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view libgsmfr2/full_dec_wrap.c @ 581:e2d5cad04cbf

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libgsmhr1 RxFE: store CN R0+LPC separately from speech In the original GSM 06.06 code the ECU for speech mode is entirely separate from the CN generator, maintaining separate state. (The main intertie between them is the speech vs CN state variable, distinguishing between speech and CN BFIs, in addition to the CN-specific function of distinguishing between initial and update SIDs.) In the present RxFE implementation I initially thought that we could use the same saved_frame buffer for both ECU and CN, overwriting just the first 4 params (R0 and LPC) when a valid SID comes in. However, I now realize it was a bad idea: the original code has a corner case (long sequence of speech-mode BFIs to put the ECU in state 6, then SID and CN-mode BFIs, then a good speech frame) that would be broken by that buffer reuse approach. We could eliminate this corner case by resetting the ECU state when passing through a CN insertion period, but doing so would needlessly increase the behavioral diffs between GSM 06.06 and our version. Solution: use a separate CN-specific buffer for CN R0+LPC parameters, and match the behavior of GSM 06.06 code in this regard.
author Mychaela Falconia <falcon@freecalypso.org>
date Thu, 13 Feb 2025 10:02:45 +0000
parents f681fb758041
children
line wrap: on
line source

/*
 * This module implements a wrapper around the main processing functions
 * of our full decoder, handling RTP input per TW-TS-001.
 */

#include <stdint.h>
#include "tw_gsmfr.h"

int gsmfr_fulldec_rtp_in(struct gsmfr_fulldec_state *st, const uint8_t *rtp_pl,
			 unsigned rtp_pl_len, int16_t *pcm)
{
	switch (rtp_pl_len) {
	case 0:
		/* BFI-no-data, but not an invalid RTP input per se */
		gsmfr_fulldec_bfi(st, 0, pcm);
		return 0;
	case 1:
		if ((rtp_pl[0] & 0xF6) != 0xE6)
			goto bad_rtp_input;
		/* TW-TS-001 No_Data frame */
		gsmfr_fulldec_bfi(st, rtp_pl[0] & 1, pcm);
		return 0;
	case GSMFR_RTP_FRAME_LEN:
		if ((rtp_pl[0] & 0xF0) != 0xD0)
			goto bad_rtp_input;
		/* basic RTP format */
		gsmfr_fulldec_good_frame(st, rtp_pl, pcm);
		return 0;
	case GSMFR_RTP_FRAME_LEN+1:
		if ((rtp_pl[0] & 0xF4) != 0xE0)
			goto bad_rtp_input;
		if ((rtp_pl[1] & 0xF0) != 0xD0)
			goto bad_rtp_input;
		/* extended RTP format (TW-TS-001) */
		if (rtp_pl[0] & 0x02)
			gsmfr_fulldec_bfi_bits(st, rtp_pl + 1, rtp_pl[0] & 1,
						pcm);
		else
			gsmfr_fulldec_good_frame(st, rtp_pl + 1, pcm);
		return 0;
	default:
	bad_rtp_input:
		/*
		 * Treat it like BFI-no-data, and tell the caller
		 * that we received an invalid RTP payload.
		 */
		gsmfr_fulldec_bfi(st, 0, pcm);
		return -1;
	}
}