180 lines
4.3 KiB
C
180 lines
4.3 KiB
C
/* A E1 sub-channel demultiplexer 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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static inline void append_bit(struct 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 subch *sch)
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{
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int rc;
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int bits_at_end = 0;
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int bits_at_front;
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if (sch->out_idx < SYNC_HDR_BITS)
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bits_at_end = SYNC_HDR_BITS - sch->out_idx;
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bits_at_front = sch->out_idx;
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if (bits_at_end) {
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rc = memcmp(sch->out_bitbuf + sizeof(sch->out_bitbuf) - bits_at_end,
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nullbytes, bits_at_end);
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if (rc)
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return 0;
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}
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rc = memcmp(sch->out_bitbuf + sch->out_idx, nullbytes,
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bits_at_front);
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if (rc)
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return 0;
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return 1;
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}
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/* resynchronize to current location */
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static void resync_to_here(struct subch *sch)
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{
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#if 0
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u_int8_t tmp[TRAU_FRAME_BITS];
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int sync_hdr_start = sch->out_idx - SYNC_HDR_BITS;
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int bytes_at_end;
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/* first make copy of old bitbuf */
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memcpy(tmp, sch->out_bitbuf, sizeof(tmp));
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if (sync_hdr_start < 0)
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sync_hdr_start += TRAU_FRAME_BITS;
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bytes_at_end = TRAU_FRAME_BITS - sync_hdr_start;
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/* copy part after sync_hdr_start */
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memcpy(sch->out_bitbuf, tmp + sync_hdr_start, bytes_at_end);
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/* copy part before sync_hdr_start */
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memcpy(sch->out_bitbuf + bytes_at_end, tmp,
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SYNC_HDR_BITS - bytes_at_end);
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#else
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memset(sch->out_bitbuf, 0, SYNC_HDR_BITS);
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#endif
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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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}
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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 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 subch *sch = &dmx->subch[c];
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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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/* two bits for each subchannel */
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if ((inbyte >> (c * 2)) & 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))
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resync_to_here(sch);
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if ((inbyte >> (c * 2)) & 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))
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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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dmx->out_cb(dmx, c, sch->out_bitbuf,
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sch->out_idx, dmx->data);
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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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