diff options
Diffstat (limited to 'src/codec')
| -rw-r--r-- | src/codec/Makefile.am | 2 | ||||
| -rw-r--r-- | src/codec/ecu_fr.c | 165 |
2 files changed, 166 insertions, 1 deletions
diff --git a/src/codec/Makefile.am b/src/codec/Makefile.am index b4df5da7..f77d910b 100644 --- a/src/codec/Makefile.am +++ b/src/codec/Makefile.am @@ -13,6 +13,6 @@ endif lib_LTLIBRARIES = libosmocodec.la -libosmocodec_la_SOURCES = gsm610.c gsm620.c gsm660.c gsm690.c +libosmocodec_la_SOURCES = gsm610.c gsm620.c gsm660.c gsm690.c ecu_fr.c libosmocodec_la_LDFLAGS = -version-info $(LIBVERSION) -no-undefined libosmocodec_la_LIBADD = $(top_builddir)/src/libosmocore.la diff --git a/src/codec/ecu_fr.c b/src/codec/ecu_fr.c new file mode 100644 index 00000000..d4ea741b --- /dev/null +++ b/src/codec/ecu_fr.c @@ -0,0 +1,165 @@ +/* + * (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 = false; + + if (reduce_xmaxcr(frame_bitvec, GSM610_RTP_XMAXC00)) + silent = true; + if (reduce_xmaxcr(frame_bitvec, GSM610_RTP_XMAXC10)) + silent = true; + if (reduce_xmaxcr(frame_bitvec, GSM610_RTP_XMAXC20)) + silent = true; + if (reduce_xmaxcr(frame_bitvec, GSM610_RTP_XMAXC30)) + silent = true; + + 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. + */ +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. + */ +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; +} |