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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 02a3c88b415d
children
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/*******************************************************************
 *
 * typedef statements of types used in all half-rate GSM routines
 *
 ******************************************************************/

#ifndef __TYPEDEFS
#define __TYPEDEFS

#include <stdint.h>

#define LW_SIGN (int32_t)0x80000000       /* sign bit */
#define LW_MIN  (int32_t)0x80000000
#define LW_MAX  (int32_t)0x7fffffff

#define SW_SIGN (int16_t)0x8000           /* sign bit for Shortword type */
#define SW_MIN  (int16_t)0x8000           /* smallest Ram */
#define SW_MAX  (int16_t)0x7fff           /* largest Ram */

/* Definition of Types *
 ***********************/

typedef int32_t Longword;              /* 32 bit "accumulator" (L_*) */
typedef int16_t Shortword;             /* 16 bit "register"  (sw*) */
typedef int16_t ShortwordRom;          /* 16 bit ROM data    (sr*) */
typedef int32_t LongwordRom;           /* 32 bit ROM data    (L_r*)  */

struct NormSw
{                                      /* normalized Shortword fractional
                                        * number snr.man precedes snr.sh (the
                                        * shift count)i */
  Shortword man;                       /* "mantissa" stored in 16 bit
                                        * location */
  Shortword sh;                        /* the shift count, stored in 16 bit
                                        * location */
};

/* Global constants *
 ********************/

#define NP 10                          /* order of the lpc filter */
#define N_SUB 4                        /* number of subframes */
#define F_LEN 160                      /* number of samples in a frame */
#define S_LEN 40                       /* number of samples in a subframe */
#define A_LEN 170                      /* LPC analysis length */
#define OS_FCTR 6                      /* maximum LTP lag oversampling
                                        * factor */

#define OVERHANG 8                     /* vad parameter */

#endif