l1/ccch: Add CCCH (PCH/AGCH) channel coding

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

2 files changed, 114 insertions, 1 deletions

diff --git a/src/l1/Makefile.am b/src/l1/Makefile.am
index fcc8568..4857242 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
+	bcch.c ccch.c
diff --git a/src/l1/ccch.c b/src/l1/ccch.c
new file mode 100644
index 0000000..4ece592
--- /dev/null
+++ b/src/l1/ccch.c
@@ -0,0 +1,113 @@
+/* GMR-1 CCCH channel coding */
+/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.2 & 6.3 */
+
+/* (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 ccch
+ *  @{
+ */
+
+/*! \file l1/ccch.c
+ *  \brief Osmocom GMR-1 CCCH (PCH/AGCH) 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_ccch;
+static int ccch_init_done = 0;
+
+static void
+gmr1_ccch_init(void)
+{
+	/* Init convolutional coder */
+	memcpy(&gmr1_conv_ccch, &gmr1_conv_12, sizeof(struct osmo_conv_code));
+	gmr1_conv_ccch.len = 208;
+
+	/* Init done */
+	ccch_init_done = 1;
+}
+
+#define GMR1_CCCH_CHECK_INIT if (!ccch_init_done) gmr1_ccch_init()
+
+
+/*! \brief Stateless GMR-1 CCCH channel coder
+ *  \param[out] bits_e Data bits of a burst
+ *  \param[in] l2 L2 packet data
+ *
+ * L2 data is 24 byte long, and bits_e is a 432 hard bit array to be
+ * mapped on a burst.
+ */
+void
+gmr1_ccch_encode(ubit_t *bits_e, uint8_t *l2)
+{
+	ubit_t bits_u[208];
+	ubit_t bits_c[428];
+	ubit_t bits_ep[432];
+	int i;
+
+	GMR1_CCCH_CHECK_INIT;
+
+	for (i=0; i<4; i++)
+		bits_ep[i] = bits_ep[431-i] = 0;
+
+	osmo_pbit2ubit_ext(bits_u, 0, l2, 0, 192, 1);
+	osmo_crc16gen_set_bits(&gmr1_crc16, bits_u, 192, bits_u+192);
+	osmo_conv_encode(&gmr1_conv_ccch, bits_u, bits_c);
+	gmr1_interleave_intra(&bits_ep[4], bits_c, 53);
+	gmr1_scramble_ubit(bits_e, bits_ep, 432);
+}
+
+/*! \brief Stateless GMR-1 CCCH channel decoder
+ *  \param[out] l2 L2 packet data
+ *  \param[in] bits_e Data bits of a burst
+ *
+ * L2 data is 24 byte long, and bits_e is a 432 hard bit array to be
+ * mapped on a burst.
+ */
+int
+gmr1_ccch_decode(uint8_t *l2, sbit_t *bits_e, int *conv_rv)
+{
+	sbit_t bits_ep[432];
+	sbit_t bits_c[428];
+	ubit_t bits_u[208];
+	int rv;
+
+	GMR1_CCCH_CHECK_INIT;
+
+	gmr1_scramble_sbit(bits_ep, bits_e, 432);
+	gmr1_deinterleave_intra(bits_c, &bits_ep[4], 53);
+
+	rv = osmo_conv_decode(&gmr1_conv_ccch, bits_c, bits_u);
+	if (conv_rv)
+		*conv_rv = rv;
+
+	rv = osmo_crc16gen_check_bits(&gmr1_crc16, bits_u, 192, bits_u+192);
+
+	osmo_ubit2pbit_ext(l2, 0, bits_u, 0, 192, 1);
+
+	return rv;
+}
+
+/*! }@ */