l1/facch3: Add support for FACCH3 channel coding

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

2 files changed, 169 insertions, 1 deletions

diff --git a/src/l1/Makefile.am b/src/l1/Makefile.am
index 4857242..05e068c 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 \
-	bcch.c ccch.c
+	bcch.c ccch.c facch3.c
diff --git a/src/l1/facch3.c b/src/l1/facch3.c
new file mode 100644
index 0000000..d3c847f
--- /dev/null
+++ b/src/l1/facch3.c
@@ -0,0 +1,168 @@
+/* GMR-1 FACCH3 channel coding */
+/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.9 */
+
+/* (C) 2011 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 facch3
+ *  @{
+ */
+
+/*! \file l1/facch3.c
+ *  \brief Osmocom GMR-1 FACCH3 channel coding implementation
+ */
+
+#include <stdint.h>
+#include <string.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_facch3;
+
+static void __attribute__ ((constructor))
+gmr1_facch3_init(void)
+{
+	/* Init convolutional coder */
+	memcpy(&gmr1_conv_facch3, &gmr1_conv_14, sizeof(struct osmo_conv_code));
+	gmr1_conv_facch3.len = 92;
+}
+
+
+/*! \brief Stateless GMR-1 FACCH3 channel coder
+ *  \param[out] bits_e 4*104 encoded bits of 4 bursts
+ *  \param[in] l2 L2 packet data
+ *  \param[in] bits_s 4*8 status bits to be multiplexed
+ *  \param[in] ciph 4*96 bits of cipher stream (can be NULL)
+ *
+ * L2 data is 10 byte long.
+ * bits_s is 32 bits, 8 bits for each of the 4 burts, organized as 4 s_n
+ * followed by 4 s_p, as shown in section 7.3.2.2.
+ * bits_e is a 432 hard bit array to be mapped on 4 bursts.
+ * ciph is the A5 cipher stream to use, 96 bits for each of the 4 burts.
+ */
+void
+gmr1_facch3_encode(ubit_t *bits_e, const uint8_t *l2,
+                   const ubit_t *bits_s, const ubit_t *ciph)
+{
+	ubit_t bits_u[92];
+	ubit_t bits_c[384];
+	ubit_t bits_cp[96*4];
+	ubit_t bits_ep[96*4];
+	ubit_t bits_xmy[96*4];
+	int i, j;
+
+	osmo_pbit2ubit_ext(bits_u, 0, l2, 0, 76, 1);
+	osmo_crc16gen_set_bits(&gmr1_crc16, bits_u, 76, bits_u+76);
+
+	osmo_conv_encode(&gmr1_conv_facch3, bits_u, bits_c);
+
+	for (i=0; i<384; i++)
+		bits_cp[(i&3)*96 + (i>>2)] = bits_c[i];
+
+	for (i=0; i<4; i++)
+	{
+		ubit_t *b_bits_cp  = bits_cp  +  96*i;
+		ubit_t *b_bits_ep  = bits_ep  +  96*i;
+		ubit_t *b_bits_xmy = bits_xmy +  96*i;
+		ubit_t *b_bits_e   = bits_e   + 104*i;
+		const ubit_t *b_bits_s = bits_s + 8*i;
+		const ubit_t *b_ciph = ciph + 96*i;
+
+		gmr1_interleave_intra(b_bits_ep, b_bits_cp, 12);
+		gmr1_scramble_ubit(b_bits_xmy, b_bits_ep, 96);
+
+		if (ciph) {
+			for (j=0; j<96; j++)
+				b_bits_xmy[j] ^= b_ciph[j];
+		}
+
+		memcpy(b_bits_e   , b_bits_xmy,    22);
+		memcpy(b_bits_e+22, b_bits_s,       8);
+		memcpy(b_bits_e+30, b_bits_xmy+22, 74);
+	}
+}
+
+/*! \brief Stateless GMR-1 FACCH3 channel decoder
+ *  \param[out] l2 L2 packet data
+ *  \param[out] bits_s 4*8 status bits de-multiplexed
+ *  \param[in] bits_e 4*104 encoded bits of 4 bursts
+ *  \param[in] ciph 4*96 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.
+ *
+ * L2 data is 10 byte long.
+ * bits_s is 32 bits, 8 bits for each of the 4 burts, organized as 4 s_n
+ * followed by 4 s_p, as shown in section 7.3.2.2.
+ * bits_e is a 424 soft bits array unmapped from 4 bursts.
+ * ciph is the A5 cipher stream to use, 96 bits for each of the 4 burts.
+ */
+int
+gmr1_facch3_decode(uint8_t *l2, ubit_t *bits_s,
+                   const sbit_t *bits_e, const ubit_t *ciph, int *conv_rv)
+{
+	sbit_t bits_xmy[96*4];
+	sbit_t bits_ep[96*4];
+	sbit_t bits_cp[96*4];
+	sbit_t bits_c[384];
+	ubit_t bits_u[92];
+	int rv, i, j;
+
+	for (i=0; i<4; i++)
+	{
+		const sbit_t *b_bits_e = bits_e + 104*i;
+		ubit_t *b_bits_s   = bits_s   +   8*i;
+		sbit_t *b_bits_xmy = bits_xmy +  96*i;
+		sbit_t *b_bits_ep  = bits_ep  +  96*i;
+		sbit_t *b_bits_cp  = bits_cp  +  96*i;
+		const ubit_t *b_ciph = ciph + 96*i;
+
+		for (j=0; j<8; j++)
+			b_bits_s[j] = b_bits_e[22+j] < 0;
+
+		memcpy(b_bits_xmy,    b_bits_e,    22);
+		memcpy(b_bits_xmy+22, b_bits_e+30, 74);
+
+		if (ciph) {
+			for (j=0; j<96; j++)
+				if (b_ciph[j])
+					b_bits_xmy[j] *= -1;
+		}
+
+		gmr1_scramble_sbit(b_bits_ep, b_bits_xmy, 96);
+		gmr1_deinterleave_intra(b_bits_cp, b_bits_ep, 12);
+	};
+
+	for (i=0; i<384; i++)
+		bits_c[i] = bits_cp[(i&3)*96 + (i>>2)];
+
+	rv = osmo_conv_decode(&gmr1_conv_facch3, bits_c, bits_u);
+	if (conv_rv)
+		*conv_rv = rv;
+
+	rv = osmo_crc16gen_check_bits(&gmr1_crc16, bits_u, 76, bits_u+76);
+
+	l2[9] = 0; /* upper nibble won't be written */
+	osmo_ubit2pbit_ext(l2, 0, bits_u, 0, 76, 1);
+
+	return rv;
+}
+
+/*! }@ */