| /* 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; |
| } |
| |
| /* 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; |
| } |