/* Traffic channel support for Sysmocom BTS L1 */

/* (C) 2011-2012 by Harald Welte <laforge@gnumonks.org>
 *
 * All Rights Reserved
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#include <stdint.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <sys/types.h>
#include <sys/stat.h>

#include <osmocom/core/talloc.h>
#include <osmocom/core/utils.h>
#include <osmocom/core/select.h>
#include <osmocom/core/timer.h>
#include <osmocom/core/bits.h>
#include <osmocom/gsm/gsm_utils.h>
#include <osmocom/trau/osmo_ortp.h>

#include <osmo-bts/logging.h>
#include <osmo-bts/bts.h>
#include <osmo-bts/gsm_data.h>
#include <osmo-bts/msg_utils.h>
#include <osmo-bts/measurement.h>
#include <osmo-bts/amr.h>
#include <osmo-bts/l1sap.h>
#include <osmo-bts/dtx_dl_amr_fsm.h>

#include <sysmocom/femtobts/superfemto.h>
#include <sysmocom/femtobts/gsml1prim.h>
#include <sysmocom/femtobts/gsml1const.h>
#include <sysmocom/femtobts/gsml1types.h>

#include "femtobts.h"
#include "l1_if.h"

static struct msgb *l1_to_rtppayload_fr(uint8_t *l1_payload, uint8_t payload_len,
					struct gsm_lchan *lchan)
{
	struct msgb *msg;
	uint8_t *cur;

	msg = msgb_alloc_headroom(1024, 128, "L1P-to-RTP");
	if (!msg)
		return NULL;

#ifdef USE_L1_RTP_MODE
	/* new L1 can deliver bits like we need them */
	cur = msgb_put(msg, GSM_FR_BYTES);
	memcpy(cur, l1_payload, GSM_FR_BYTES);
#else
	/* step1: reverse the bit-order of each payload byte */
	osmo_revbytebits_buf(l1_payload, payload_len);

	cur = msgb_put(msg, GSM_FR_BYTES);

	/* step2: we need to shift the entire L1 payload by 4 bits right */
	osmo_nibble_shift_right(cur, l1_payload, GSM_FR_BITS/4);

	cur[0] |= 0xD0;
#endif /* USE_L1_RTP_MODE */

	lchan_set_marker(osmo_fr_check_sid(l1_payload, payload_len), lchan);

	return msg;
}

/*! \brief convert GSM-FR from RTP payload to L1 format
 *  \param[out] l1_payload payload part of L1 buffer
 *  \param[in] rtp_payload pointer to RTP payload data
 *  \param[in] payload_len length of \a rtp_payload
 *  \returns number of \a l1_payload bytes filled
 */
static int rtppayload_to_l1_fr(uint8_t *l1_payload, const uint8_t *rtp_payload,
				unsigned int payload_len)
{
#ifdef USE_L1_RTP_MODE
	/* new L1 can deliver bits like we need them */
	memcpy(l1_payload, rtp_payload, GSM_FR_BYTES);
#else
	/* step2: we need to shift the RTP payload left by one nibble*/
	osmo_nibble_shift_left_unal(l1_payload, rtp_payload, GSM_FR_BITS/4);

	/* step1: reverse the bit-order of each payload byte */
	osmo_revbytebits_buf(l1_payload, payload_len);
#endif /* USE_L1_RTP_MODE */
	return GSM_FR_BYTES;
}

#if defined(L1_HAS_EFR) && defined(USE_L1_RTP_MODE)
static struct msgb *l1_to_rtppayload_efr(uint8_t *l1_payload,
					 uint8_t payload_len,
					 struct gsm_lchan *lchan)
{
	struct msgb *msg;
	uint8_t *cur;

	msg = msgb_alloc_headroom(1024, 128, "L1P-to-RTP");
	if (!msg)
		return NULL;

#ifdef USE_L1_RTP_MODE
	/* new L1 can deliver bits like we need them */
	cur = msgb_put(msg, GSM_EFR_BYTES);
	memcpy(cur, l1_payload, GSM_EFR_BYTES);
#else
	/* step1: reverse the bit-order of each payload byte */
	osmo_revbytebits_buf(l1_payload, payload_len);

	cur = msgb_put(msg, GSM_EFR_BYTES);

	/* step 2: we need to shift the entire L1 payload by 4 bits right */
	osmo_nibble_shift_right(cur, l1_payload, GSM_EFR_BITS/4);

	cur[0] |= 0xC0;
#endif /* USE_L1_RTP_MODE */
	enum osmo_amr_type ft;
	enum osmo_amr_quality bfi;
	uint8_t cmr;
	int8_t sti, cmi;
	osmo_amr_rtp_dec(l1_payload, payload_len, &cmr, &cmi, &ft, &bfi, &sti);
	lchan_set_marker(ft == AMR_GSM_EFR_SID, lchan);

	return msg;
}

static int rtppayload_to_l1_efr(uint8_t *l1_payload, const uint8_t *rtp_payload,
				unsigned int payload_len)
{
#ifndef USE_L1_RTP_MODE
#error We don't support EFR with L1 that doesn't support RTP mode!
#else
	memcpy(l1_payload, rtp_payload, payload_len);

	return payload_len;
#endif
}
#else
#warning No EFR support in L1
#endif /* L1_HAS_EFR */

#ifdef USE_L1_RTP_MODE
/* change the bit-order of each unaligned field inside the HR codec
 * payload from little-endian bit-ordering to bit-endian and vice-versa.
 * This is required on all sysmoBTS DSP versions < 5.3.3 in order to
 * be compliant with ETSI TS 101 318 Chapter 5.2 */
static void hr_jumble(uint8_t *dst, const uint8_t *src)
{
	/* Table 2 / Section 5.2.1 of ETSI TS 101 381 */
	const int p_unvoiced[] =
		{ 5, 11,  9,  8,  1,  2,  7,  7,  5,  7,  7,  5,  7,  7,  5,  7,  7,  5 };
	/* Table 3 / Section 5.2.1 of ETSI TS 101 381 */
	const int p_voiced[] =
		{ 5, 11,  9,  8,  1,  2,  8,  9,  5,  4,  9,  5,  4,  9,  5,  4,  9,  5 };

	int base, i, j, l, si, di;
	const int *p;

	memset(dst, 0x00, GSM_HR_BYTES);

	p = (src[4] & 0x30) ? p_voiced : p_unvoiced;

	base = 0;
	for (i = 0; i < 18; i++) {
		l = p[i];
		for (j = 0; j < l; j++) {
			si = base + j;
			di = base + l - j - 1;

			if (src[si >> 3] & (1 << (7 - (si & 7))))
				dst[di >> 3] |= (1 << (7 - (di & 7)));
		}

		base += l;
	}
}
#endif /* USE_L1_RTP_MODE */

static struct msgb *l1_to_rtppayload_hr(uint8_t *l1_payload, uint8_t payload_len,
					struct gsm_lchan *lchan)
{
	struct msgb *msg;
	uint8_t *cur;

	msg = msgb_alloc_headroom(1024, 128, "L1P-to-RTP");
	if (!msg)
		return NULL;

	if (payload_len != GSM_HR_BYTES) {
		LOGP(DL1P, LOGL_ERROR, "L1 HR frame length %u != expected %u\n",
			payload_len, GSM_HR_BYTES);
		return NULL;
	}

	cur = msgb_put(msg, GSM_HR_BYTES);
#ifdef USE_L1_RTP_MODE
	struct femtol1_hdl *fl1h = trx_femtol1_hdl(lchan->ts->trx);
	if (fl1h->rtp_hr_jumble_needed)
		hr_jumble(cur, l1_payload);
	else
		memcpy(cur, l1_payload, GSM_HR_BYTES);
#else /* USE_L1_RTP_MODE */
	memcpy(cur, l1_payload, GSM_HR_BYTES);
	/* reverse the bit-order of each payload byte */
	osmo_revbytebits_buf(cur, GSM_HR_BYTES);
#endif /* USE_L1_RTP_MODE */

	lchan_set_marker(osmo_hr_check_sid(l1_payload, payload_len), lchan);

	return msg;
}

/*! \brief convert GSM-FR from RTP payload to L1 format
 *  \param[out] l1_payload payload part of L1 buffer
 *  \param[in] rtp_payload pointer to RTP payload data
 *  \param[in] payload_len length of \a rtp_payload
 *  \returns number of \a l1_payload bytes filled
 */
static int rtppayload_to_l1_hr(uint8_t *l1_payload, const uint8_t *rtp_payload,
				unsigned int payload_len, struct gsm_lchan *lchan)
{

	if (payload_len != GSM_HR_BYTES) {
		LOGP(DL1P, LOGL_ERROR, "RTP HR frame length %u != expected %u\n",
			payload_len, GSM_HR_BYTES);
		return 0;
	}

#ifdef USE_L1_RTP_MODE
	struct femtol1_hdl *fl1h = trx_femtol1_hdl(lchan->ts->trx);
	if (fl1h->rtp_hr_jumble_needed)
		hr_jumble(l1_payload, rtp_payload);
	else
		memcpy(l1_payload, rtp_payload, GSM_HR_BYTES);
#else /* USE_L1_RTP_MODE */
	memcpy(l1_payload, rtp_payload, GSM_HR_BYTES);
	/* reverse the bit-order of each payload byte */
	osmo_revbytebits_buf(l1_payload, GSM_HR_BYTES);
#endif /* USE_L1_RTP_MODE */

	return GSM_HR_BYTES;
}

static struct msgb *l1_to_rtppayload_amr(uint8_t *l1_payload, uint8_t payload_len,
					 struct gsm_lchan *lchan)
{
#ifndef USE_L1_RTP_MODE
	struct amr_multirate_conf *amr_mrc = &lchan->tch.amr_mr;
#endif
	struct msgb *msg;
	uint8_t amr_if2_len = payload_len - 2;
	uint8_t *cur;

	msg = msgb_alloc_headroom(1024, 128, "L1P-to-RTP");
	if (!msg)
		return NULL;

#ifdef USE_L1_RTP_MODE
	cur = msgb_put(msg, amr_if2_len);
	memcpy(cur, l1_payload+2, amr_if2_len);

	/*
	 * Audiocode's MGW doesn't like receiving CMRs that are not
	 * the same as the previous one. This means we need to patch
	 * the content here.
	 */
	if ((cur[0] & 0xF0) == 0xF0)
		cur[0]= lchan->tch.last_cmr << 4;
	else
		lchan->tch.last_cmr = cur[0] >> 4;
#else
	u_int8_t cmr;
	uint8_t ft = l1_payload[2] & 0xF;
	uint8_t cmr_idx = l1_payload[1];
	/* CMR == Unset means CMR was not transmitted at this TDMA */
	if (cmr_idx == GsmL1_AmrCodecMode_Unset)
		cmr = lchan->tch.last_cmr;
	else if (cmr_idx >= amr_mrc->num_modes ||
		 cmr_idx > GsmL1_AmrCodecMode_Unset) {
		/* Make sure the CMR of the phone is in the active codec set */
		LOGP(DL1P, LOGL_NOTICE, "L1->RTP: overriding CMR IDX %u\n", cmr_idx);
		cmr = AMR_CMR_NONE;
	} else {
		cmr = amr_mrc->bts_mode[cmr_idx].mode;
		lchan->tch.last_cmr = cmr;
	}

	/* RFC 3267  4.4.1 Payload Header */
	msgb_put_u8(msg, (cmr << 4));

	/* RFC 3267  AMR TOC */
	msgb_put_u8(msg, AMR_TOC_QBIT | (ft << 3));

	cur = msgb_put(msg, amr_if2_len-1);

	/* step1: reverse the bit-order within every byte */
	osmo_revbytebits_buf(l1_payload+2, amr_if2_len);

	/* step2: shift everything left by one nibble */
	osmo_nibble_shift_left_unal(cur, l1_payload+2, amr_if2_len*2 -1);

#endif /* USE_L1_RTP_MODE */

	return msg;
}

/*! \brief convert AMR from RTP payload to L1 format
 *  \param[out] l1_payload payload part of L1 buffer
 *  \param[in] rtp_payload pointer to RTP payload data
 *  \param[in] payload_len length of \a rtp_payload
 *  \returns number of \a l1_payload bytes filled
 */
static int rtppayload_to_l1_amr(uint8_t *l1_payload, const uint8_t *rtp_payload,
				uint8_t payload_len, uint8_t ft)
{
#ifdef USE_L1_RTP_MODE
	memcpy(l1_payload, rtp_payload, payload_len);
#else
	uint8_t amr_if2_core_len = payload_len - 2;

	/* step1: shift everything right one nibble; make space for FT */
	osmo_nibble_shift_right(l1_payload+2, rtp_payload+2, amr_if2_core_len*2);
	/* step2: reverse the bit-order within every byte of the IF2
	 * core frame contained in the RTP payload */
	osmo_revbytebits_buf(l1_payload+2, amr_if2_core_len+1);

	/* lower 4 bit of first FR2 byte contains FT */
	l1_payload[2] |= ft;
#endif /* USE_L1_RTP_MODE */
	return payload_len;
}

#define RTP_MSGB_ALLOC_SIZE	512

/*! \brief function for incoming RTP via TCH.req
 *  \param[in] rtp_pl buffer containing RTP payload
 *  \param[in] rtp_pl_len length of \a rtp_pl
 *  \param[in] use_cache Use cached payload instead of parsing RTP
 *  \param[in] marker RTP header Marker bit (indicates speech onset)
 *  \returns 0 if encoding result can be sent further to L1 without extra actions
 *           positive value if data is ready AND extra actions are required
 *           negative value otherwise (no data for L1 encoded)
 *
 * This function prepares a msgb with a L1 PH-DATA.req primitive and
 * queues it into lchan->dl_tch_queue.
 *
 * Note that the actual L1 primitive header is not fully initialized
 * yet, as things like the frame number, etc. are unknown at the time we
 * pre-fill the primtive.
 */
int l1if_tch_encode(struct gsm_lchan *lchan, uint8_t *data, uint8_t *len,
		    const uint8_t *rtp_pl, unsigned int rtp_pl_len, uint32_t fn,
		    bool use_cache, bool marker)
{
	uint8_t *payload_type;
	uint8_t *l1_payload, ft;
	int rc = 0;
	bool is_sid = false;

	DEBUGP(DRTP, "%s RTP IN: %s\n", gsm_lchan_name(lchan),
		osmo_hexdump(rtp_pl, rtp_pl_len));

	payload_type = &data[0];
	l1_payload = &data[1];

	switch (lchan->tch_mode) {
	case GSM48_CMODE_SPEECH_V1:
		if (lchan->type == GSM_LCHAN_TCH_F) {
			*payload_type = GsmL1_TchPlType_Fr;
			rc = rtppayload_to_l1_fr(l1_payload,
						 rtp_pl, rtp_pl_len);
			if (rc && lchan->ts->trx->bts->dtxd)
				is_sid = osmo_fr_check_sid(rtp_pl, rtp_pl_len);
		} else{
			*payload_type = GsmL1_TchPlType_Hr;
			rc = rtppayload_to_l1_hr(l1_payload,
						 rtp_pl, rtp_pl_len, lchan);
			if (rc && lchan->ts->trx->bts->dtxd)
				is_sid = osmo_hr_check_sid(rtp_pl, rtp_pl_len);
		}
		if (is_sid)
			dtx_cache_payload(lchan, rtp_pl, rtp_pl_len, fn, -1);
		break;
#if defined(L1_HAS_EFR) && defined(USE_L1_RTP_MODE)
	case GSM48_CMODE_SPEECH_EFR:
		*payload_type = GsmL1_TchPlType_Efr;
		rc = rtppayload_to_l1_efr(l1_payload, rtp_pl,
					  rtp_pl_len);
		/* FIXME: detect and save EFR SID */
		break;
#endif
	case GSM48_CMODE_SPEECH_AMR:
		if (use_cache) {
			*payload_type = GsmL1_TchPlType_Amr;
			rtppayload_to_l1_amr(l1_payload, lchan->tch.dtx.cache,
					     lchan->tch.dtx.len, ft);
			*len = lchan->tch.dtx.len + 1;
			return 0;
		}

		rc = dtx_dl_amr_fsm_step(lchan, rtp_pl, rtp_pl_len, fn,
					 l1_payload, marker, len, &ft);
		if (rc < 0)
			return rc;
		if (!dtx_dl_amr_enabled(lchan)) {
			*payload_type = GsmL1_TchPlType_Amr;
			rtppayload_to_l1_amr(l1_payload + 2, rtp_pl, rtp_pl_len,
					     ft);
			return 0;
		}

		/* DTX DL-specific logic below: */
		switch (lchan->tch.dtx.dl_amr_fsm->state) {
		case ST_ONSET_V:
			*payload_type = GsmL1_TchPlType_Amr_Onset;
			dtx_cache_payload(lchan, rtp_pl, rtp_pl_len, fn, 0);
			*len = 3;
			return 1;
		case ST_VOICE:
			*payload_type = GsmL1_TchPlType_Amr;
			rtppayload_to_l1_amr(l1_payload + 2, rtp_pl, rtp_pl_len,
					     ft);
			return 0;
		case ST_SID_F1:
			if (lchan->type == GSM_LCHAN_TCH_H) { /* AMR HR */
				*payload_type = GsmL1_TchPlType_Amr_SidFirstP1;
				rtppayload_to_l1_amr(l1_payload + 2, rtp_pl,
						     rtp_pl_len, ft);
				return 0;
			}
			/* AMR FR */
			*payload_type = GsmL1_TchPlType_Amr;
			rtppayload_to_l1_amr(l1_payload + 2, rtp_pl, rtp_pl_len,
					     ft);
			return 0;
		case ST_SID_F2:
			*payload_type = GsmL1_TchPlType_Amr;
			rtppayload_to_l1_amr(l1_payload + 2, rtp_pl, rtp_pl_len,
					     ft);
			return 0;
		case ST_F1_INH_V:
			*payload_type = GsmL1_TchPlType_Amr_SidFirstInH;
			*len = 3;
			dtx_cache_payload(lchan, rtp_pl, rtp_pl_len, fn, 0);
			return 1;
		case ST_U_INH_V:
			*payload_type = GsmL1_TchPlType_Amr_SidUpdateInH;
			*len = 3;
			dtx_cache_payload(lchan, rtp_pl, rtp_pl_len, fn, 0);
			return 1;
		case ST_SID_U:
		case ST_U_NOINH:
			return -EAGAIN;
		case ST_FACCH:
			return -EBADMSG;
		default:
			LOGP(DRTP, LOGL_ERROR, "Unhandled DTX DL AMR FSM state "
			     "%d\n", lchan->tch.dtx.dl_amr_fsm->state);
			return -EINVAL;
		}
		break;
	default:
		/* we don't support CSD modes */
		rc = -1;
		break;
	}

	if (rc < 0) {
		LOGP(DRTP, LOGL_ERROR, "%s unable to parse RTP payload\n",
		     gsm_lchan_name(lchan));
		return -EBADMSG;
	}

	*len = rc + 1;

	DEBUGP(DRTP, "%s RTP->L1: %s\n", gsm_lchan_name(lchan),
		osmo_hexdump(data, *len));
	return 0;
}

static int is_recv_only(uint8_t speech_mode)
{
	return (speech_mode & 0xF0) == (1 << 4);
}

/*! \brief receive a traffic L1 primitive for a given lchan */
int l1if_tch_rx(struct gsm_bts_trx *trx, uint8_t chan_nr, struct msgb *l1p_msg)
{
	GsmL1_Prim_t *l1p = msgb_l1prim(l1p_msg);
	GsmL1_PhDataInd_t *data_ind = &l1p->u.phDataInd;
	uint8_t *payload, payload_type, payload_len, sid_first[9] = { 0 };
	struct msgb *rmsg = NULL;
	struct gsm_lchan *lchan = &trx->ts[L1SAP_CHAN2TS(chan_nr)].lchan[l1sap_chan2ss(chan_nr)];

	if (is_recv_only(lchan->abis_ip.speech_mode))
		return -EAGAIN;

	if (data_ind->msgUnitParam.u8Size < 1) {
		LOGPFN(DL1P, LOGL_DEBUG, data_ind->u32Fn, "chan_nr %d Rx Payload size 0\n", chan_nr);
		/* Push empty payload to upper layers */
		rmsg = msgb_alloc_headroom(256, 128, "L1P-to-RTP");
		return add_l1sap_header(trx, rmsg, lchan, chan_nr, data_ind->u32Fn,
					data_ind->measParam.fBer * 10000,
					data_ind->measParam.fLinkQuality * 10);
	}

	payload_type = data_ind->msgUnitParam.u8Buffer[0];
	payload = data_ind->msgUnitParam.u8Buffer + 1;
	payload_len = data_ind->msgUnitParam.u8Size - 1;

	switch (payload_type) {
	case GsmL1_TchPlType_Fr:
#if defined(L1_HAS_EFR) && defined(USE_L1_RTP_MODE)
	case GsmL1_TchPlType_Efr:
#endif
		if (lchan->type != GSM_LCHAN_TCH_F)
			goto err_payload_match;
		break;
	case GsmL1_TchPlType_Hr:
		if (lchan->type != GSM_LCHAN_TCH_H)
			goto err_payload_match;
		break;
	case GsmL1_TchPlType_Amr:
		if (lchan->type != GSM_LCHAN_TCH_H &&
		    lchan->type != GSM_LCHAN_TCH_F)
			goto err_payload_match;
		break;
	case GsmL1_TchPlType_Amr_Onset:
		if (lchan->type != GSM_LCHAN_TCH_H &&
		    lchan->type != GSM_LCHAN_TCH_F)
			goto err_payload_match;
		/* according to 3GPP TS 26.093 ONSET frames precede the first
		   speech frame of a speech burst - set the marker for next RTP
		   frame */
		lchan->rtp_tx_marker = true;
		break;
	case GsmL1_TchPlType_Amr_SidFirstP1:
		if (lchan->type != GSM_LCHAN_TCH_H)
			goto err_payload_match;
		LOGPFN(DL1P, LOGL_DEBUG, data_ind->u32Fn, "DTX: received SID_FIRST_P1 from L1 "
		     "(%d bytes)\n", payload_len);
		break;
	case GsmL1_TchPlType_Amr_SidFirstP2:
		if (lchan->type != GSM_LCHAN_TCH_H)
			goto err_payload_match;
		LOGPFN(DL1P, LOGL_DEBUG, data_ind->u32Fn, "DTX: received SID_FIRST_P2 from L1 "
		     "(%d bytes)\n", payload_len);
		break;
	case GsmL1_TchPlType_Amr_SidFirstInH:
		if (lchan->type != GSM_LCHAN_TCH_H)
			goto err_payload_match;
		lchan->rtp_tx_marker = true;
		LOGPFN(DL1P, LOGL_DEBUG, data_ind->u32Fn, "DTX: received SID_FIRST_INH from L1 "
		     "(%d bytes)\n", payload_len);
		break;
	case GsmL1_TchPlType_Amr_SidUpdateInH:
		if (lchan->type != GSM_LCHAN_TCH_H)
			goto err_payload_match;
		lchan->rtp_tx_marker = true;
		LOGPFN(DL1P, LOGL_DEBUG, data_ind->u32Fn, "DTX: received SID_UPDATE_INH from L1 "
		     "(%d bytes)\n", payload_len);
		break;
	default:
		LOGPFN(DL1P, LOGL_NOTICE, data_ind->u32Fn, "%s Rx Payload Type %s is unsupported\n",
			gsm_lchan_name(lchan),
			get_value_string(femtobts_tch_pl_names, payload_type));
		break;
	}


	switch (payload_type) {
	case GsmL1_TchPlType_Fr:
		rmsg = l1_to_rtppayload_fr(payload, payload_len, lchan);
		break;
	case GsmL1_TchPlType_Hr:
		rmsg = l1_to_rtppayload_hr(payload, payload_len, lchan);
		break;
#if defined(L1_HAS_EFR) && defined(USE_L1_RTP_MODE)
	case GsmL1_TchPlType_Efr:
		rmsg = l1_to_rtppayload_efr(payload, payload_len, lchan);
		break;
#endif
	case GsmL1_TchPlType_Amr:
		rmsg = l1_to_rtppayload_amr(payload, payload_len, lchan);
		break;
	case GsmL1_TchPlType_Amr_SidFirstP1:
		memcpy(sid_first, payload, payload_len);
		int len = osmo_amr_rtp_enc(sid_first, 0, AMR_SID, AMR_GOOD);
		if (len < 0)
			return 0;
		rmsg = l1_to_rtppayload_amr(sid_first, len, lchan);
		break;
	/* FIXME: what about GsmL1_TchPlType_Amr_SidBad? not well documented. */
	}

	if (rmsg)
		return add_l1sap_header(trx, rmsg, lchan, chan_nr, data_ind->u32Fn,
					data_ind->measParam.fBer * 10000,
					data_ind->measParam.fLinkQuality * 10);

	return 0;

err_payload_match:
	LOGPFN(DL1P, LOGL_ERROR, data_ind->u32Fn, "%s Rx Payload Type %s incompatible with lchan\n",
		gsm_lchan_name(lchan),
		get_value_string(femtobts_tch_pl_names, payload_type));
	return -EINVAL;
}

struct msgb *gen_empty_tch_msg(struct gsm_lchan *lchan, uint32_t fn)
{
	struct msgb *msg;
	GsmL1_Prim_t *l1p;
	GsmL1_PhDataReq_t *data_req;
	GsmL1_MsgUnitParam_t *msu_param;
	uint8_t *payload_type;
	uint8_t *l1_payload;
	int rc;

	msg = l1p_msgb_alloc();
	if (!msg)
		return NULL;

	l1p = msgb_l1prim(msg);
	data_req = &l1p->u.phDataReq;
	msu_param = &data_req->msgUnitParam;
	payload_type = &msu_param->u8Buffer[0];
	l1_payload = &msu_param->u8Buffer[1];

	switch (lchan->tch_mode) {
	case GSM48_CMODE_SPEECH_AMR:
		if (lchan->type == GSM_LCHAN_TCH_H &&
		    dtx_dl_amr_enabled(lchan)) {
			/* we have to explicitly handle sending SID FIRST P2 for
			   AMR HR in here */
			*payload_type = GsmL1_TchPlType_Amr_SidFirstP2;
			rc = dtx_dl_amr_fsm_step(lchan, NULL, 0, fn, l1_payload,
						 false, &(msu_param->u8Size),
						 NULL);
			if (rc == 0)
				return msg;
		}
		*payload_type = GsmL1_TchPlType_Amr;
		break;
	case GSM48_CMODE_SPEECH_V1:
		if (lchan->type == GSM_LCHAN_TCH_F)
			*payload_type = GsmL1_TchPlType_Fr;
		else
			*payload_type = GsmL1_TchPlType_Hr;
		break;
	case GSM48_CMODE_SPEECH_EFR:
		*payload_type = GsmL1_TchPlType_Efr;
		break;
	default:
		msgb_free(msg);
		return NULL;
	}

	rc = repeat_last_sid(lchan, l1_payload, fn);
	if (!rc) {
		msgb_free(msg);
		return NULL;
	}
	msu_param->u8Size = rc;

	return msg;
}
