falconia has uploaded this change for review.
trau: add TW-TS-007 packing and unpacking functions
TW-TS-007 packing and unpacking functions in <osmocom/trau/twts007.h>
are symmetric, as much as feasible, with their CLEARMODE counterparts
in <osmocom/trau/csd_v110.h>, <osmocom/trau/csd_ra2.h> and
<osmocom/trau/csd_raa_prime.h>. This symmetry is intended to aid
implementation of CSD RTP endpoints (TRAU<->RTP functions and IWFs
in the CN) that support both payload formats, and it will also serve
as a building block for dedicated format conversion functions.
Change-Id: Ie81280d2b90f69fbdde9fa968f747a35ea123f79
---
M include/Makefile.am
A include/osmocom/trau/twts007.h
M src/Makefile.am
A src/trau/twts007.c
4 files changed, 150 insertions(+), 1 deletion(-)
git pull ssh://gerrit.osmocom.org:29418/libosmo-abis refs/changes/61/41161/1
diff --git a/include/Makefile.am b/include/Makefile.am
index 862292e..7c00ccc 100644
--- a/include/Makefile.am
+++ b/include/Makefile.am
@@ -33,6 +33,7 @@
osmocom/trau/trau_pcu_ericsson.h \
osmocom/trau/trau_rtp.h \
osmocom/trau/trau_sync.h \
+ osmocom/trau/twts007.h \
$(NULL)
if ENABLE_ORTP
diff --git a/include/osmocom/trau/twts007.h b/include/osmocom/trau/twts007.h
new file mode 100644
index 0000000..f991379
--- /dev/null
+++ b/include/osmocom/trau/twts007.h
@@ -0,0 +1,42 @@
+/*
+ * This header file defines the public API for working with compressed-CSD
+ * RTP format of TW-TS-007:
+ *
+ * https://www.freecalypso.org/specs/tw-ts-007-v010001.txt
+ *
+ * Author: Mychaela N. Falconia <falcon@freecalypso.org>, 2025 - however,
+ * Mother Mychaela's contributions are NOT subject to copyright.
+ * No rights reserved, all rights relinquished.
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <osmocom/core/bits.h>
+
+/* RTP payload lengths for different modes of compressed CSD */
+#define OSMO_CCSD_PL_LEN_4k8 16 /* TW-TS-007 section 7.2 */
+#define OSMO_CCSD_PL_LEN_9k6 32 /* TW-TS-007 section 7.3 */
+#define OSMO_CCSD_PL_LEN_14k4 37 /* TW-TS-007 section 7.4 */
+
+/* low-level CSD frame packing and unpacking functions */
+
+void osmo_ccsd_pack_v110_frame(uint8_t *out_bytes, const ubit_t *bits_63);
+void osmo_ccsd_pack_atrau_frame(uint8_t *out_bytes, const ubit_t *m_bits,
+ const ubit_t *d_bits, ubit_t atrau_c4,
+ ubit_t atrau_c5);
+
+int osmo_ccsd_unpack_v110_frame(ubit_t *bits_63, const uint8_t *ccsd_bytes);
+int osmo_ccsd_unpack_atrau_frame(ubit_t *m_bits, ubit_t *d_bits,
+ ubit_t *atrau_c4, ubit_t *atrau_c5,
+ const uint8_t *ccsd_bytes);
diff --git a/src/Makefile.am b/src/Makefile.am
index 6683d44..b30ebfc 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -60,7 +60,8 @@
trau/trau_frame.c \
trau/trau_pcu_ericsson.c \
trau/trau_sync.c \
- trau/trau_rtp_conv.c
+ trau/trau_rtp_conv.c \
+ trau/twts007.c
if ENABLE_ORTP
libosmotrau_la_SOURCES += trau/osmo_ortp.c
diff --git a/src/trau/twts007.c b/src/trau/twts007.c
new file mode 100644
index 0000000..82614c6
--- /dev/null
+++ b/src/trau/twts007.c
@@ -0,0 +1,105 @@
+/*
+ * This C module contains the implementation of TW-TS-007 compressed CSD
+ * functions defined in <osmocom/trau/twts007.h>.
+ *
+ * Author: Mychaela N. Falconia <falcon@freecalypso.org>, 2025 - however,
+ * Mother Mychaela's contributions are NOT subject to copyright.
+ * No rights reserved, all rights relinquished.
+ *
+ * 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.
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/trau/twts007.h>
+
+/*! Pack V.110 frame content (distilled 63-bit form) into compressed form
+ * of TW-TS-007 section 7.1.
+ * \param[out] out_bytes buffer of size 8 bytes
+ * \param[in] bits_63 63-bit distilled V.110 frame
+ */
+void osmo_ccsd_pack_v110_frame(uint8_t *out_bytes, const ubit_t *bits_63)
+{
+ ubit_t bits_64[64];
+
+ bits_64[0] = 1;
+ memcpy(bits_64 + 1, bits_63, 63);
+ osmo_ubit2pbit(out_bytes, bits_64, 64);
+}
+
+/*! Pack A-TRAU frame content (M-bits, D-bits, C4 and C5 metadata flags)
+ * into compressed form of TW-TS-007 section 7.4.
+ * \param[out] out_bytes buffer of size 37 bytes
+ * \param[in] m_bits 2 M-bits associated with this 20 ms CSD frame
+ * \param[in] d_bits 288 user data bits in this 20 ms CSD frame
+ * \param[in] atrau_c4 value to be put into A-TRAU frame bit C4
+ * \param[in] atrau_c5 value to be put into A-TRAU frame bit C5
+ */
+void osmo_ccsd_pack_atrau_frame(uint8_t *out_bytes, const ubit_t *m_bits,
+ const ubit_t *d_bits, ubit_t atrau_c4,
+ ubit_t atrau_c5)
+{
+ uint8_t head_byte;
+
+ head_byte = 0xB0;
+ head_byte |= (atrau_c4 << 3);
+ head_byte |= (atrau_c5 << 2);
+ head_byte |= (m_bits[0] << 1);
+ head_byte |= (m_bits[1] << 0);
+ out_bytes[0] = head_byte;
+ osmo_ubit2pbit(out_bytes + 1, d_bits, 288);
+}
+
+/*! Extract V.110 frame content (distilled 63-bit form) from compressed form
+ * of TW-TS-007 section 7.1.
+ * \param[out] bits_63 buffer of size 63 ubit_t
+ * \param[in] ccsd_bytes 8-octet compressed V.110 frame of TW-TS-007
+ * section 7.1
+ * \returns 0 if compressed V.110 frame is good; negative if it is invalid
+ */
+int osmo_ccsd_unpack_v110_frame(ubit_t *bits_63, const uint8_t *ccsd_bytes)
+{
+ ubit_t bits_64[64];
+
+ osmo_pbit2ubit(bits_64, ccsd_bytes, 64);
+ if (!bits_64[0])
+ return -EINVAL;
+ memcpy(bits_63, bits_64 + 1, 63);
+ return 0;
+}
+
+/*! Extract A-TRAU frame content from compressed form of TW-TS-007 section 7.4.
+ * \param[out] m_bits caller-provided buffer for 2 M-bits
+ * \param[out] d_bits caller-provided buffer for 288 user data bits
+ * \param[out] atrau_c4 return of A-TRAU frame bit C4 (NULL pointer OK)
+ * \param[out] atrau_c5 return of A-TRAU frame bit C5 (NULL pointer OK)
+ * \param[in] ccsd_bytes 37-octet compressed V.110 frame of TW-TS-007
+ * section 7.4
+ * \returns 0 if compressed A-TRAU frame is good; negative if it is invalid
+ */
+int osmo_ccsd_unpack_atrau_frame(ubit_t *m_bits, ubit_t *d_bits,
+ ubit_t *atrau_c4, ubit_t *atrau_c5,
+ const uint8_t *ccsd_bytes)
+{
+ if ((ccsd_bytes[0] & 0xF0) != 0xB0)
+ return -EINVAL;
+ if (atrau_c4)
+ *atrau_c4 = (ccsd_bytes[0] >> 3) & 1;
+ if (atrau_c5)
+ *atrau_c5 = (ccsd_bytes[0] >> 2) & 1;
+ m_bits[0] = (ccsd_bytes[0] >> 1) & 1;
+ m_bits[1] = (ccsd_bytes[0] >> 0) & 1;
+ osmo_pbit2ubit(d_bits, ccsd_bytes + 1, 288);
+ return 0;
+}
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