diff options
Diffstat (limited to 'src/codec/ecu_fr.c')
-rw-r--r-- | src/codec/ecu_fr.c | 387 |
1 files changed, 257 insertions, 130 deletions
diff --git a/src/codec/ecu_fr.c b/src/codec/ecu_fr.c index 4545172a..45ba0cc8 100644 --- a/src/codec/ecu_fr.c +++ b/src/codec/ecu_fr.c @@ -1,9 +1,15 @@ /* * (C) 2017 by sysmocom - s.f.m.c. GmbH * (C) 2017 by Philipp Maier <pmaier@sysmocom.de> - * * All Rights Reserved * + * Significantly reworked in 2023 by Mother + * Mychaela N. Falconia <falcon@freecalypso.org> - however, + * Mother Mychaela's contributions are NOT subject to copyright. + * No rights reserved, all rights relinquished. + * Portions of this code are based on Themyscira libgsmfrp, + * a public domain library by the same author. + * * 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 @@ -14,10 +20,46 @@ * 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. * + * The present ECU implementation for GSM-FR is closely based on the + * TS 46.011 spec from 3GPP; more specifically, it is based on the + * Example solution presented in Chapter 6 of that spec, adapted for + * libosmocodec ECU architecture, and comes as close to fulfilling + * the spec's officially stated requirements (Chapter 5) as is + * possible within this Osmocom-imposed architecture. Please note + * the following areas where the present implementation fails to + * fulfill the original intent of GSM spec authors: + * + * - The "lost SID" criterion, defined in GSM 06.31, is based on the + * TAF bit from the Radio Subsystem. However, libosmocodec ECU API + * does not include this flag, thus spec requirements related to + * lost SID conditions cannot be implemented in a strictly compliant + * manner. The present implementation improvises its own "lost SID" + * detector (not strictly spec-compliant) by counting frame_out() + * calls in between good traffic frame inputs via frame_in(). + * + * - In the architecture envisioned and assumed in the GSM specs, + * the ECU function of GSM 06.11 was never intended to be a fully + * modular component with its own bona fide I/O interfaces - this + * approach appears to be an Osmocom invention - instead this ECU + * function was intended to be subsumed in the Rx DTX handler + * component of GSM 06.31, also incorporating the comfort noise + * generator of GSM 06.12 - and unlike the narrower-scope ECU, + * this slightly-larger-scope Rx DTX handler is a modular component + * with well-defined I/O interfaces. In the case of BFI conditions + * following a SID, GSM 06.11 spec was written with the assumption + * that the ECU controls the comfort noise generator via internal + * signals, as opposed to emitting "corrected" SID frames on a + * modular interface going to a CN generator located somewhere else. + * Thus the "correct" behavior for a fully modularized ECU is unclear, + * and an argument can be made that the very existence of such a + * fully modularized ECU is incorrect in itself. The present + * implementation re-emits a "rejuvenated" form of the last saved + * SID frame during BFI conditions following a SID within the + * permitted window of 48 frames, then starts emitting muted SIDs + * with Xmaxc decreasing by 4 on each frame, and finally switches + * to emitting non-SID silence frames (Table 1 of TS 46.011) + * once Xmaxc reaches 0. */ #include <stdbool.h> @@ -25,144 +67,216 @@ #include <stdint.h> #include <errno.h> -#include <osmocom/core/bitvec.h> +#include <osmocom/core/prbs.h> -#include <osmocom/codec/gsm610_bits.h> #include <osmocom/codec/codec.h> #include <osmocom/codec/ecu.h> +#include <osmocom/core/linuxlist.h> + +/* See TS 46.011, Chapter 6 Example solution */ +#define GSM611_XMAXC_REDUCE 4 + +/* The first 5 bytes of RTP encoding neatly contain the magic nibble + * and LARc parameters, which also happens to be the part of SID frames + * that needs to be passed through as-is. */ +#define SID_PREFIX_LEN 5 + +enum ecu_principal_state { + STATE_NO_DATA, + STATE_SPEECH, + STATE_SP_MUTING, + STATE_SID, + STATE_SID_MUTING, +}; -/* See also GSM 06.11, chapter 6 Example solution */ -#define GSM610_XMAXC_REDUCE 4 -#define GSM610_XMAXC_LEN 6 +struct fr_ecu_state { + struct osmo_ecu_state ecu_state; + enum ecu_principal_state pr_state; + uint8_t speech_frame[GSM_FR_BYTES]; + uint8_t sid_prefix[SID_PREFIX_LEN]; + uint8_t sid_xmaxc; + uint8_t sid_reemit_count; + struct osmo_prbs_state prng; + bool last_input_was_sid; +}; -/** - * Reduce the XMAXC field. When the XMAXC field reaches - * zero the function will return true. +/* This function is the frame input to the ECU - all inputs to this + * function have been received by the Radio Subsystem as good traffic + * frames in the GSM 06.31 definition. */ -static bool reduce_xmaxcr(struct bitvec *frame_bitvec, - const unsigned int index) +static void fr_ecu_input(struct fr_ecu_state *fr, const uint8_t *frame) { - 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; + enum osmo_gsm631_sid_class sidc; + + sidc = osmo_fr_sid_classify(frame); + switch (sidc) { + case OSMO_GSM631_SID_CLASS_SPEECH: + memcpy(fr->speech_frame, frame, GSM_FR_BYTES); + fr->pr_state = STATE_SPEECH; + fr->last_input_was_sid = false; + return; + case OSMO_GSM631_SID_CLASS_INVALID: + /* GSM 06.31 section 6.1.2 says: "an invalid SID frame + * shall be substituted by the last valid SID frame + * and the procedure for valid SID frames be applied." + * However, libosmocodec ECU architecture prevents us + * from doing what the spec says: the frame_in() method + * gets a const frame that can't be modified, and + * frame_out() will never get called when BFI=0, even + * when the "good traffic frame" (in the BFI=0 sense) + * is an invalid SID by the bit-counting rule. + * Thus there is no place where we can re-emit a cached + * copy of the last valid SID upon receiving an invalid SID. + * + * In the standard GSM architecture this problem never + * arises because the ECU is not a separate component + * but is coupled with the CN generator, thus the output + * from the Rx DTX handler block will be a CN frame, + * for both valid-SID and invalid-SID inputs to the block. + * But what can we do within the constraints of libosmocodec + * ECU framework? We treat the invalid SID almost like a + * BFI, doing almost nothing in the frame_in() method, + * but we reset sid_reemit_count because by the rules of + * GSM 06.31 an invalid SID is still an accepted SID frame + * for the purpose of "lost SID" logic. */ + fr->sid_reemit_count = 0; + fr->last_input_was_sid = true; + return; + case OSMO_GSM631_SID_CLASS_VALID: + /* save LARc part */ + memcpy(fr->sid_prefix, frame, SID_PREFIX_LEN); + /* save Xmaxc from the last subframe */ + fr->sid_xmaxc = ((frame[27] & 0x1F) << 1) | (frame[28] >> 7); + fr->pr_state = STATE_SID; + fr->sid_reemit_count = 0; + fr->last_input_was_sid = true; + return; + default: + /* There are only 3 possible SID classifications per GSM 06.31 + * section 6.1.1, thus any other return value is a grave error + * in the code. */ + OSMO_ASSERT(0); + } } -/** - * Reduce all XMAXC fields in the frame. When all XMAXC fields - * reach zero, then the function will return true. +/* Reduce all 4 Xmaxc fields in the frame. When all 4 Xmaxc fields + * reach 0, the function will return true for "mute". */ -static bool reduce_xmaxcr_all(struct bitvec *frame_bitvec) +static bool reduce_xmaxc(uint8_t *frame) { - 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; + bool mute_flag = true; + uint8_t sub, xmaxc; + + for (sub = 0; sub < 4; sub++) { + xmaxc = ((frame[sub*7+6] & 0x1F) << 1) | (frame[sub*7+7] >> 7); + if (xmaxc > GSM611_XMAXC_REDUCE) { + xmaxc -= GSM611_XMAXC_REDUCE; + mute_flag = false; + } else + xmaxc = 0; + frame[sub*7+6] &= 0xE0; + frame[sub*7+6] |= xmaxc >> 1; + frame[sub*7+7] &= 0x7F; + frame[sub*7+7] |= (xmaxc & 1) << 7; + } + return mute_flag; } -/* Use certain modifications to conceal the errors in a full rate frame */ -static int conceal_frame(uint8_t *frame) +/* TS 46.011 chapter 6, paragraph 4, last sentence: "The grid position + * parameters are chosen randomly between 0 and 3 during this time." + * (The "during this time" qualifier refers to the speech muting state.) + * This sentence in the spec must have been overlooked by previous ECU + * implementors, as this aspect of the muting logic was missing. + */ +static void random_grid_pos(struct fr_ecu_state *fr, 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; + uint8_t sub; - /* 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; + for (sub = 0; sub < 4; sub++) { + frame[sub*7+6] &= 0x9F; + frame[sub*7+6] |= osmo_prbs_get_ubit(&fr->prng) << 6; + frame[sub*7+6] |= osmo_prbs_get_ubit(&fr->prng) << 5; } +} - /* Convert back to packed byte form */ - len = bitvec_pack(frame_bitvec, frame); - if (len != GSM_FR_BYTES) { - rc = -EIO; - goto leave; +/* Like reduce_xmaxc() above, but for comfort noise rather than speech. */ +static bool reduce_xmaxc_sid(struct fr_ecu_state *fr) +{ + if (fr->sid_xmaxc > GSM611_XMAXC_REDUCE) { + fr->sid_xmaxc -= GSM611_XMAXC_REDUCE; + return false; } - -leave: - bitvec_free(frame_bitvec); - return rc; + fr->sid_xmaxc = 0; + return true; } -/*! - * 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) +/* This function implements the part which is peculiar to the present + * "standalone" packaging of GSM-FR ECU, without a directly coupled + * comfort noise generator - it re-emits synthetic SID frames during + * DTX pauses, initially unchanged from the saved SID and later muted. */ -void osmo_ecu_fr_reset(struct osmo_ecu_fr_state *state, const uint8_t *frame) +static void reemit_sid(struct fr_ecu_state *fr, uint8_t *frame) { - state->subsequent_lost_frame = false; - memcpy(state->frame_backup, frame, GSM_FR_BYTES); + uint8_t *p, sub; + + memcpy(frame, fr->sid_prefix, SID_PREFIX_LEN); + p = frame + SID_PREFIX_LEN; + for (sub = 0; sub < 4; sub++) { + *p++ = 0; + *p++ = fr->sid_xmaxc >> 1; + *p++ = (fr->sid_xmaxc & 1) << 7; + *p++ = 0; + *p++ = 0; + *p++ = 0; + *p++ = 0; + } } -/*! - * 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 +/* This function is responsible for generating the ECU's output + * in the event that the Radio Subsystem does not have a good + * traffic frame - conditions corresponding to BFI=1 in the specs. */ -int osmo_ecu_fr_conceal(struct osmo_ecu_fr_state *state, uint8_t *frame) +static void fr_ecu_output(struct fr_ecu_state *fr, 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; + bool mute; + + switch (fr->pr_state) { + case STATE_NO_DATA: + memcpy(frame, osmo_gsm611_silence_frame, GSM_FR_BYTES); + return; + case STATE_SPEECH: + /* TS 46.011 chapter 6: "The first lost speech frame is + * replaced at the speech decoder input by the previous + * good speech frame." */ + memcpy(frame, fr->speech_frame, GSM_FR_BYTES); + fr->pr_state = STATE_SP_MUTING; + return; + case STATE_SP_MUTING: + mute = reduce_xmaxc(fr->speech_frame); + memcpy(frame, fr->speech_frame, GSM_FR_BYTES); + random_grid_pos(fr, frame); + if (mute) + fr->pr_state = STATE_NO_DATA; + return; + case STATE_SID: + fr->sid_reemit_count++; + if (fr->sid_reemit_count >= 48) { + fr->pr_state = STATE_SID_MUTING; + reduce_xmaxc_sid(fr); + } + reemit_sid(fr, frame); + return; + case STATE_SID_MUTING: + if (reduce_xmaxc_sid(fr)) { + fr->pr_state = STATE_NO_DATA; + memcpy(frame, osmo_gsm611_silence_frame, GSM_FR_BYTES); + } else + reemit_sid(fr, frame); + return; + default: + /* a severe bug in the state machine! */ + OSMO_ASSERT(0); } - - /* 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; } /*********************************************************************** @@ -171,44 +285,57 @@ int osmo_ecu_fr_conceal(struct osmo_ecu_fr_state *state, uint8_t *frame) static struct osmo_ecu_state *ecu_fr_init(void *ctx, enum osmo_ecu_codec codec) { - struct osmo_ecu_state *st; - size_t size = sizeof(*st) + sizeof(struct osmo_ecu_fr_state); + struct fr_ecu_state *fr; - st = talloc_named_const(ctx, size, "ecu_state_FR"); - if (!st) - return NULL; + fr = talloc_zero(ctx, struct fr_ecu_state); + fr->ecu_state.codec = codec; + fr->pr_state = STATE_NO_DATA; + osmo_prbs_state_init(&fr->prng, &osmo_prbs15); - memset(st, 0, size); - st->codec = codec; + return (struct osmo_ecu_state *) fr; +} - return st; +static inline struct fr_ecu_state *_osmo_ecu_state_get_fr(struct osmo_ecu_state *st) +{ + return (struct fr_ecu_state *)container_of(st, struct fr_ecu_state, ecu_state); } static int ecu_fr_frame_in(struct osmo_ecu_state *st, bool bfi, const uint8_t *frame, unsigned int frame_bytes) { - struct osmo_ecu_fr_state *fr = (struct osmo_ecu_fr_state *) &st->data; + struct fr_ecu_state *fr = _osmo_ecu_state_get_fr(st); + if (bfi) return 0; + if (frame_bytes != GSM_FR_BYTES) + return 0; + if ((frame[0] & 0xF0) != 0xD0) + return 0; - osmo_ecu_fr_reset(fr, frame); + fr_ecu_input(fr, frame); return 0; } static int ecu_fr_frame_out(struct osmo_ecu_state *st, uint8_t *frame_out) { - struct osmo_ecu_fr_state *fr = (struct osmo_ecu_fr_state *) &st->data; + struct fr_ecu_state *fr = _osmo_ecu_state_get_fr(st); + + fr_ecu_output(fr, frame_out); + return GSM_FR_BYTES; +} + +static bool ecu_fr_is_dtx_pause(struct osmo_ecu_state *st) +{ + struct fr_ecu_state *fr = _osmo_ecu_state_get_fr(st); - if (osmo_ecu_fr_conceal(fr, frame_out) == 0) - return GSM_FR_BYTES; - else - return -1; + return fr->last_input_was_sid; } static const struct osmo_ecu_ops osmo_ecu_ops_fr = { .init = ecu_fr_init, .frame_in = ecu_fr_frame_in, .frame_out = ecu_fr_frame_out, + .is_dtx_pause = ecu_fr_is_dtx_pause, }; static __attribute__((constructor)) void on_dso_load_ecu_fr(void) |