Set DTX in Cell Options

* rename field of struct gsm48_cell_options to better match the spec
* add comments with spec references
* add function for setting DTX in cell options struct
* add necessary enum type

Change-Id: I5a8924f57669c951b2e51b663d95f1d360062a54
Reviewed-on: https://gerrit.osmocom.org/39
Reviewed-by: Harald Welte <laforge@gnumonks.org>
Tested-by: Jenkins Builder

3 files changed, 61 insertions, 2 deletions

diff --git a/include/osmocom/gsm/protocol/gsm_04_08.h b/include/osmocom/gsm/protocol/gsm_04_08.h
index 3282bc16..4800b48b 100644
--- a/include/osmocom/gsm/protocol/gsm_04_08.h
+++ b/include/osmocom/gsm/protocol/gsm_04_08.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <stdint.h>
+#include <stdbool.h>
 
 #include <osmocom/core/utils.h>
 
@@ -469,11 +470,20 @@ struct gsm48_control_channel_descr {
 	uint8_t t3212;
 } __attribute__ ((packed));
 
+enum gsm48_dtx_mode {
+	GSM48_DTX_MAY_BE_USED,
+	GSM48_DTX_SHALL_BE_USED,
+	GSM48_DTX_SHALL_NOT_BE_USED
+};
+
+/* Cell Options for SI6, SACCH (10.5.2.3a.2) or SI3, BCCH (Table 10.5.2.3.1),
+   3GPP TS 44.018 */
 struct gsm48_cell_options {
 	uint8_t radio_link_timeout:4,
 		 dtx:2,
 		 pwrc:1,
-		 spare:1;
+	/* either DN-IND or top bit of DTX IND */
+		 d:1;
 } __attribute__ ((packed));
 
 /* Section 9.2.9 CM service request */
@@ -827,6 +837,9 @@ static inline uint8_t gsm48_hdr_msg_type_r99(const struct gsm48_hdr *hdr)
 	}
 }
 
+void gsm48_set_dtx(struct gsm48_cell_options *op, enum gsm48_dtx_mode full,
+		   enum gsm48_dtx_mode half, bool is_bcch);
+
 #define gsm48_hdr_msg_type gsm48_hdr_msg_type_r99
 
 /* Section 10.4 */
diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index ab626050..8a46f769 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -25,7 +25,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <string.h>
-
+#include <stdbool.h>
 #include <arpa/inet.h>
 
 #include <osmocom/core/utils.h>
@@ -358,6 +358,50 @@ int gsm48_decode_lai(struct gsm48_loc_area_id *lai, uint16_t *mcc,
 	return 0;
 }
 
+/*! \brief Set DTX mode in Cell Options IE (3GPP TS 44.018)
+ *  \param[in] op Cell Options structure in which DTX parameters will be set
+ *  \param[in] full Mode for full-rate channels
+ *  \param[in] half Mode for half-rate channels
+ *  \param[in] is_bcch Indicates if we should use 10.5.2.3.1 instead of
+ *             10.5.2.3a.2
+ *
+ * There is no space for separate DTX settings for Full and Half rate channels
+ * in BCCH - in this case full setting is used for both and half parameter is
+ * ignored.
+ */
+void gsm48_set_dtx(struct gsm48_cell_options *op, enum gsm48_dtx_mode full,
+		   enum gsm48_dtx_mode half, bool is_bcch)
+{
+	if (is_bcch) {
+		switch (full) {
+		case GSM48_DTX_MAY_BE_USED:
+			op->dtx = 0;
+			return;
+		case GSM48_DTX_SHALL_BE_USED:
+			op->dtx = 1;
+			return;
+		case GSM48_DTX_SHALL_NOT_BE_USED:
+			op->dtx = 2;
+			return;
+		}
+	} else {
+		switch (full) {
+		case GSM48_DTX_MAY_BE_USED:
+			op->dtx = (half == GSM48_DTX_SHALL_BE_USED) ? 3 : 0;
+			op->d =   (half == GSM48_DTX_SHALL_NOT_BE_USED) ? 0 : 1;
+			return;
+		case GSM48_DTX_SHALL_BE_USED:
+			op->dtx = (half == GSM48_DTX_MAY_BE_USED) ? 3 : 1;
+			op->d =   (half == GSM48_DTX_SHALL_BE_USED) ? 1 : 0;
+			return;
+		case GSM48_DTX_SHALL_NOT_BE_USED:
+			op->dtx = 2;
+			op->d =   (half == GSM48_DTX_SHALL_BE_USED) ? 1 : 0;
+			return;
+		}
+	}
+}
+
 int gsm48_generate_mid_from_tmsi(uint8_t *buf, uint32_t tmsi)
 {
 	uint32_t tmsi_be = htonl(tmsi);
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index e0d9dcbd..834e5d66 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -162,6 +162,8 @@ gsm48_mm_att_tlvdef;
 gsm48_number_of_paging_subchannels;
 gsm48_parse_ra;
 gsm48_rr_att_tlvdef;
+gsm48_set_dtx;
+gsm48_dtx_mode;
 gsm48_mi_type_name;
 gsm48_mcc_mnc_to_bcd;
 gsm48_mcc_mnc_from_bcd;