add (untested) 16kbit E1 sub-channel demux with TRAU frame sync

1 files changed, 166 insertions, 0 deletions

diff --git a/src/subchan_demux.c b/src/subchan_demux.c
new file mode 100644
index 000000000..34a5af010
--- /dev/null
+++ b/src/subchan_demux.c
@@ -0,0 +1,166 @@
+/* A E1 sub-channel demultiplexer with TRAU frame sync */
+
+/* (C) 2009 by Harald Welte <laforge@gnumonks.org>
+ * All Rights Reserved
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+
+#include <openbsc/subchan_demux.h>
+
+static inline void append_bit(struct subch *sch, u_int8_t bit)
+{
+	sch->out_bitbuf[sch->out_idx++] = bit;
+}
+
+#define SYNC_HDR_BITS	16
+static const u_int8_t nullbytes[SYNC_HDR_BITS];
+
+/* check if we have just completed the 16 bit zero sync header,
+ * in accordance with GSM TS 08.60 Chapter 4.8.1 */
+static int sync_hdr_complete(struct subch *sch)
+{
+	int rc;
+	int bits_at_end = 0;
+	int bits_at_front;
+ 
+	if (sch->out_idx < SYNC_HDR_BITS)
+		bits_at_end = SYNC_HDR_BITS - sch->out_idx;
+	bits_at_front = sch->out_idx;
+
+	if (bits_at_end) {
+		rc = memcmp(sch->out_bitbuf + sizeof(sch->out_bitbuf) - bits_at_end,
+			    nullbytes, bits_at_end);
+		if (rc)
+			return 0;
+	}
+	rc = memcmp(sch->out_bitbuf + sch->out_idx, nullbytes,
+		    bits_at_front);
+	if (rc)
+		return 0;
+	
+	return 1;
+}
+
+/* resynchronize to current location */
+static void resync_to_here(struct subch *sch)
+{
+#if 0
+	u_int8_t tmp[TRAU_FRAME_BITS];
+	int sync_hdr_start = sch->out_idx - SYNC_HDR_BITS;
+	int bytes_at_end;
+
+	/* first make copy of old bitbuf */
+	memcpy(tmp, sch->out_bitbuf, sizeof(tmp));
+
+	if (sync_hdr_start < 0)
+		sync_hdr_start += TRAU_FRAME_BITS;
+
+	bytes_at_end = TRAU_FRAME_BITS - sync_hdr_start;
+
+	/* copy part after sync_hdr_start */
+	memcpy(sch->out_bitbuf, tmp + sync_hdr_start, bytes_at_end);
+
+	/* copy part before sync_hdr_start */
+	memcpy(sch->out_bitbuf + bytes_at_end, tmp, 
+		SYNC_HDR_BITS - bytes_at_end);
+#else
+	memset(sch->out_bitbuf, 0, SYNC_HDR_BITS);
+#endif
+
+	/* set index in a way that we can continue receiving bits after
+	 * the end of the SYNC header */
+	sch->out_idx = SYNC_HDR_BITS;
+}
+
+/* input some arbitrary (modulo 4) number of bytes of a 64k E1 channel,
+ * split it into the 16k subchannels */
+int subch_demux_in(struct subch_demux *dmx, u_int8_t *data, int len)
+{
+	int i, c;
+
+	/* we avoid partially filled bytes in outbuf */
+	if (len % 4)
+		return -EINVAL;
+
+	for (i = 0; i < len; i++) {
+		u_int8_t inbyte = data[i];
+
+		for (c = 0; c < NR_SUBCH; c++) {
+			struct subch *sch = &dmx->subch[c];
+			u_int8_t bit;
+
+			/* ignore inactive subchannels */
+			if (!(dmx->chan_activ & (1 << c)))
+				continue;
+
+			/* two bits for each subchannel */
+			if ((inbyte >> (c * 2)) & 0x01)
+				bit = 1;
+			else
+				bit = 0;
+			append_bit(sch, bit);
+
+			if (sync_hdr_complete(sch))
+				resync_to_here(sch);
+
+			if ((inbyte >> (c * 2)) & 0x02)
+				bit = 1;
+			else
+				bit = 0;
+			append_bit(sch, bit);
+
+			if (sync_hdr_complete(sch))
+				resync_to_here(sch);
+
+			/* FIXME: verify the first bit in octet 2, 4, 6, ...
+			 * according to TS 08.60 4.8.1 */
+
+			/* once we have reached TRAU_FRAME_BITS, call
+			 * the TRAU frame handler callback function */
+			if (sch->out_idx >= TRAU_FRAME_BITS) {
+				dmx->out_cb(dmx, c, sch->out_bitbuf,
+					    sch->out_idx, dmx->data);
+				sch->out_idx = 0;
+			}
+		}
+	}
+	return i;
+}
+
+int subch_demux_activate(struct subch_demux *dmx, int subch)
+{
+	if (subch >= NR_SUBCH)
+		return -EINVAL;
+
+	dmx->chan_activ |= (1 << subch);
+	return 0;
+}
+
+int subch_demux_deactivate(struct subch_demux *dmx, int subch)
+{
+	if (subch >= NR_SUBCH)
+		return -EINVAL;
+
+	dmx->chan_activ &= ~(1 << subch);
+	return 0;
+}