dtx: add decoding for AMR-DTX frames

gsm0503_coding contains AMR decoder functions for HR and FR. Those can
only decode AMR payload frames but not amr DTX frames. Lets add
functionality to detect DTX frames. Also lets add decoding for SID_UPDATE
frames as well as error checking for the SID frame recognition patterns.

Related: OS#2978
Change-Id: I2bbdb39ea20461ca08b2e6f1a33532cb55cd5195

1 files changed, 314 insertions, 0 deletions

diff --git a/src/coding/gsm0503_amr_dtx.c b/src/coding/gsm0503_amr_dtx.c
new file mode 100644
index 00000000..724cf091
--- /dev/null
+++ b/src/coding/gsm0503_amr_dtx.c
@@ -0,0 +1,314 @@
+/*
+ * (C) 2020 by sysmocom - s.f.m.c. GmbH, Author: Philipp Maier
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * 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, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <stdlib.h>
+#include <errno.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/conv.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/coding/gsm0503_amr_dtx.h>
+#include <osmocom/coding/gsm0503_parity.h>
+#include <osmocom/gsm/gsm0503.h>
+
+/* See also: 3GPP TS 05.03, chapter 3.10.1.3, 3.10.5.2 Identification marker */
+static const ubit_t id_marker_1[] = { 1, 0, 1, 1, 0, 0, 0, 0, 1 };
+
+/* See also: 3GPP TS 05.03, chapter 3.9.1.3, 3.10.2.2, 3.10.2.2 Identification marker */
+static const ubit_t id_marker_0[] = { 0, 1, 0, 0, 1, 1, 1, 1, 0 };
+
+/* See also: 3GPP TS 05.03, chapter 3.9 Adaptive multi rate speech channel at full rate (TCH/AFS) */
+static const ubit_t codec_mode_1_sid[] = { 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0 };
+static const ubit_t codec_mode_2_sid[] = { 0, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 0 };
+static const ubit_t codec_mode_3_sid[] = { 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1 };
+static const ubit_t codec_mode_4_sid[] = { 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1 };
+
+const struct value_string gsm0503_amr_dtx_frame_names[] = {
+	{ AFS_SID_FIRST,	"AFS_SID_FIRST" },
+	{ AFS_SID_UPDATE,	"AFS_SID_UPDATE" },
+	{ AFS_ONSET,		"AFS_ONSET" },
+	{ AHS_SID_UPDATE,	"AHS_SID_UPDATE" },
+	{ AHS_SID_FIRST_P1,	"AHS_SID_FIRST_P1" },
+	{ AHS_SID_FIRST_P2,	"AHS_SID_FIRST_P2" },
+	{ AHS_ONSET,		"AHS_ONSET" },
+	{ AHS_SID_FIRST_INH,	"AHS_SID_FIRST_INH" },
+	{ AHS_SID_UPDATE_INH,	"AHS_SID_UPDATE_INH" },
+	{ AMR_OTHER,		"NON DTX FRAME (OTHER)" },
+	{ 0, NULL }
+};
+
+static bool detect_afs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, uint8_t offset, uint8_t count,
+				 const ubit_t * id_marker, uint8_t id_marker_len)
+{
+	unsigned int i, k;
+	unsigned int id_bit_nr = 0;
+	int errors = 0;
+	int bits = 0;
+
+	/* Override coded in-band data */
+	ubits += offset;
+
+	/* Check for identification marker bits */
+	for (i = 0; i < count; i++) {
+		for (k = 0; k < 4; k++) {
+			if (id_marker[id_bit_nr % id_marker_len] != *ubits)
+				errors++;
+			id_bit_nr++;
+			ubits++;
+			bits++;
+		}
+
+		/* Jump to the next block of 4 bits */
+		ubits += 4;
+	}
+
+	*n_errors = errors;
+	*n_bits_total = bits;
+
+	/* Tolerate up to 1/8 errornous bits */
+	return *n_errors < *n_bits_total / 8;
+}
+
+static bool detect_ahs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, const ubit_t * id_marker)
+{
+	unsigned int i, k;
+	int errors = 0;
+	int bits = 0;
+
+	/* Override coded in-band data */
+	ubits += 16;
+
+	/* Check first identification marker bits (23*9 bits) */
+	for (i = 0; i < 23; i++) {
+		for (k = 0; k < 9; k++) {
+			if (id_marker[k] != *ubits)
+				errors++;
+			ubits++;
+			bits++;
+		}
+	}
+
+	/* Check remaining identification marker bits (5 bits) */
+	for (k = 0; k < 5; k++) {
+		if (id_marker[k] != *ubits)
+			errors++;
+		ubits++;
+		bits++;
+	}
+
+	*n_errors = errors;
+	*n_bits_total = bits;
+
+	/* Tolerate up to 1/8 errornous bits */
+	return *n_errors < *n_bits_total / 8;
+}
+
+static bool detect_interleaved_ahs_id_marker(int *n_errors, int *n_bits_total, const ubit_t * ubits, uint8_t offset,
+					     uint8_t n_bits, const ubit_t * id_marker, uint8_t id_marker_len)
+{
+	unsigned int i, k;
+	int errors = 0;
+	int bits = 0;
+	uint8_t full_rounds = n_bits / id_marker_len;
+	uint8_t remainder = n_bits % id_marker_len;
+
+	/* Override coded in-band data */
+	ubits += offset;
+
+	/* Check first identification marker bits (23*9 bits) */
+	for (i = 0; i < full_rounds; i++) {
+		for (k = 0; k < id_marker_len; k++) {
+			if (id_marker[k] != *ubits)
+				errors++;
+			ubits += 2;
+			bits++;
+		}
+	}
+
+	/* Check remaining identification marker bits (5 bits) */
+	for (k = 0; k < remainder; k++) {
+		if (id_marker[k] != *ubits)
+			errors++;
+		ubits += 2;
+		bits++;
+	}
+
+	*n_errors = errors;
+	*n_bits_total = bits;
+
+	/* Tolerate up to 1/8 errornous bits */
+	return *n_errors < *n_bits_total / 8;
+}
+
+/* Detect a an FR AMR SID_FIRST frame by its identifcation marker */
+static bool detect_afs_sid_first(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_afs_id_marker(n_errors, n_bits_total, ubits, 32, 53, id_marker_0, 9);
+}
+
+/* Detect an FR AMR SID_FIRST frame by its identification marker */
+static bool detect_afs_sid_update(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_afs_id_marker(n_errors, n_bits_total, ubits, 36, 53, id_marker_0, 9);
+}
+
+/* Detect an FR AMR SID_FIRST frame by its repeating coded inband data */
+static bool detect_afs_onset(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	bool rc;
+
+	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_1_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_2_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_3_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_afs_id_marker(n_errors, n_bits_total, ubits, 4, 57, codec_mode_4_sid, 16);
+	if (rc)
+		return true;
+
+	return false;
+}
+
+/* Detect an HR AMR SID UPDATE frame by its identification marker */
+static bool detect_ahs_sid_update(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_ahs_id_marker(n_errors, n_bits_total, ubits, id_marker_1);
+}
+
+/* Detect an HR AMR SID FIRST (part 1) frame by its identification marker */
+static bool detect_ahs_sid_first_p1(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_ahs_id_marker(n_errors, n_bits_total, ubits, id_marker_0);
+}
+
+/* Detect an HR AMR SID FIRST (part 2) frame by its repeating coded inband data */
+static bool detect_ahs_sid_first_p2(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	bool rc;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_1_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_2_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_3_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 0, 114, codec_mode_4_sid, 16);
+	if (rc)
+		return true;
+
+	return false;
+}
+
+/* Detect an HR AMR ONSET frame by its repeating coded inband data */
+static bool detect_ahs_onset(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	bool rc;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_1_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_2_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_3_sid, 16);
+	if (rc)
+		return true;
+
+	rc = detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 1, 114, codec_mode_4_sid, 16);
+	if (rc)
+		return true;
+
+	return false;
+}
+
+/* Detect an HR AMR SID FIRST INHIBIT frame by its identification marker */
+static bool detect_ahs_sid_first_inh(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 33, 212, id_marker_1, 9);
+}
+
+/* Detect an HR AMR SID UPDATE INHIBIT frame by its identification marker */
+static bool detect_ahs_sid_update_inh(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	return detect_interleaved_ahs_id_marker(n_errors, n_bits_total, ubits, 33, 212, id_marker_0, 9);
+}
+
+/*! Detect FR AMR DTX frame in unmapped, deinterleaved frame bits.
+ *  \param[in] ubits input bits (456 bit).
+ *  \param[out] n_errors number of errornous bits.
+ *  \param[out] n_bits_total number of checked bits.
+ *  \returns dtx frame type. */
+enum gsm0503_amr_dtx_frames gsm0503_detect_afs_dtx_frame(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	if (detect_afs_sid_first(n_errors, n_bits_total, ubits))
+		return AFS_SID_FIRST;
+	if (detect_afs_sid_update(n_errors, n_bits_total, ubits))
+		return AFS_SID_UPDATE;
+	if (detect_afs_onset(n_errors, n_bits_total, ubits))
+		return AFS_ONSET;
+
+	*n_errors = 0;
+	*n_bits_total = 0;
+	return AMR_OTHER;
+}
+
+/*! Detect HR AMR DTX frame in unmapped, deinterleaved frame bits.
+ *  \param[in] ubits input bits (456 bit).
+ *  \param[out] n_errors number of errornous bits.
+ *  \param[out] n_bits_total number of checked bits.
+ *  \returns dtx frame type, */
+enum gsm0503_amr_dtx_frames gsm0503_detect_ahs_dtx_frame(int *n_errors, int *n_bits_total, const ubit_t * ubits)
+{
+	if (detect_ahs_sid_update(n_errors, n_bits_total, ubits))
+		return AHS_SID_UPDATE;
+	if (detect_ahs_sid_first_inh(n_errors, n_bits_total, ubits))
+		return AHS_SID_FIRST_INH;
+	if (detect_ahs_sid_update_inh(n_errors, n_bits_total, ubits))
+		return AHS_SID_UPDATE_INH;
+	if (detect_ahs_sid_first_p1(n_errors, n_bits_total, ubits))
+		return AHS_SID_FIRST_P1;
+	if (detect_ahs_sid_first_p2(n_errors, n_bits_total, ubits))
+		return AHS_SID_FIRST_P2;
+	if (detect_ahs_onset(n_errors, n_bits_total, ubits))
+		return AHS_ONSET;
+
+	*n_errors = 0;
+	*n_bits_total = 0;
+	return AMR_OTHER;
+}