view dev/efr-sid-insert.c @ 581:e2d5cad04cbf

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 3b5958f28a40
children
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/*
 * We need to implement a function that inserts the 95 bit wide SID
 * codeword into the frame, and we would like to do it more efficiently
 * than calling a "set bit" function for each of the 95 bits.  This
 * program will produce a more efficient solution.
 */

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

static const uint8_t SID_codeword_bit_idx[95] =
{
     45,  46,  48,  49,  50,  51,  52,  53,  54,  55,
     56,  57,  58,  59,  60,  61,  62,  63,  64,  65,
     66,  67,  68,  94,  95,  96,  98,  99, 100, 101,
    102, 103, 104, 105, 106, 107, 108, 109, 110, 111,
    112, 113, 114, 115, 116, 117, 118, 148, 149, 150,
    151, 152, 153, 154, 155, 156, 157, 158, 159, 160,
    161, 162, 163, 164, 165, 166, 167, 168, 169, 170,
    171, 196, 197, 198, 199, 200, 201, 202, 203, 204,
    205, 206, 207, 208, 209, 212, 213, 214, 215, 216,
    217, 218, 219, 220, 221
};

static void set_bit(uint8_t *frame, unsigned bitnum)
{
	unsigned bytenum = bitnum >> 3;
	unsigned bit_in_byte = 7 - (bitnum & 7);
	unsigned bitmask = 1 << bit_in_byte;

	frame[bytenum] |= bitmask;
}

main(argc, argv)
	char **argv;
{
	uint8_t bytes[31];
	unsigned n;

	memset(bytes, 0, 31);
	for (n = 0; n < 95; n++)
		set_bit(bytes, SID_codeword_bit_idx[n] + 4);
	for (n = 0; n < 31; n++)
		if (bytes[n])
			printf("\tframe[%u] |= 0x%02X;\n", n, bytes[n]);
	exit(0);
}