l1/facch9: Add FACCH9 channel coding support

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

2 files changed, 147 insertions, 1 deletions

diff --git a/src/l1/Makefile.am b/src/l1/Makefile.am
index 3ef01a3..244a369 100644
--- a/src/l1/Makefile.am
+++ b/src/l1/Makefile.am
@@ -6,4 +6,4 @@ noinst_LIBRARIES = libgmr1-l1.a
 
 libgmr1_l1_a_SOURCES = \
 	conv.c crc.c interleave.c punct.c scramb.c \
-	a5.c bcch.c ccch.c rach.c facch3.c tch3.c
+	a5.c bcch.c ccch.c rach.c facch3.c facch9.c tch3.c
diff --git a/src/l1/facch9.c b/src/l1/facch9.c
new file mode 100644
index 0000000..4903c0e
--- /dev/null
+++ b/src/l1/facch9.c
@@ -0,0 +1,146 @@
+/* GMR-1 FACCH9 channel coding */
+/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.11 */
+
+/* (C) 2012 by Sylvain Munaut <tnt@246tNt.com>
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*! \addtogroup facch9
+ *  @{
+ */
+
+/*! \file l1/facch9.c
+ *  \brief Osmocom GMR-1 FACCH9 channel coding implementation
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/conv.h>
+#include <osmocom/core/crc16gen.h>
+
+#include <osmocom/gmr1/l1/conv.h>
+#include <osmocom/gmr1/l1/crc.h>
+#include <osmocom/gmr1/l1/interleave.h>
+#include <osmocom/gmr1/l1/scramb.h>
+
+
+static struct osmo_conv_code gmr1_conv_facch9;
+
+static void __attribute__ ((constructor))
+gmr1_facch9_init(void)
+{
+	/* Init convolutional coder */
+	memcpy(&gmr1_conv_facch9, &gmr1_conv_12, sizeof(struct osmo_conv_code));
+	gmr1_conv_facch9.len = 316;
+}
+
+
+/*! \brief Stateless GMR-1 FACCH9 channel coder
+ *  \param[out] bits_e 662 encoded bits of one NT9 burst
+ *  \param[in] l2 L2 packet data (38 bytes, last nibble unused)
+ *  \param[in] bits_sacch 10 saach bits to be multiplexed
+ *  \param[in] bits_status 4 status bits to be multiplexed
+ *  \param[in] ciph 658 bits of cipher stream (can be NULL)
+ */
+void
+gmr1_facch9_encode(ubit_t *bits_e, const uint8_t *l2,
+                   const ubit_t *bits_sacch, const ubit_t *bits_status,
+                   const ubit_t *ciph)
+{
+	ubit_t bits_u[316];
+	ubit_t bits_c[640];
+	ubit_t bits_epp_x[648];
+	ubit_t bits_my[658];
+	int i;
+
+	osmo_pbit2ubit_ext(bits_u, 0, l2, 0, 300, 1);
+	osmo_crc16gen_set_bits(&gmr1_crc16, bits_u, 300, bits_u+300);
+
+	osmo_conv_encode(&gmr1_conv_facch9, bits_u, bits_c);
+
+	memset(bits_epp_x, 0, 4);
+	memset(bits_epp_x+644, 0, 4);
+	gmr1_interleave_intra(bits_epp_x+4, bits_c, 80);
+
+	gmr1_scramble_ubit(bits_epp_x, bits_epp_x, 648);
+
+	memcpy(bits_my,    bits_epp_x,     52);
+	memcpy(bits_my+52, bits_sacch,     10);
+	memcpy(bits_my+62, bits_epp_x+52, 596);
+
+	if (ciph) {
+		for (i=0; i<658; i++)
+			bits_my[i] ^= ciph[i];
+	}
+
+	memcpy(bits_e,    bits_my,      52);
+	memcpy(bits_e+52, bits_status,   4);
+	memcpy(bits_e+56, bits_my+52,  606);
+}
+
+/*! \brief Stateless GMR-1 FACCH9 channel decoder
+ *  \param[out] l2 L2 packet data (38 bytes, last nibble unused)
+ *  \param[out] bits_sacch 10 saach bits demultiplexed
+ *  \param[out] bits_status 4 status bits demultiplexed
+ *  \param[in] bits_e 662 encoded bits of one NT9 burst
+ *  \param[in] ciph 658 bits of cipher stream (can be NULL)
+ *  \param[out] conv_rv Return of the convolutional decode (can be NULL)
+ *  \return 0 if CRC check pass, any other value for fail.
+ */
+
+int
+gmr1_facch9_decode(uint8_t *l2, sbit_t *bits_sacch, sbit_t *bits_status,
+                   const sbit_t *bits_e, const ubit_t *ciph, int *conv_rv)
+{
+	sbit_t bits_my[658];
+	sbit_t bits_epp_x[648];
+	sbit_t bits_c[640];
+	ubit_t bits_u[316];
+	int i, rv;
+
+	memcpy(bits_my,     bits_e,     52);
+	memcpy(bits_status, bits_e+52,   4);
+	memcpy(bits_my+52,  bits_e+56, 606);
+
+	if (ciph) {
+		for (i=0; i<658; i++)
+			if (ciph[i])
+				bits_my[i] *= -1;
+	}
+
+	memcpy(bits_epp_x,    bits_my,     52);
+	memcpy(bits_sacch,    bits_my+52,  10);
+	memcpy(bits_epp_x+52, bits_my+62, 596);
+
+	gmr1_scramble_sbit(bits_epp_x, bits_epp_x, 648);
+
+	gmr1_deinterleave_intra(bits_c, bits_epp_x+4, 80);
+
+	rv = osmo_conv_decode(&gmr1_conv_facch9, bits_c, bits_u);
+	if (conv_rv)
+		*conv_rv = rv;
+
+	rv = osmo_crc16gen_check_bits(&gmr1_crc16, bits_u, 300, bits_u+300);
+
+	l2[38] = 0; /* upper nibble won't be written */
+	osmo_ubit2pbit_ext(l2, 0, bits_u, 0, 300, 1);
+
+	return rv;
+}
+
+/*! @} */