PTCCH: implement basic message codec and API

Change-Id: Id79e95aafdde4a71977c64385fce48b729a51ca9
Related: OS#1545

3 files changed, 54 insertions, 0 deletions

diff --git a/src/bts.cpp b/src/bts.cpp
index a9ff5536..24666af0 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -252,6 +252,7 @@ BTS::BTS()
 
 		for (size_t ts_no = 0; ts_no < ARRAY_SIZE(trx->pdch); ++ts_no) {
 			struct gprs_rlcmac_pdch *pdch = &trx->pdch[ts_no];
+			pdch->init_ptcch_msg();
 			pdch->ts_no = ts_no;
 			pdch->trx = trx;
 		}
diff --git a/src/pdch.cpp b/src/pdch.cpp
index e4b25e1b..beb2c13b 100644
--- a/src/pdch.cpp
+++ b/src/pdch.cpp
@@ -48,6 +48,7 @@ extern "C" {
 }
 
 #include <errno.h>
+#include <stdlib.h>
 #include <arpa/inet.h>
 
 extern void *tall_pcu_ctx;
@@ -961,3 +962,37 @@ inline gprs_rlcmac_bts *gprs_rlcmac_pdch::bts_data() const
 {
 	return trx->bts->bts_data();
 }
+
+/* PTCCH (Packet Timing Advance Control Channel) */
+void gprs_rlcmac_pdch::init_ptcch_msg(void)
+{
+	memset(ptcch_msg, PTCCH_TAI_FREE, PTCCH_TAI_NUM);
+	memset(ptcch_msg + PTCCH_TAI_NUM, PTCCH_PADDING, 7);
+}
+
+uint8_t gprs_rlcmac_pdch::reserve_tai(uint8_t ta)
+{
+	uint8_t tai;
+
+	for (tai = 0; tai < PTCCH_TAI_NUM; tai++) {
+		if (ptcch_msg[tai] == PTCCH_TAI_FREE) {
+			ptcch_msg[tai] = ta;
+			return tai;
+		}
+	}
+
+	/* Special case: no free TAI available */
+	return PTCCH_TAI_FREE;
+}
+
+void gprs_rlcmac_pdch::release_tai(uint8_t tai)
+{
+	OSMO_ASSERT(tai < PTCCH_TAI_NUM);
+	ptcch_msg[tai] = PTCCH_TAI_FREE;
+}
+
+void gprs_rlcmac_pdch::update_ta(uint8_t tai, uint8_t ta)
+{
+	OSMO_ASSERT(tai < PTCCH_TAI_NUM);
+	ptcch_msg[tai] = ta;
+}
diff --git a/src/pdch.h b/src/pdch.h
index 30150233..d55f58e1 100644
--- a/src/pdch.h
+++ b/src/pdch.h
@@ -35,6 +35,11 @@ extern "C" {
 
 #include <stdint.h>
 
+/* PTCCH (Packet Timing Advance Control Channel) */
+#define PTCCH_TAI_FREE		0x7f	/*!< Special value for unused TA Indexes */
+#define PTCCH_TAI_NUM		16	/*!< Number of PTCCH/U slots and thus TA Indexes */
+#define PTCCH_PADDING		0x2b	/*!< PTCCH/D messages need to be padded to 23 octets */
+
 /*
  * PDCH instance
  */
@@ -88,6 +93,19 @@ struct gprs_rlcmac_pdch {
 	struct llist_head paging_list; /* list of paging messages */
 	uint32_t last_rts_fn; /* store last frame number of RTS */
 
+	/* PTCCH (Packet Timing Advance Control Channel) */
+	uint8_t ptcch_msg[GSM_MACBLOCK_LEN]; /* 'ready to use' PTCCH/D message */
+#ifdef __cplusplus
+	/* Initialize the PTCCH/D message */
+	void init_ptcch_msg(void);
+	/* Obtain an unused TA Index for a TBF */
+	uint8_t reserve_tai(uint8_t ta);
+	/* Mark a given TA Index as free, so it can be used again */
+	void release_tai(uint8_t tai);
+	/* Update the actual Timing Advance value for a given TA Index */
+	void update_ta(uint8_t tai, uint8_t ta);
+#endif
+
 	/* back pointers */
 	struct gprs_rlcmac_trx *trx;
 	uint8_t ts_no;