l1/bcch: Add complete BCCH stateless coder/decoder

The BCCH doesn't have inter-burst dependency, hence we just
have a stateless coding/decoding routine.

See GMR 05.003 Section 6.1

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

1 files changed, 109 insertions, 0 deletions

diff --git a/src/l1/bcch.c b/src/l1/bcch.c
new file mode 100644
index 0000000..3fed54a
--- /dev/null
+++ b/src/l1/bcch.c
@@ -0,0 +1,109 @@
+/* GMR-1 BCCH channel coding */
+/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.1 */
+
+/* (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 bcch
+ *  @{
+ */
+
+/*! \file bcch.c
+ *  \file Osmocom GMR-1 BCCH channel coding header
+ */
+
+#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_bcch;
+static int bcch_init_done = 0;
+
+static void
+gmr1_bcch_init(void)
+{
+	/* Init convolutional coder */
+	memcpy(&gmr1_conv_bcch, &gmr1_conv_12, sizeof(struct osmo_conv_code));
+	gmr1_conv_bcch.len = 208;
+
+	/* Init done */
+	bcch_init_done = 1;
+}
+
+#define GMR1_BCCH_CHECK_INIT if (!bcch_init_done) gmr1_bcch_init()
+
+
+/*! \brief Stateless GMR-1 BCCH 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 424 hard bit array to be
+ * mapped on a burst.
+ */
+void
+gmr1_bcch_encode(ubit_t *bits_e, uint8_t *l2)
+{
+	ubit_t bits_u[208];
+	ubit_t bits_c[424];
+	ubit_t bits_ep[424];
+
+	GMR1_BCCH_CHECK_INIT;
+
+	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_bcch, bits_u, bits_c);
+	gmr1_interleave_intra(bits_ep, bits_c, 53);
+	gmr1_scramble_ubit(bits_e, bits_ep, 424); 
+}
+
+/*! \brief Stateless GMR-1 BCCH 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 424 hard bit array to be
+ * mapped on a burst.
+ */
+int
+gmr1_bcch_decode(uint8_t *l2, sbit_t *bits_e, int *conv_rv)
+{
+	sbit_t bits_ep[424];
+	sbit_t bits_c[424];
+	ubit_t bits_u[208];
+	int rv;
+
+	GMR1_BCCH_CHECK_INIT;
+
+	gmr1_scramble_sbit(bits_ep, bits_e, 424); 
+	gmr1_deinterleave_intra(bits_c, bits_ep, 53);
+
+	rv = osmo_conv_decode(&gmr1_conv_bcch, 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;
+}
+
+/*! }@ */