gsm: TS 44.021 modified V.110 frame encoding/decoding support
3GPP TS 44.021 specifies the format for modified V.110 frames as used
on the GSM air (radio) interface. Implement encoders and decoders for
this modified V.110 format.
Related: OS#1572
Change-Id: I60a2f2690459359437df20cf4da9043fa7c3ad11
diff --git a/src/gsm/gsm44021.c b/src/gsm/gsm44021.c
new file mode 100644
index 0000000..5e9d5ab
--- /dev/null
+++ b/src/gsm/gsm44021.c
@@ -0,0 +1,303 @@
+/*************************************************************************
+ * GSM CSD modified V.110 frame decoding/encoding (ubits <-> struct with D/S/X/E bits)
+ *************************************************************************/
+
+/* (C) 2022 by Harald Welte <laforge@osmocom.org>
+ *
+ * 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.
+ */
+
+#include <errno.h>
+#include <osmocom/core/bits.h>
+#include <osmocom/isdn/v110.h>
+
+/*! Decode a 60-bit GSM 12kbit/s CSD frame present as 60 ubits into a struct osmo_v110_decoded_frame.
+ * \param[out] caller-allocated output data structure, filled by this function
+ * \param[in] ra_bits One V.110 frame as 60 unpacked bits. */
+int osmo_csd_12k_6k_decode_frame(struct osmo_v110_decoded_frame *fr, const ubit_t *ra_bits, size_t n_bits)
+{
+ /* 3GPP TS 44.021 Section 8.1.2 / 8.1.3
+ D1 D2 D3 D4 D5 D6 S1
+ D7 D8 D9 D10 D11 D12 X
+ D13 D14 D15 D16 D17 D18 S3
+ D19 D20 D21 D22 D23 D24 S4
+ E4 E5 E6 E7 D25 D26 D27
+ D28 D29 D30 S6 D31 D32 D33
+ D34 D35 D36 X D37 D38 D39
+ D40 D41 D42 S8 D43 D44 D45
+ D46 D47 D48 S9 */
+
+ if (n_bits < 60)
+ return -EINVAL;
+
+ /* X1 .. X2 */
+ fr->x_bits[0] = ra_bits[1 * 7 + 6];
+ fr->x_bits[1] = ra_bits[6 * 7 + 3];
+
+ /* S1, S3, S4, S6, S8, S9 */
+ fr->s_bits[0] = ra_bits[0 * 7 + 6];
+ fr->s_bits[2] = ra_bits[2 * 7 + 6];
+ fr->s_bits[3] = ra_bits[3 * 7 + 6];
+ fr->s_bits[5] = ra_bits[5 * 7 + 3];
+ fr->s_bits[7] = ra_bits[7 * 7 + 3];
+ fr->s_bits[8] = ra_bits[8 * 7 + 3];
+
+ /* E1 .. E3 must be set by out-of-band knowledge! */
+
+ /* E4 .. E7 */
+ memcpy(fr->e_bits+3, ra_bits + 4 * 7 + 0, 4);
+
+ /* D-bits */
+ memcpy(fr->d_bits + 0 * 6 + 0, ra_bits + 0 * 7 + 0, 6);
+ memcpy(fr->d_bits + 1 * 6 + 0, ra_bits + 1 * 7 + 0, 6);
+ memcpy(fr->d_bits + 2 * 6 + 0, ra_bits + 2 * 7 + 0, 6);
+ memcpy(fr->d_bits + 3 * 6 + 0, ra_bits + 3 * 7 + 0, 6);
+ memcpy(fr->d_bits + 4 * 6 + 0, ra_bits + 4 * 7 + 4, 3);
+ memcpy(fr->d_bits + 4 * 6 + 3, ra_bits + 5 * 7 + 0, 3);
+ memcpy(fr->d_bits + 5 * 6 + 0, ra_bits + 5 * 7 + 4, 3);
+ memcpy(fr->d_bits + 5 * 6 + 3, ra_bits + 6 * 7 + 0, 3);
+ memcpy(fr->d_bits + 6 * 6 + 0, ra_bits + 6 * 7 + 4, 3);
+ memcpy(fr->d_bits + 6 * 6 + 3, ra_bits + 7 * 7 + 0, 3);
+ memcpy(fr->d_bits + 7 * 6 + 0, ra_bits + 7 * 7 + 4, 3);
+ memcpy(fr->d_bits + 7 * 6 + 3, ra_bits + 8 * 7 + 0, 3);
+
+ return 0;
+}
+
+int osmo_csd_12k_6k_encode_frame(ubit_t *ra_bits, size_t ra_bits_size, const struct osmo_v110_decoded_frame *fr)
+{
+ if (ra_bits_size < 60)
+ return -EINVAL;
+
+ /* X1 .. X2 */
+ ra_bits[1 * 7 + 6] = fr->x_bits[0];
+ ra_bits[6 * 7 + 3] = fr->x_bits[1];
+
+ /* S1, S3, S4, S6, S8, S9 */
+ ra_bits[0 * 7 + 6] = fr->s_bits[0];
+ ra_bits[2 * 7 + 6] = fr->s_bits[2];
+ ra_bits[3 * 7 + 6] = fr->s_bits[3];
+ ra_bits[5 * 7 + 3] = fr->s_bits[5];
+ ra_bits[7 * 7 + 3] = fr->s_bits[7];
+ ra_bits[8 * 7 + 3] = fr->s_bits[8];
+
+ /* E1 .. E3 are dropped */
+
+ /* E4 .. E7 */
+ memcpy(ra_bits + 4 * 7 + 0, fr->e_bits+3, 4);
+
+ /* D-bits */
+ memcpy(ra_bits + 0 * 7 + 0, fr->d_bits + 0 * 6 + 0, 6);
+ memcpy(ra_bits + 1 * 7 + 0, fr->d_bits + 1 * 6 + 0, 6);
+ memcpy(ra_bits + 2 * 7 + 0, fr->d_bits + 2 * 6 + 0, 6);
+ memcpy(ra_bits + 3 * 7 + 0, fr->d_bits + 3 * 6 + 0, 6);
+ memcpy(ra_bits + 4 * 7 + 4, fr->d_bits + 4 * 6 + 0, 3);
+ memcpy(ra_bits + 5 * 7 + 0, fr->d_bits + 4 * 6 + 3, 3);
+ memcpy(ra_bits + 5 * 7 + 4, fr->d_bits + 5 * 6 + 0, 3);
+ memcpy(ra_bits + 6 * 7 + 0, fr->d_bits + 5 * 6 + 3, 3);
+ memcpy(ra_bits + 6 * 7 + 4, fr->d_bits + 6 * 6 + 0, 3);
+ memcpy(ra_bits + 7 * 7 + 0, fr->d_bits + 6 * 6 + 3, 3);
+ memcpy(ra_bits + 7 * 7 + 4, fr->d_bits + 7 * 6 + 0, 3);
+ memcpy(ra_bits + 8 * 7 + 0, fr->d_bits + 7 * 6 + 3, 3);
+
+ return 60;
+}
+
+/*! Decode a 36-bit GSM 3k6kbit/s CSD frame present as 36 ubits into a struct osmo_v110_decoded_frame.
+ * \param[out] caller-allocated output data structure, filled by this function
+ * \param[in] ra_bits One V.110 frame as 36 unpacked bits. */
+int osmo_csd_3k6_decode_frame(struct osmo_v110_decoded_frame *fr, const ubit_t *ra_bits, size_t n_bits)
+{
+
+ /* 3GPP TS 44.021 Section 8.1.4
+ D1 D2 D3 S1 D4 D5 D6 X
+ D7 D8 D9 S3 D10 D11 D12 S4
+ E4 E5 E6 E7 D13 D14 D15 S6
+ D16 D17 D18 X D19 D20 D21 S8
+ D22 D23 D24 S9
+ */
+
+ if (n_bits < 36)
+ return -EINVAL;
+
+ /* X1 .. X2 */
+ fr->x_bits[0] = ra_bits[0 * 8 + 7];
+ fr->x_bits[1] = ra_bits[3 * 8 + 3];
+
+ /* S1, S3, S4, S6, S8, S9 */
+ fr->s_bits[0] = ra_bits[0 * 8 + 3];
+ fr->s_bits[2] = ra_bits[1 * 8 + 3];
+ fr->s_bits[3] = ra_bits[1 * 8 + 7];
+ fr->s_bits[5] = ra_bits[2 * 8 + 7];
+ fr->s_bits[7] = ra_bits[3 * 8 + 7];
+ fr->s_bits[8] = ra_bits[4 * 8 + 3];
+
+ /* E1 .. E3 must be set by out-of-band knowledge! */
+
+ /* E4 .. E7 */
+ memcpy(fr->e_bits+3, ra_bits + 2 * 8 + 0, 4);
+
+ /* D-bits */
+ unsigned int d_idx = 0;
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 0]; /* D1 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 0]; /* D1 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 1]; /* D2 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 1]; /* D2 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 2]; /* D3 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 2]; /* D3 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 4]; /* D4 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 4]; /* D4 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 5]; /* D5 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 5]; /* D5 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 6]; /* D6 */
+ fr->d_bits[d_idx++] = ra_bits[0 * 8 + 6]; /* D6 */
+
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 0]; /* D7 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 0]; /* D7 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 1]; /* D8 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 1]; /* D8 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 2]; /* D9 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 2]; /* D9 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 4]; /* D10 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 4]; /* D10 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 5]; /* D11 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 5]; /* D11 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 6]; /* D12 */
+ fr->d_bits[d_idx++] = ra_bits[1 * 8 + 6]; /* D12 */
+
+ fr->d_bits[d_idx++] = ra_bits[2 * 8 + 4]; /* D13 */
+ fr->d_bits[d_idx++] = ra_bits[2 * 8 + 4]; /* D13 */
+ fr->d_bits[d_idx++] = ra_bits[2 * 8 + 5]; /* D14 */
+ fr->d_bits[d_idx++] = ra_bits[2 * 8 + 5]; /* D14 */
+ fr->d_bits[d_idx++] = ra_bits[2 * 8 + 6]; /* D15 */
+ fr->d_bits[d_idx++] = ra_bits[2 * 8 + 6]; /* D15 */
+
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 0]; /* D16 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 0]; /* D16 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 1]; /* D17 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 1]; /* D17 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 2]; /* D18 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 2]; /* D18 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 4]; /* D19 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 4]; /* D19 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 5]; /* D20 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 5]; /* D20 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 6]; /* D21 */
+ fr->d_bits[d_idx++] = ra_bits[3 * 8 + 6]; /* D21 */
+
+ fr->d_bits[d_idx++] = ra_bits[4 * 8 + 0]; /* D22 */
+ fr->d_bits[d_idx++] = ra_bits[4 * 8 + 0]; /* D22 */
+ fr->d_bits[d_idx++] = ra_bits[4 * 8 + 1]; /* D23 */
+ fr->d_bits[d_idx++] = ra_bits[4 * 8 + 1]; /* D23 */
+ fr->d_bits[d_idx++] = ra_bits[4 * 8 + 2]; /* D24 */
+ fr->d_bits[d_idx++] = ra_bits[4 * 8 + 2]; /* D24 */
+
+ OSMO_ASSERT(d_idx == 48);
+
+ return 0;
+}
+
+int osmo_csd_3k6_encode_frame(ubit_t *ra_bits, size_t ra_bits_size, const struct osmo_v110_decoded_frame *fr)
+{
+ if (ra_bits_size < 36)
+ return -EINVAL;
+
+ /* X1 .. X2 */
+ ra_bits[0 * 8 + 7] = fr->x_bits[0];
+ ra_bits[3 * 8 + 3] = fr->x_bits[1];
+
+ /* S1, S3, S4, S6, S8, S9 */
+ ra_bits[0 * 8 + 3] = fr->s_bits[0];
+ ra_bits[1 * 8 + 3] = fr->s_bits[2];
+ ra_bits[1 * 8 + 7] = fr->s_bits[3];
+ ra_bits[2 * 8 + 7] = fr->s_bits[5];
+ ra_bits[3 * 8 + 7] = fr->s_bits[7];
+ ra_bits[4 * 8 + 3] = fr->s_bits[8];
+
+ /* E1 .. E3 are ignored */
+
+ /* E4 .. E7 */
+ memcpy(ra_bits + 2 * 8 + 0, fr->e_bits+3, 4);
+
+ /* D-bits */
+ unsigned int d_idx = 0;
+ ra_bits[0 * 8 + 0] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[0 * 8 + 1] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[0 * 8 + 2] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[0 * 8 + 4] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[0 * 8 + 5] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[0 * 8 + 6] = fr->d_bits[d_idx]; d_idx += 2;
+
+ ra_bits[1 * 8 + 0] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[1 * 8 + 1] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[1 * 8 + 2] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[1 * 8 + 4] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[1 * 8 + 5] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[1 * 8 + 6] = fr->d_bits[d_idx]; d_idx += 2;
+
+ ra_bits[2 * 8 + 4] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[2 * 8 + 5] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[2 * 8 + 6] = fr->d_bits[d_idx]; d_idx += 2;
+
+ ra_bits[3 * 8 + 0] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[3 * 8 + 1] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[3 * 8 + 2] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[3 * 8 + 4] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[3 * 8 + 5] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[3 * 8 + 6] = fr->d_bits[d_idx]; d_idx += 2;
+
+ ra_bits[4 * 8 + 0] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[4 * 8 + 1] = fr->d_bits[d_idx]; d_idx += 2;
+ ra_bits[4 * 8 + 2] = fr->d_bits[d_idx]; d_idx += 2;
+
+ OSMO_ASSERT(d_idx == 48);
+
+ return 36;
+}
+
+/*! Print a encoded "CSD modififed V.110" frame in the same table-like structure as the spec.
+ * \param outf output FILE stream to which to dump
+ * \param[in] fr unpacked bits to dump
+ * \param[in] in_len length of unpacked bits available at fr. */
+void osmo_csd_ubit_dump(FILE *outf, const ubit_t *fr, size_t in_len)
+{
+ switch (in_len) {
+ case 60:
+ for (unsigned int septet = 0; septet < 9; septet++) {
+ if (septet < 8) {
+ fprintf(outf, "%d\t%d\t%d\t%d\t%d\t%d\t%d\n", fr[septet * 7 + 0],
+ fr[septet * 7 + 1], fr[septet * 7 + 2], fr[septet * 7 + 3],
+ fr[septet * 7 + 4], fr[septet * 7 + 5], fr[septet*7 + 6]);
+ } else {
+ fprintf(outf, "%d\t%d\t%d\t%d\n", fr[septet * 7 + 0],
+ fr[septet * 7 + 1], fr[septet * 7 + 2], fr[septet * 7 + 3]);
+ }
+ }
+ break;
+ case 36:
+ for (unsigned int octet = 0; octet < 5; octet++) {
+ if (octet < 4) {
+ fprintf(outf, "%d\t%d\t%d\t%d\t%d\t%d\t%d\t%d\n",
+ fr[octet * 8 + 0], fr[octet * 8 + 1], fr[octet * 8 + 2],
+ fr[octet * 8 + 3], fr[octet * 8 + 4], fr[octet * 8 + 5],
+ fr[octet * 8 + 6], fr[octet * 8 + 7]);
+ } else {
+ fprintf(outf, "%d\t%d\t%d\t%d\n", fr[octet * 8 + 0],
+ fr[octet * 8 + 1], fr[octet * 8 + 2], fr[octet * 8 + 3]);
+ }
+ }
+ break;
+ default:
+ fprintf(outf, "invalid input data length: %zu\n", in_len);
+ }
+}