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.

/*
 * We would like to generate our EFR RTP frame packing and unpacking code
 * using bitter and sweet utilities from libgsm, so we'll end up packing
 * and unpacking EFR just like good old FR.  However, because of our
 * slightly different approach, entering the spec file for bitter and sweet
 * manually would be tedious and error-prone, hence we are going to
 * generate it with this program.
 */

#include <stdio.h>
#include <stdlib.h>

#define	PRM_NO	57

/* table from ETSI EFR code */
static const unsigned bitno[PRM_NO] =
{
    7, 8, 9, 8, 6,                          /* LSP VQ          */
    9, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 5,  /* first subframe  */
    6, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 5,  /* second subframe */
    9, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 5,  /* third subframe  */
    6, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 5   /* fourth subframe */
};

main(argc, argv)
	char **argv;
{
	unsigned n;

	printf("EFR_MAGIC\t4\n");
	for (n = 0; n < PRM_NO; n++)
		printf("params[%u]\t%u\n", n, bitno[n]);
	exit(0);
}