323 lines
7.3 KiB
C
323 lines
7.3 KiB
C
/* A E1 sub-channel (de)multiplexer with TRAU frame sync */
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/* (C) 2009 by Harald Welte <laforge@gnumonks.org>
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* All Rights Reserved
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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*/
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#include <unistd.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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#include <errno.h>
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#include <openbsc/subchan_demux.h>
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#include <openbsc/trau_frame.h>
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#include <openbsc/debug.h>
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#include <openbsc/talloc.h>
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#include <openbsc/gsm_data.h>
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void *tall_tqe_ctx;
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static inline void append_bit(struct demux_subch *sch, u_int8_t bit)
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{
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sch->out_bitbuf[sch->out_idx++] = bit;
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}
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#define SYNC_HDR_BITS 16
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static const u_int8_t nullbytes[SYNC_HDR_BITS];
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/* check if we have just completed the 16 bit zero sync header,
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* in accordance with GSM TS 08.60 Chapter 4.8.1 */
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static int sync_hdr_complete(struct demux_subch *sch, u_int8_t bit)
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{
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if (bit == 0)
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sch->consecutive_zeros++;
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else
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sch->consecutive_zeros = 0;
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if (sch->consecutive_zeros >= SYNC_HDR_BITS) {
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sch->consecutive_zeros = 0;
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return 1;
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}
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return 0;
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}
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/* resynchronize to current location */
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static void resync_to_here(struct demux_subch *sch)
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{
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memset(sch->out_bitbuf, 0, SYNC_HDR_BITS);
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/* set index in a way that we can continue receiving bits after
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* the end of the SYNC header */
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sch->out_idx = SYNC_HDR_BITS;
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sch->in_sync = 1;
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}
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int subch_demux_init(struct subch_demux *dmx)
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{
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int i;
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dmx->chan_activ = 0;
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for (i = 0; i < NR_SUBCH; i++) {
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struct demux_subch *sch = &dmx->subch[i];
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sch->out_idx = 0;
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memset(sch->out_bitbuf, 0xff, sizeof(sch->out_bitbuf));
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}
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return 0;
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}
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/* input some arbitrary (modulo 4) number of bytes of a 64k E1 channel,
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* split it into the 16k subchannels */
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int subch_demux_in(struct subch_demux *dmx, u_int8_t *data, int len)
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{
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int i, c;
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/* we avoid partially filled bytes in outbuf */
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if (len % 4)
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return -EINVAL;
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for (i = 0; i < len; i++) {
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u_int8_t inbyte = data[i];
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for (c = 0; c < NR_SUBCH; c++) {
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struct demux_subch *sch = &dmx->subch[c];
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u_int8_t inbits;
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u_int8_t bit;
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/* ignore inactive subchannels */
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if (!(dmx->chan_activ & (1 << c)))
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continue;
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inbits = inbyte >> (c << 1);
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/* two bits for each subchannel */
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if (inbits & 0x01)
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bit = 1;
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else
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bit = 0;
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append_bit(sch, bit);
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if (sync_hdr_complete(sch, bit))
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resync_to_here(sch);
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if (inbits & 0x02)
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bit = 1;
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else
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bit = 0;
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append_bit(sch, bit);
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if (sync_hdr_complete(sch, bit))
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resync_to_here(sch);
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/* FIXME: verify the first bit in octet 2, 4, 6, ...
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* according to TS 08.60 4.8.1 */
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/* once we have reached TRAU_FRAME_BITS, call
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* the TRAU frame handler callback function */
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if (sch->out_idx >= TRAU_FRAME_BITS) {
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if (sch->in_sync) {
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dmx->out_cb(dmx, c, sch->out_bitbuf,
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sch->out_idx, dmx->data);
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sch->in_sync = 0;
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}
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sch->out_idx = 0;
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}
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}
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}
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return i;
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}
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int subch_demux_activate(struct subch_demux *dmx, int subch)
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{
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if (subch >= NR_SUBCH)
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return -EINVAL;
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dmx->chan_activ |= (1 << subch);
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return 0;
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}
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int subch_demux_deactivate(struct subch_demux *dmx, int subch)
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{
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if (subch >= NR_SUBCH)
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return -EINVAL;
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dmx->chan_activ &= ~(1 << subch);
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return 0;
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}
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/* MULTIPLEXER */
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static int alloc_add_idle_frame(struct subch_mux *mx, int sch_nr)
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{
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/* allocate and initialize with idle pattern */
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return subchan_mux_enqueue(mx, sch_nr, trau_idle_frame(),
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TRAU_FRAME_BITS);
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}
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/* return the requested number of bits from the specified subchannel */
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static int get_subch_bits(struct subch_mux *mx, int subch,
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u_int8_t *bits, int num_requested)
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{
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struct mux_subch *sch = &mx->subch[subch];
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int num_bits = 0;
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while (num_bits < num_requested) {
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struct subch_txq_entry *txe;
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int num_bits_left;
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int num_bits_thistime;
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/* make sure we have a valid entry at top of tx queue.
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* if not, add an idle frame */
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if (llist_empty(&sch->tx_queue))
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alloc_add_idle_frame(mx, subch);
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if (llist_empty(&sch->tx_queue))
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return -EIO;
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txe = llist_entry(sch->tx_queue.next, struct subch_txq_entry, list);
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num_bits_left = txe->bit_len - txe->next_bit;
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if (num_bits_left < num_requested)
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num_bits_thistime = num_bits_left;
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else
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num_bits_thistime = num_requested;
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/* pull the bits from the txe */
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memcpy(bits + num_bits, txe->bits + txe->next_bit, num_bits_thistime);
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txe->next_bit += num_bits_thistime;
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/* free the tx_queue entry if it is fully consumed */
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if (txe->next_bit >= txe->bit_len) {
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llist_del(&txe->list);
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talloc_free(txe);
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}
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/* increment global number of bits dequeued */
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num_bits += num_bits_thistime;
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}
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return num_requested;
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}
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/* compact an array of 8 single-bit bytes into one byte of 8 bits */
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static u_int8_t compact_bits(const u_int8_t *bits)
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{
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u_int8_t ret = 0;
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int i;
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for (i = 0; i < 8; i++)
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ret |= (bits[i] ? 1 : 0) << i;
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return ret;
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}
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/* obtain a single output byte from the subchannel muxer */
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static int mux_output_byte(struct subch_mux *mx, u_int8_t *byte)
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{
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u_int8_t bits[8];
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int rc;
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/* combine two bits of every subchan */
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rc = get_subch_bits(mx, 0, &bits[0], 2);
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rc = get_subch_bits(mx, 1, &bits[2], 2);
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rc = get_subch_bits(mx, 2, &bits[4], 2);
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rc = get_subch_bits(mx, 3, &bits[6], 2);
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*byte = compact_bits(bits);
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return rc;
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}
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/* Request the output of some muxed bytes from the subchan muxer */
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int subchan_mux_out(struct subch_mux *mx, u_int8_t *data, int len)
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{
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int i;
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for (i = 0; i < len; i++) {
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int rc;
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rc = mux_output_byte(mx, &data[i]);
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if (rc < 0)
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break;
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}
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return i;
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}
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static int llist_len(struct llist_head *head)
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{
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struct llist_head *entry;
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int i = 0;
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llist_for_each(entry, head)
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i++;
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return i;
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}
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/* evict the 'num_evict' number of oldest entries in the queue */
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static void tx_queue_evict(struct mux_subch *sch, int num_evict)
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{
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struct subch_txq_entry *tqe;
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int i;
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for (i = 0; i < num_evict; i++) {
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if (llist_empty(&sch->tx_queue))
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return;
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tqe = llist_entry(sch->tx_queue.next, struct subch_txq_entry, list);
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llist_del(&tqe->list);
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talloc_free(tqe);
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}
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}
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/* enqueue some data into the tx_queue of a given subchannel */
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int subchan_mux_enqueue(struct subch_mux *mx, int s_nr, const u_int8_t *data,
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int len)
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{
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struct mux_subch *sch = &mx->subch[s_nr];
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int list_len = llist_len(&sch->tx_queue);
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struct subch_txq_entry *tqe = talloc_zero_size(tall_tqe_ctx,
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sizeof(*tqe) + len);
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if (!tqe)
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return -ENOMEM;
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tqe->bit_len = len;
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memcpy(tqe->bits, data, len);
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if (list_len > 2)
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tx_queue_evict(sch, list_len-2);
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llist_add_tail(&tqe->list, &sch->tx_queue);
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return 0;
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}
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/* initialize one subchannel muxer instance */
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int subchan_mux_init(struct subch_mux *mx)
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{
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int i;
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memset(mx, 0, sizeof(*mx));
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for (i = 0; i < NR_SUBCH; i++) {
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struct mux_subch *sch = &mx->subch[i];
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INIT_LLIST_HEAD(&sch->tx_queue);
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}
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return 0;
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}
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