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/* 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;
}
int subch_demux_init(struct subch_demux *dmx)
{
int i;
dmx->chan_activ = 0;
for (i = 0; i < NR_SUBCH; i++) {
struct 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 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;
}
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