add gsm48_number_of_paging_subchannels() function

(from openbsc's rsl_number_of_paging_subchannels)

1 files changed, 13 insertions, 0 deletions

diff --git a/src/gsm/gsm48.c b/src/gsm/gsm48.c
index d0345892..4645af4d 100644
--- a/src/gsm/gsm48.c
+++ b/src/gsm/gsm48.c
@@ -33,6 +33,7 @@
 #include <osmocom/gsm/gsm48.h>
 
 #include <osmocom/gsm/protocol/gsm_04_08.h>
+#include <osmocom/gsm/protocol/gsm_08_58.h>
 
 const struct tlv_definition gsm48_att_tlvdef = {
 	.def = {
@@ -413,3 +414,15 @@ int gsm48_construct_ra(uint8_t *buf, const struct gprs_ra_id *raid)
 
 	return 6;
 }
+
+/* From Table 10.5.33 of GSM 04.08 */
+int gsm48_number_of_paging_subchannels(struct gsm48_control_channel_descr *chan_desc)
+{
+	if (chan_desc->ccch_conf == RSL_BCCH_CCCH_CONF_1_C) {
+		return OSMO_MAX(1, (3 - chan_desc->bs_ag_blks_res))
+			* (chan_desc->bs_pa_mfrms + 2);
+	} else {
+		return (9 - chan_desc->bs_ag_blks_res)
+			* (chan_desc->bs_pa_mfrms + 2);
+	}
+}