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-rw-r--r--openbsc/src/subchan_demux.c319
1 files changed, 319 insertions, 0 deletions
diff --git a/openbsc/src/subchan_demux.c b/openbsc/src/subchan_demux.c
new file mode 100644
index 000000000..c662bcd0e
--- /dev/null
+++ b/openbsc/src/subchan_demux.c
@@ -0,0 +1,319 @@
+/* A E1 sub-channel (de)multiplexer 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>
+#include <openbsc/trau_frame.h>
+#include <openbsc/debug.h>
+
+static inline void append_bit(struct demux_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 demux_subch *sch, u_int8_t bit)
+{
+ if (bit == 0)
+ sch->consecutive_zeros++;
+ else
+ sch->consecutive_zeros = 0;
+
+ if (sch->consecutive_zeros >= SYNC_HDR_BITS) {
+ sch->consecutive_zeros = 0;
+ return 1;
+ }
+
+ return 0;
+}
+
+/* resynchronize to current location */
+static void resync_to_here(struct demux_subch *sch)
+{
+ memset(sch->out_bitbuf, 0, SYNC_HDR_BITS);
+
+ /* set index in a way that we can continue receiving bits after
+ * the end of the SYNC header */
+ sch->out_idx = SYNC_HDR_BITS;
+ sch->in_sync = 1;
+}
+
+int subch_demux_init(struct subch_demux *dmx)
+{
+ int i;
+
+ dmx->chan_activ = 0;
+ for (i = 0; i < NR_SUBCH; i++) {
+ struct demux_subch *sch = &dmx->subch[i];
+ sch->out_idx = 0;
+ memset(sch->out_bitbuf, 0xff, sizeof(sch->out_bitbuf));
+ }
+ return 0;
+}
+
+/* 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 demux_subch *sch = &dmx->subch[c];
+ u_int8_t inbits;
+ u_int8_t bit;
+
+ /* ignore inactive subchannels */
+ if (!(dmx->chan_activ & (1 << c)))
+ continue;
+
+ inbits = inbyte >> (c << 1);
+
+ /* two bits for each subchannel */
+ if (inbits & 0x01)
+ bit = 1;
+ else
+ bit = 0;
+ append_bit(sch, bit);
+
+ if (sync_hdr_complete(sch, bit))
+ resync_to_here(sch);
+
+ if (inbits & 0x02)
+ bit = 1;
+ else
+ bit = 0;
+ append_bit(sch, bit);
+
+ if (sync_hdr_complete(sch, bit))
+ 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) {
+ if (sch->in_sync) {
+ dmx->out_cb(dmx, c, sch->out_bitbuf,
+ sch->out_idx, dmx->data);
+ sch->in_sync = 0;
+ }
+ 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;
+}
+
+/* MULTIPLEXER */
+
+static int alloc_add_idle_frame(struct subch_mux *mx, int sch_nr)
+{
+ /* allocate and initialize with idle pattern */
+ return subchan_mux_enqueue(mx, sch_nr, trau_idle_frame(),
+ TRAU_FRAME_BITS);
+}
+
+/* return the requested number of bits from the specified subchannel */
+static int get_subch_bits(struct subch_mux *mx, int subch,
+ u_int8_t *bits, int num_requested)
+{
+ struct mux_subch *sch = &mx->subch[subch];
+ int num_bits = 0;
+
+ while (num_bits < num_requested) {
+ struct subch_txq_entry *txe;
+ int num_bits_left;
+ int num_bits_thistime;
+
+ /* make sure we have a valid entry at top of tx queue.
+ * if not, add an idle frame */
+ if (llist_empty(&sch->tx_queue))
+ alloc_add_idle_frame(mx, subch);
+
+ if (llist_empty(&sch->tx_queue))
+ return -EIO;
+
+ txe = llist_entry(sch->tx_queue.next, struct subch_txq_entry, list);
+ num_bits_left = txe->bit_len - txe->next_bit;
+
+ if (num_bits_left < num_requested)
+ num_bits_thistime = num_bits_left;
+ else
+ num_bits_thistime = num_requested;
+
+ /* pull the bits from the txe */
+ memcpy(bits + num_bits, txe->bits + txe->next_bit, num_bits_thistime);
+ txe->next_bit += num_bits_thistime;
+
+ /* free the tx_queue entry if it is fully consumed */
+ if (txe->next_bit >= txe->bit_len) {
+ llist_del(&txe->list);
+ free(txe);
+ }
+
+ /* increment global number of bits dequeued */
+ num_bits += num_bits_thistime;
+ }
+
+ return num_requested;
+}
+
+/* compact an array of 8 single-bit bytes into one byte of 8 bits */
+static u_int8_t compact_bits(const u_int8_t *bits)
+{
+ u_int8_t ret = 0;
+ int i;
+
+ for (i = 0; i < 8; i++)
+ ret |= (bits[i] ? 1 : 0) << i;
+
+ return ret;
+}
+
+/* obtain a single output byte from the subchannel muxer */
+static int mux_output_byte(struct subch_mux *mx, u_int8_t *byte)
+{
+ u_int8_t bits[8];
+ int rc;
+
+ /* combine two bits of every subchan */
+ rc = get_subch_bits(mx, 0, &bits[0], 2);
+ rc = get_subch_bits(mx, 1, &bits[2], 2);
+ rc = get_subch_bits(mx, 2, &bits[4], 2);
+ rc = get_subch_bits(mx, 3, &bits[6], 2);
+
+ *byte = compact_bits(bits);
+
+ return rc;
+}
+
+/* Request the output of some muxed bytes from the subchan muxer */
+int subchan_mux_out(struct subch_mux *mx, u_int8_t *data, int len)
+{
+ int i;
+
+ for (i = 0; i < len; i++) {
+ int rc;
+ rc = mux_output_byte(mx, &data[i]);
+ if (rc < 0)
+ break;
+ }
+ return i;
+}
+
+static int llist_len(struct llist_head *head)
+{
+ struct llist_head *entry;
+ int i = 0;
+
+ llist_for_each(entry, head)
+ i++;
+
+ return i;
+}
+
+/* evict the 'num_evict' number of oldest entries in the queue */
+static void tx_queue_evict(struct mux_subch *sch, int num_evict)
+{
+ struct subch_txq_entry *tqe;
+ int i;
+
+ for (i = 0; i < num_evict; i++) {
+ if (llist_empty(&sch->tx_queue))
+ return;
+
+ tqe = llist_entry(sch->tx_queue.next, struct subch_txq_entry, list);
+ llist_del(&tqe->list);
+ free(tqe);
+ }
+}
+
+/* enqueue some data into the tx_queue of a given subchannel */
+int subchan_mux_enqueue(struct subch_mux *mx, int s_nr, const u_int8_t *data,
+ int len)
+{
+ struct mux_subch *sch = &mx->subch[s_nr];
+ struct subch_txq_entry *tqe = malloc(sizeof(*tqe) + len);
+ int list_len = llist_len(&sch->tx_queue);
+
+ if (!tqe)
+ return -ENOMEM;
+
+ memset(tqe, 0, sizeof(*tqe));
+ tqe->bit_len = len;
+ memcpy(tqe->bits, data, len);
+
+ if (list_len > 2)
+ tx_queue_evict(sch, list_len-2);
+
+ llist_add_tail(&tqe->list, &sch->tx_queue);
+
+ return 0;
+}
+
+/* initialize one subchannel muxer instance */
+int subchan_mux_init(struct subch_mux *mx)
+{
+ int i;
+
+ memset(mx, 0, sizeof(*mx));
+ for (i = 0; i < NR_SUBCH; i++) {
+ struct mux_subch *sch = &mx->subch[i];
+ INIT_LLIST_HEAD(&sch->tx_queue);
+ }
+
+ return 0;
+}