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Diffstat (limited to 'src/libtrau/subchan_demux.c')
-rw-r--r-- | src/libtrau/subchan_demux.c | 321 |
1 files changed, 321 insertions, 0 deletions
diff --git a/src/libtrau/subchan_demux.c b/src/libtrau/subchan_demux.c new file mode 100644 index 000000000..6bcf279fe --- /dev/null +++ b/src/libtrau/subchan_demux.c @@ -0,0 +1,321 @@ +/* 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 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/>. + * + */ + +#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> +#include <osmocore/talloc.h> +#include <openbsc/gsm_data.h> + +void *tall_tqe_ctx; + +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); + talloc_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); + talloc_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]; + int list_len = llist_len(&sch->tx_queue); + struct subch_txq_entry *tqe = talloc_zero_size(tall_tqe_ctx, + sizeof(*tqe) + len); + if (!tqe) + return -ENOMEM; + + 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; +} |