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/*
* (C) 2017 by sysmocom - s.f.m.c. GmbH
* (C) 2017 by Philipp Maier <pmaier@sysmocom.de>
*
* 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 <stdbool.h>
#include <string.h>
#include <stdint.h>
#include <errno.h>
#include <osmocom/core/bitvec.h>
#include <osmocom/codec/gsm610_bits.h>
#include <osmocom/codec/codec.h>
#include <osmocom/codec/ecu.h>
/* See also GSM 06.11, chapter 6 Example solution */
#define GSM610_XMAXC_REDUCE 4
#define GSM610_XMAXC_LEN 6
/**
* Reduce the XMAXC field. When the XMAXC field reaches
* zero the function will return true.
*/
static bool reduce_xmaxcr(struct bitvec *frame_bitvec,
const unsigned int index)
{
unsigned int field_index;
uint64_t field;
field_index = index;
field = bitvec_read_field(frame_bitvec, &field_index, GSM610_XMAXC_LEN);
if (field > GSM610_XMAXC_REDUCE)
field -= GSM610_XMAXC_REDUCE;
else
field = 0;
field_index = index;
bitvec_write_field(frame_bitvec, &field_index, field, GSM610_XMAXC_LEN);
return field == 0;
}
/**
* Reduce all XMAXC fields in the frame. When all XMAXC fields
* reach zero, then the function will return true.
*/
static bool reduce_xmaxcr_all(struct bitvec *frame_bitvec)
{
bool silent = true;
silent &= reduce_xmaxcr(frame_bitvec, GSM610_RTP_XMAXC00);
silent &= reduce_xmaxcr(frame_bitvec, GSM610_RTP_XMAXC10);
silent &= reduce_xmaxcr(frame_bitvec, GSM610_RTP_XMAXC20);
silent &= reduce_xmaxcr(frame_bitvec, GSM610_RTP_XMAXC30);
return silent;
}
/* Use certain modifications to conceal the errors in a full rate frame */
static int conceal_frame(uint8_t *frame)
{
struct bitvec *frame_bitvec;
unsigned int len;
bool silent;
int rc = 0;
/* In case we already deal with a silent frame,
* there is nothing to, we just abort immediately */
if (osmo_fr_check_sid(frame, GSM_FR_BYTES))
return 0;
/* Attempt to allocate memory for bitvec */
frame_bitvec = bitvec_alloc(GSM_FR_BYTES, NULL);
if (!frame_bitvec)
return -ENOMEM;
/* Convert a frame to bitvec */
len = bitvec_unpack(frame_bitvec, frame);
if (len != GSM_FR_BYTES) {
rc = -EIO;
goto leave;
}
/* Fudge frame parameters */
silent = reduce_xmaxcr_all(frame_bitvec);
/* If we reached silence level, mute the frame
* completely, this also means that we can
* save the bitvec_pack operation */
if (silent) {
memset(frame, 0x00, GSM_FR_BYTES);
frame[0] = 0xd0;
goto leave;
}
/* Convert back to packed byte form */
len = bitvec_pack(frame_bitvec, frame);
if (len != GSM_FR_BYTES) {
rc = -EIO;
goto leave;
}
leave:
bitvec_free(frame_bitvec);
return rc;
}
/*!
* To be called when a good frame is received.
* This function will then create a backup of the frame
* and reset the internal state.
* \param[in] state The state object for the ECU
* \param[out] frame The valid frame (GSM_FR_BYTES bytes in RTP payload format)
*/
void osmo_ecu_fr_reset(struct osmo_ecu_fr_state *state, uint8_t *frame)
{
state->subsequent_lost_frame = false;
memcpy(state->frame_backup, frame, GSM_FR_BYTES);
}
/*!
* To be called when a bad frame is received.
* This function will then generate a replacement frame
* that can be used to conceal the dropout.
* \param[in] state The state object for the ECU
* \param[out] frame The buffer to fill with GSM_FR_BYTES of replacement frame
* \returns 0 if the frame was sucessfully filled
*/
int osmo_ecu_fr_conceal(struct osmo_ecu_fr_state *state, uint8_t *frame)
{
int rc;
/* For subsequent frames we run the error concealment
* functions on the backed up frame before we restore
* the backup */
if (state->subsequent_lost_frame) {
rc = conceal_frame(state->frame_backup);
if (rc)
return rc;
}
/* Restore the backed up frame and set flag in case
* we receive even more bad frames */
memcpy(frame, state->frame_backup, GSM_FR_BYTES);
state->subsequent_lost_frame = true;
return 0;
}
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