libgsmhr1 TFO: require BFI=0 and SID=0 for homing In order for a received frame to be recognized as DHF, we need not only the correct bit pattern, but also BFI=0 and SID=0. The BFI=0 requirement should be obvious, while the SID=0 requirement is needed only for HR codec. With FR and EFR, SID classification comes from the payload bits and no separate check is needed - but in HR we get an out-of-band SID ternary flag. When SID=1, no payload bits are used at all; when SID=2, we use only the first 33 bits of the payload. Therefore, it is proper to conditionalize DHF acceptance on SID=0. We already implemented this logic in the just finished full decoder; now bring TFO code into agreement.

/*
 * gsmfr_preproc_good_frame_hm() is a wrapper around gsmfr_preproc_good_frame()
 * that adds homing of the Rx DTX handler preprocessor block.  This homing
 * version of good frame preproc is not used in the full decoder (the latter
 * implements its own homing logic as specified by 3GPP), but it will be used
 * when our Rx DTX handler preprocessor functions as a TFO transform.
 */

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

void gsmfr_preproc_good_frame_hm(struct gsmfr_preproc_state *st, uint8_t *frame)
{
	if (memcmp(frame, gsmfr_decoder_homing_frame, GSMFR_RTP_FRAME_LEN))
		gsmfr_preproc_good_frame(st, frame);
	else
		gsmfr_preproc_reset(st);
}