gsmtime(&btsb->gsm_time, info_time_ind->fn);
 
@@ -373,24 +422,15 @@ static int l1sap_info_time_ind(struct gsm_bts *bts,
 	/* check if the measurement period of some lchan has ended
 	 * and pre-compute the respective measurement */
 	llist_for_each_entry(trx, &bts->trx_list, list)
-		trx_meas_check_compute(trx, info_time_ind->fn - 1);
+	    trx_meas_check_compute(trx, info_time_ind->fn - 1);
 
 	/* increment number of RACH slots that have passed by since the
 	 * last time indication */
-	if (trx == bts->c0) {
-		unsigned int num_rach_per_frame;
-		/* 27 / 51 taken from TS 05.01 Figure 3 */
-		if (bts->c0->ts[0].pchan == GSM_PCHAN_CCCH_SDCCH4)
-			num_rach_per_frame = 27;
-		else
-			num_rach_per_frame = 51;
-
-		btsb->load.rach.total += frames_expired * num_rach_per_frame;
-	}
+	btsb->load.rach.total +=
+	    calc_exprd_rach_frames(bts, info_time_ind->fn) * frames_expired;
 
 	return 0;
 }
-
 /* measurement information received from bts model */
 static int l1sap_info_meas_ind(struct gsm_bts_trx *trx,
 	struct osmo_phsap_prim *l1sap,