trxcon/scheduler: introduce TCH/H TDMA frame mapping helpres

Unlike xCCH, TCH/H channels are using block diagonal interleaving,
so every single burst carries 57 bits of one traffic frame, and 57
bits of another one. Moreover, unlike TCH/F where both traffic
and FACCH/F frames are interleaved over 8 bursts, a FACCH/H is
interleaved over 6 bursts, while a traffic frame is interleaved
over 4 bursts.

This is why a TCH/H burst transmission can't be initiated on
an arbitrary TDMA frame number. It shall be aligned as of
stated in GSM 05.02, clause 7, table 1.

This change introduces two basic functions:

  - sched_tchh_block_map_fn - checks if a TCH/H block transmission
    can be initiated / finished on a given frame number
    and a given channel type;

  - sched_tchh_block_dl_first_fn - calculates TDMA frame number of
    the first burst using given frame number of the last burst;

and some auxiliary wrappers to simplify the usage of
sched_tchh_block_map_fn().

Change-Id: Iaf4cb33f1b79df23f8a90c8b14ebe0cd9907fbb9

5 files changed, 207 insertions, 16 deletions

diff --git a/src/host/trxcon/Makefile.am b/src/host/trxcon/Makefile.am
index c9cc170a..7095cb59 100644
--- a/src/host/trxcon/Makefile.am
+++ b/src/host/trxcon/Makefile.am
@@ -35,6 +35,7 @@ trxcon_SOURCES += \
 	sched_lchan_desc.c \
 	sched_lchan_xcch.c \
 	sched_lchan_tchf.c \
+	sched_lchan_tchh.c \
 	sched_lchan_rach.c \
 	sched_lchan_sch.c \
 	sched_mframe.c \
diff --git a/src/host/trxcon/sched_lchan_tchh.c b/src/host/trxcon/sched_lchan_tchh.c
new file mode 100644
index 00000000..316f995b
--- /dev/null
+++ b/src/host/trxcon/sched_lchan_tchh.c
@@ -0,0 +1,183 @@
+/*
+ * OsmocomBB <-> SDR connection bridge
+ * TDMA scheduler: handlers for DL / UL bursts on logical channels
+ *
+ * (C) 2018 by Vadim Yanitskiy <axilirator@gmail.com>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <errno.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+#include "scheduler.h"
+#include "sched_trx.h"
+
+static const uint8_t tch_h0_traffic_block_map[3][4] = {
+	/* B0(0,2,4,6), B1(4,6,8,10), B2(8,10,0,2) */
+	{ 0, 2, 4, 6 },
+	{ 4, 6, 8, 10 },
+	{ 8, 10, 0, 2 },
+};
+
+static const uint8_t tch_h1_traffic_block_map[3][4] = {
+	/* B0(1,3,5,7), B1(5,7,9,11), B2(9,11,1,3) */
+	{ 1, 3, 5, 7 },
+	{ 5, 7, 9, 11 },
+	{ 9, 11, 1, 3 },
+};
+
+static const uint8_t tch_h0_dl_facch_block_map[3][6] = {
+	/* B0(4,6,8,10,13,15), B1(13,15,17,19,21,23), B2(21,23,0,2,4,6) */
+	{ 4, 6, 8, 10, 13, 15 },
+	{ 13, 15, 17, 19, 21, 23 },
+	{ 21, 23, 0, 2, 4, 6 },
+};
+
+static const uint8_t tch_h0_ul_facch_block_map[3][6] = {
+	/* B0(0,2,4,6,8,10), B1(8,10,13,15,17,19), B2(17,19,21,23,0,2) */
+	{ 0, 2, 4, 6, 8, 10 },
+	{ 8, 10, 13, 15, 17, 19 },
+	{ 17, 19, 21, 23, 0, 2 },
+};
+
+static const uint8_t tch_h1_dl_facch_block_map[3][6] = {
+	/* B0(5,7,9,11,14,16), B1(14,16,18,20,22,24), B2(22,24,1,3,5,7) */
+	{ 5, 7, 9, 11, 14, 16 },
+	{ 14, 16, 18, 20, 22, 24 },
+	{ 22, 24, 1, 3, 5, 7 },
+};
+
+const uint8_t tch_h1_ul_facch_block_map[3][6] = {
+	/* B0(1,3,5,7,9,11), B1(9,11,14,16,18,20), B2(18,20,22,24,1,3) */
+	{ 1, 3, 5, 7, 9, 11 },
+	{ 9, 11, 14, 16, 18, 20 },
+	{ 18, 20, 22, 24, 1, 3 },
+};
+
+/**
+ * Can a TCH/H block transmission be initiated / finished
+ * on a given frame number and a given channel type?
+ *
+ * See GSM 05.02, clause 7, table 1
+ *
+ * @param  chan   channel type (TRXC_TCHH_0 or TRXC_TCHH_1)
+ * @param  fn     the current frame number
+ * @param  ul     Uplink or Downlink?
+ * @param  facch  FACCH/H or traffic?
+ * @param  start  init or end of transmission?
+ * @return        true (yes) or false (no)
+ */
+bool sched_tchh_block_map_fn(enum trx_lchan_type chan,
+	uint32_t fn, bool ul, bool facch, bool start)
+{
+	uint8_t fn_mf;
+	int i = 0;
+
+	/* Just to be sure */
+	OSMO_ASSERT(chan == TRXC_TCHH_0 || chan == TRXC_TCHH_1);
+
+	/* Calculate a modulo */
+	fn_mf = facch ? (fn % 26) : (fn % 13);
+
+#define MAP_GET_POS(map) \
+	(start ? 0 : ARRAY_SIZE(map[i]) - 1)
+
+#define BLOCK_MAP_FN(map) \
+	do { \
+		if (map[i][MAP_GET_POS(map)] == fn_mf) \
+			return true; \
+	} while (++i < ARRAY_SIZE(map))
+
+	/* Choose a proper block map */
+	if (facch) {
+		if (ul) {
+			if (chan == TRXC_TCHH_0)
+				BLOCK_MAP_FN(tch_h0_ul_facch_block_map);
+			else
+				BLOCK_MAP_FN(tch_h1_ul_facch_block_map);
+		} else {
+			if (chan == TRXC_TCHH_0)
+				BLOCK_MAP_FN(tch_h0_dl_facch_block_map);
+			else
+				BLOCK_MAP_FN(tch_h1_dl_facch_block_map);
+		}
+	} else {
+		if (chan == TRXC_TCHH_0)
+			BLOCK_MAP_FN(tch_h0_traffic_block_map);
+		else
+			BLOCK_MAP_FN(tch_h1_traffic_block_map);
+	}
+
+	return false;
+}
+
+/**
+ * Calculates a frame number of the first burst
+ * using given frame number of the last burst.
+ *
+ * See GSM 05.02, clause 7, table 1
+ *
+ * @param  chan      channel type (TRXC_TCHH_0 or TRXC_TCHH_1)
+ * @param  last_fn   frame number of the last burst
+ * @param  facch     FACCH/H or traffic?
+ * @return           either frame number of the first burst,
+ *                   or fn=last_fn if calculation failed
+ */
+uint32_t sched_tchh_block_dl_first_fn(enum trx_lchan_type chan,
+	uint32_t last_fn, bool facch)
+{
+	uint8_t fn_mf, fn_diff;
+	int i = 0;
+
+	/* Just to be sure */
+	OSMO_ASSERT(chan == TRXC_TCHH_0 || chan == TRXC_TCHH_1);
+
+	/* Calculate a modulo */
+	fn_mf = facch ? (last_fn % 26) : (last_fn % 13);
+
+#define BLOCK_FIRST_FN(map) \
+	do { \
+		if (map[i][ARRAY_SIZE(map[i]) - 1] == fn_mf) { \
+			fn_diff = TDMA_FN_DIFF(fn_mf, map[i][0]); \
+			return TDMA_FN_SUB(last_fn, fn_diff); \
+		} \
+	} while (++i < ARRAY_SIZE(map))
+
+	/* Choose a proper block map */
+	if (facch) {
+		if (chan == TRXC_TCHH_0)
+			BLOCK_FIRST_FN(tch_h0_dl_facch_block_map);
+		else
+			BLOCK_FIRST_FN(tch_h1_dl_facch_block_map);
+	} else {
+		if (chan == TRXC_TCHH_0)
+			BLOCK_FIRST_FN(tch_h0_traffic_block_map);
+		else
+			BLOCK_FIRST_FN(tch_h1_traffic_block_map);
+	}
+
+	LOGP(DSCHD, LOGL_ERROR, "Failed to calculate TDMA "
+		"frame number of the first burst of %s block, "
+		"using the current fn=%u\n", facch ?
+			"FACCH/H" : "TCH/H", last_fn);
+
+	/* Couldn't calculate the first fn, return the last */
+	return last_fn;
+}
diff --git a/src/host/trxcon/sched_prim.c b/src/host/trxcon/sched_prim.c
index e663bc3f..6b160d1c 100644
--- a/src/host/trxcon/sched_prim.c
+++ b/src/host/trxcon/sched_prim.c
@@ -248,23 +248,10 @@ static struct trx_ts_prim *prim_dequeue_tch_h(struct llist_head *queue,
 {
 	struct trx_ts_prim *facch;
 	struct trx_ts_prim *tch;
-	bool facch_now = false;
-	uint32_t fn_mf;
+	bool facch_now;
 
-	/* Traffic multiframe period */
-	fn_mf = fn % 26;
-
-	/* FACCH/H0 frame alignment */
-	if (lchan_type == TRXC_TCHH_0)
-		if (fn_mf == 0 || fn_mf == 8 || fn_mf == 17)
-			facch_now = true;
-
-	/* FACCH/H1 frame alignment */
-	if (lchan_type == TRXC_TCHH_1)
-		if (fn_mf == 1 || fn_mf == 9 || fn_mf == 18)
-			facch_now = true;
-
-	/* If FACCH/H is not allowed for a given frame number */
+	/* May we initiate an UL FACCH/H frame transmission now? */
+	facch_now = sched_tchh_facch_start(lchan_type, fn, true);
 	if (!facch_now) /* Just dequeue a TCH/H prim */
 		goto no_facch;
 
diff --git a/src/host/trxcon/sched_trx.h b/src/host/trxcon/sched_trx.h
index 730923b4..2c8b4d8f 100644
--- a/src/host/trxcon/sched_trx.h
+++ b/src/host/trxcon/sched_trx.h
@@ -323,3 +323,19 @@ int sched_send_dt_ind(struct trx_instance *trx, struct trx_ts *ts,
 	int bit_error_count, bool dec_failed, bool traffic);
 int sched_send_dt_conf(struct trx_instance *trx, struct trx_ts *ts,
 	struct trx_lchan_state *lchan, uint32_t fn, bool traffic);
+
+/* Interleaved TCH/H block TDMA frame mapping */
+uint32_t sched_tchh_block_dl_first_fn(enum trx_lchan_type chan,
+	uint32_t last_fn, bool facch);
+bool sched_tchh_block_map_fn(enum trx_lchan_type chan,
+	uint32_t fn, bool ul, bool facch, bool start);
+
+#define sched_tchh_traffic_start(chan, fn, ul) \
+	sched_tchh_block_map_fn(chan, fn, ul, 0, 1)
+#define sched_tchh_traffic_end(chan, fn, ul) \
+	sched_tchh_block_map_fn(chan, fn, ul, 0, 0)
+
+#define sched_tchh_facch_start(chan, fn, ul) \
+	sched_tchh_block_map_fn(chan, fn, ul, 1, 1)
+#define sched_tchh_facch_end(chan, fn, ul) \
+	sched_tchh_block_map_fn(chan, fn, ul, 1, 0)
diff --git a/src/host/trxcon/scheduler.h b/src/host/trxcon/scheduler.h
index fccf7d23..7ab17ab5 100644
--- a/src/host/trxcon/scheduler.h
+++ b/src/host/trxcon/scheduler.h
@@ -17,6 +17,10 @@
 	((a + GSM_HYPERFRAME - b) % GSM_HYPERFRAME)
 #define TDMA_FN_INC(fn) \
 	TDMA_FN_SUM(fn, 1)
+#define TDMA_FN_MIN(a, b) \
+	(a < b ? a : b)
+#define TDMA_FN_DIFF(a, b) \
+	TDMA_FN_MIN(TDMA_FN_SUB(a, b), TDMA_FN_SUB(b, a))
 
 enum tdma_sched_clck_state {
 	SCH_CLCK_STATE_WAIT,