From d5bbd8ccf79eaf13bc23cc71accbeb3ff638b6dd Mon Sep 17 00:00:00 2001
From: Harald Welte <laforge@gnumonks.org>
Date: Mon, 19 Feb 2018 14:21:36 +0100
Subject: trx/scheduler: Use integer math for TOA (Timing of Arrival)

There's no need to express TOA as a float:
* We receive it as signed 16bit integer in units 1/256 symbol periods
* We pass it to L1SAP as signed integer in 1/4 symbol periods

So turn it into an int16_t with 1/256 symbol period accuracy throughout
the code to avoid both float arithmetic as well as loosing any precision.

Change-Id: Idce4178e0b1f7e940ebc22b3e2f340fcd544d4ec
---
 include/osmo-bts/scheduler.h             |  6 ++--
 include/osmo-bts/scheduler_backend.h     | 12 +++----
 src/common/scheduler.c                   |  4 +--
 src/osmo-bts-trx/l1_if.c                 | 12 +++----
 src/osmo-bts-trx/l1_if.h                 |  2 +-
 src/osmo-bts-trx/loops.c                 | 31 +++++++++---------
 src/osmo-bts-trx/loops.h                 |  2 +-
 src/osmo-bts-trx/scheduler_trx.c         | 54 ++++++++++++++++----------------
 src/osmo-bts-trx/trx_if.c                | 12 +++----
 src/osmo-bts-virtual/scheduler_virtbts.c | 10 +++---
 10 files changed, 74 insertions(+), 71 deletions(-)

diff --git a/include/osmo-bts/scheduler.h b/include/osmo-bts/scheduler.h
index 4d34315f..98f38d39 100644
--- a/include/osmo-bts/scheduler.h
+++ b/include/osmo-bts/scheduler.h
@@ -75,7 +75,7 @@ struct l1sched_chan_state {
 	uint8_t			rssi_num;	/* number of RSSI values */
 	float			rssi_sum;	/* sum of RSSI values */
 	uint8_t			toa_num;	/* number of TOA values */
-	float			toa_sum;	/* sum of TOA values */
+	int32_t			toa256_sum;	/* sum of TOA values (1/256 symbol) */
 
 	/* loss detection */
 	uint8_t			lost;		/* (SACCH) loss detection */
@@ -113,7 +113,7 @@ struct l1sched_chan_state {
 		int		rssi_count;	/* received RSSI values */
 		int		rssi_valid_count; /* number of stored value */
 		int		rssi_got_burst; /* any burst received so far */
-		float		toa_sum;	/* sum of TOA values */
+		int32_t		toa256_sum;	/* sum of TOA values (1/256 symbol) */
 		int		toa_num;	/* number of TOA value */
 	} meas;
 
@@ -165,7 +165,7 @@ int trx_sched_clock(struct gsm_bts *bts, uint32_t fn);
 
 /*! \brief handle an UL burst received by PHY */
 int trx_sched_ul_burst(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
-        sbit_t *bits, uint16_t nbits, int8_t rssi, float toa);
+        sbit_t *bits, uint16_t nbits, int8_t rssi, int16_t toa);
 
 /*! \brief set multiframe scheduler to given physical channel config */
 int trx_sched_set_pchan(struct l1sched_trx *l1t, uint8_t tn,
diff --git a/include/osmo-bts/scheduler_backend.h b/include/osmo-bts/scheduler_backend.h
index 5e077eff..5f11f9bc 100644
--- a/include/osmo-bts/scheduler_backend.h
+++ b/include/osmo-bts/scheduler_backend.h
@@ -16,7 +16,7 @@ typedef ubit_t *trx_sched_dl_func(struct l1sched_trx *l1t, uint8_t tn,
 typedef int trx_sched_ul_func(struct l1sched_trx *l1t, uint8_t tn,
 			      uint32_t fn, enum trx_chan_type chan,
 			      uint8_t bid, sbit_t *bits, uint16_t nbits,
-			      int8_t rssi, float toa);
+			      int8_t rssi, int16_t toa256);
 
 struct trx_chan_desc {
 	/*! \brief Is this on a PDCH (PS) ? */
@@ -74,19 +74,19 @@ ubit_t *tx_tchh_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, uint16_t *nbits);
 int rx_rach_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa);
+	int8_t rssi, int16_t toa256);
 int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa);
+	int8_t rssi, int16_t toa256);
 int rx_pdtch_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa);
+	int8_t rssi, int16_t toa256);
 int rx_tchf_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa);
+	int8_t rssi, int16_t toa256);
 int rx_tchh_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa);
+	int8_t rssi, int16_t toa256);
 
 const ubit_t *_sched_dl_burst(struct l1sched_trx *l1t, uint8_t tn,
 			      uint32_t fn, uint16_t *nbits);
diff --git a/src/common/scheduler.c b/src/common/scheduler.c
index e6cf541d..edd99d26 100644
--- a/src/common/scheduler.c
+++ b/src/common/scheduler.c
@@ -846,7 +846,7 @@ no_data:
 
 /* process uplink burst */
 int trx_sched_ul_burst(struct l1sched_trx *l1t, uint8_t tn, uint32_t current_fn,
-	sbit_t *bits, uint16_t nbits, int8_t rssi, float toa)
+	sbit_t *bits, uint16_t nbits, int8_t rssi, int16_t toa256)
 {
 	struct l1sched_ts *l1ts = l1sched_trx_get_ts(l1t, tn);
 	struct l1sched_chan_state *l1cs;
@@ -907,7 +907,7 @@ int trx_sched_ul_burst(struct l1sched_trx *l1t, uint8_t tn, uint32_t current_fn,
 				}
 			}
 
-			func(l1t, tn, fn, chan, bid, bits, nbits, rssi, toa);
+			func(l1t, tn, fn, chan, bid, bits, nbits, rssi, toa256);
 		} else if (chan != TRXC_RACH && !l1cs->ho_rach_detect) {
 			sbit_t spare[GSM_BURST_LEN];
 			memset(spare, 0, GSM_BURST_LEN);
diff --git a/src/osmo-bts-trx/l1_if.c b/src/osmo-bts-trx/l1_if.c
index a5fbf5ca..4d2558c8 100644
--- a/src/osmo-bts-trx/l1_if.c
+++ b/src/osmo-bts-trx/l1_if.c
@@ -487,7 +487,7 @@ int l1if_mph_time_ind(struct gsm_bts *bts, uint32_t fn)
 }
 
 
-static void l1if_fill_meas_res(struct osmo_phsap_prim *l1sap, uint8_t chan_nr, float ta,
+static void l1if_fill_meas_res(struct osmo_phsap_prim *l1sap, uint8_t chan_nr, int16_t toa256,
 	float ber, float rssi, uint32_t fn)
 {
 	memset(l1sap, 0, sizeof(*l1sap));
@@ -495,14 +495,14 @@ static void l1if_fill_meas_res(struct osmo_phsap_prim *l1sap, uint8_t chan_nr, f
 		PRIM_OP_INDICATION, NULL);
 	l1sap->u.info.type = PRIM_INFO_MEAS;
 	l1sap->u.info.u.meas_ind.chan_nr = chan_nr;
-	l1sap->u.info.u.meas_ind.ta_offs_qbits = (int16_t)(ta*4);
+	l1sap->u.info.u.meas_ind.ta_offs_qbits = toa256/64;
 	l1sap->u.info.u.meas_ind.ber10k = (unsigned int) (ber * 10000);
 	l1sap->u.info.u.meas_ind.inv_rssi = (uint8_t) (rssi * -1);
 	l1sap->u.info.u.meas_ind.fn = fn;
 }
 
 int l1if_process_meas_res(struct gsm_bts_trx *trx, uint8_t tn, uint32_t fn, uint8_t chan_nr,
-	int n_errors, int n_bits_total, float rssi, float toa)
+	int n_errors, int n_bits_total, float rssi, int16_t toa256)
 {
 	struct gsm_lchan *lchan = &trx->ts[tn].lchan[l1sap_chan2ss(chan_nr)];
 	struct osmo_phsap_prim l1sap;
@@ -510,11 +510,11 @@ int l1if_process_meas_res(struct gsm_bts_trx *trx, uint8_t tn, uint32_t fn, uint
 	float ber = n_bits_total==0 ? 1.0 : (float)n_errors / (float)n_bits_total;
 
 	LOGPFN(DMEAS, LOGL_DEBUG, fn, "RX L1 frame %s fn=%u chan_nr=0x%02x MS pwr=%ddBm rssi=%.1f dBFS "
-		"ber=%.2f%% (%d/%d bits) L1_ta=%d rqd_ta=%d toa=%.2f\n",
+		"ber=%.2f%% (%d/%d bits) L1_ta=%d rqd_ta=%d toa256=%d\n",
 		gsm_lchan_name(lchan), fn, chan_nr, ms_pwr_dbm(lchan->ts->trx->bts->band, lchan->ms_power_ctrl.current),
-		rssi, ber*100, n_errors, n_bits_total, lchan->meas.l1_info[1], lchan->rqd_ta, toa);
+		rssi, ber*100, n_errors, n_bits_total, lchan->meas.l1_info[1], lchan->rqd_ta, toa256);
 
-	l1if_fill_meas_res(&l1sap, chan_nr, lchan->rqd_ta + toa, ber, rssi, fn);
+	l1if_fill_meas_res(&l1sap, chan_nr, toa256, ber, rssi, fn);
 
 	return l1sap_up(trx, &l1sap);
 }
diff --git a/src/osmo-bts-trx/l1_if.h b/src/osmo-bts-trx/l1_if.h
index 1974efcc..77c5936c 100644
--- a/src/osmo-bts-trx/l1_if.h
+++ b/src/osmo-bts-trx/l1_if.h
@@ -69,7 +69,7 @@ int l1if_provision_transceiver_trx(struct trx_l1h *l1h);
 int l1if_provision_transceiver(struct gsm_bts *bts);
 int l1if_mph_time_ind(struct gsm_bts *bts, uint32_t fn);
 int l1if_process_meas_res(struct gsm_bts_trx *trx, uint8_t tn, uint32_t fn, uint8_t chan_nr,
-	int n_errors, int n_bits_total, float rssi, float toa);
+	int n_errors, int n_bits_total, float rssi, int16_t toa256);
 
 static inline struct l1sched_trx *trx_l1sched_hdl(struct gsm_bts_trx *trx)
 {
diff --git a/src/osmo-bts-trx/loops.c b/src/osmo-bts-trx/loops.c
index 6f87cd1f..a959a71e 100644
--- a/src/osmo-bts-trx/loops.c
+++ b/src/osmo-bts-trx/loops.c
@@ -166,12 +166,15 @@ static int ms_power_clock(struct gsm_lchan *lchan,
 }
 
 
+/* 90% of one bit duration in 1/256 symbols: 256*0.9 */
+#define TOA256_9OPERCENT	230
+
 /*
  * Timing Advance loop
  */
 
 int ta_val(struct gsm_lchan *lchan, uint8_t chan_nr,
-	struct l1sched_chan_state *chan_state, float toa)
+	struct l1sched_chan_state *chan_state, int16_t toa256)
 {
 	struct gsm_bts_trx *trx = lchan->ts->trx;
 
@@ -180,39 +183,39 @@ int ta_val(struct gsm_lchan *lchan, uint8_t chan_nr,
 		return 0;
 
 	/* sum measurement */
-	chan_state->meas.toa_sum += toa;
+	chan_state->meas.toa256_sum += toa256;
 	if (++(chan_state->meas.toa_num) < 16)
 		return 0;
 
 	/* complete set */
-	toa = chan_state->meas.toa_sum / chan_state->meas.toa_num;
+	toa256 = chan_state->meas.toa256_sum / chan_state->meas.toa_num;
 
 	/* check for change of TOA */
-	if (toa < -0.9F && lchan->rqd_ta > 0) {
+	if (toa256 < -TOA256_9OPERCENT && lchan->rqd_ta > 0) {
 		LOGP(DLOOP, LOGL_INFO, "TOA of trx=%u chan_nr=0x%02x is too "
-			"early (%.2f), now lowering TA from %d to %d\n",
-			trx->nr, chan_nr, toa, lchan->rqd_ta,
+			"early (%d), now lowering TA from %d to %d\n",
+			trx->nr, chan_nr, toa256, lchan->rqd_ta,
 			lchan->rqd_ta - 1);
 		lchan->rqd_ta--;
-	} else if (toa > 0.9F && lchan->rqd_ta < 63) {
+	} else if (toa256 > TOA256_9OPERCENT && lchan->rqd_ta < 63) {
 		LOGP(DLOOP, LOGL_INFO, "TOA of trx=%u chan_nr=0x%02x is too "
-			"late (%.2f), now raising TA from %d to %d\n",
-			trx->nr, chan_nr, toa, lchan->rqd_ta,
+			"late (%d), now raising TA from %d to %d\n",
+			trx->nr, chan_nr, toa256, lchan->rqd_ta,
 			lchan->rqd_ta + 1);
 		lchan->rqd_ta++;
 	} else
 		LOGP(DLOOP, LOGL_INFO, "TOA of trx=%u chan_nr=0x%02x is "
-			"correct (%.2f), keeping current TA of %d\n",
-			trx->nr, chan_nr, toa, lchan->rqd_ta);
+			"correct (%d), keeping current TA of %d\n",
+			trx->nr, chan_nr, toa256, lchan->rqd_ta);
 
 	chan_state->meas.toa_num = 0;
-	chan_state->meas.toa_sum = 0;
+	chan_state->meas.toa256_sum = 0;
 
 	return 0;
 }
 
 int trx_loop_sacch_input(struct l1sched_trx *l1t, uint8_t chan_nr,
-	struct l1sched_chan_state *chan_state, int8_t rssi, float toa)
+	struct l1sched_chan_state *chan_state, int8_t rssi, int16_t toa256)
 {
 	struct gsm_lchan *lchan = &l1t->trx->ts[L1SAP_CHAN2TS(chan_nr)]
 					.lchan[l1sap_chan2ss(chan_nr)];
@@ -222,7 +225,7 @@ int trx_loop_sacch_input(struct l1sched_trx *l1t, uint8_t chan_nr,
 		ms_power_val(chan_state, rssi);
 
 	if (pinst->phy_link->u.osmotrx.trx_ta_loop)
-		ta_val(lchan, chan_nr, chan_state, toa);
+		ta_val(lchan, chan_nr, chan_state, toa256);
 
 	return 0;
 }
diff --git a/src/osmo-bts-trx/loops.h b/src/osmo-bts-trx/loops.h
index 230cd4fa..f9e69c84 100644
--- a/src/osmo-bts-trx/loops.h
+++ b/src/osmo-bts-trx/loops.h
@@ -14,7 +14,7 @@
  */
 
 int trx_loop_sacch_input(struct l1sched_trx *l1t, uint8_t chan_nr,
-	struct l1sched_chan_state *chan_state, int8_t rssi, float toa);
+	struct l1sched_chan_state *chan_state, int8_t rssi, int16_t toa);
 
 int trx_loop_sacch_clock(struct l1sched_trx *l1t, uint8_t chan_nr,
         struct l1sched_chan_state *chan_state);
diff --git a/src/osmo-bts-trx/scheduler_trx.c b/src/osmo-bts-trx/scheduler_trx.c
index 43cc30b0..cefde072 100644
--- a/src/osmo-bts-trx/scheduler_trx.c
+++ b/src/osmo-bts-trx/scheduler_trx.c
@@ -714,7 +714,7 @@ send_burst:
 
 int rx_rach_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	uint8_t chan_nr;
 	struct osmo_phsap_prim l1sap;
@@ -724,7 +724,7 @@ int rx_rach_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 
 	chan_nr = trx_chan_desc[chan].chan_nr | tn;
 
-	LOGL1S(DL1P, LOGL_DEBUG, l1t, tn, chan, fn, "Received RACH toa=%.2f\n", toa);
+	LOGL1S(DL1P, LOGL_DEBUG, l1t, tn, chan, fn, "Received RACH toa=%d\n", toa256);
 
 	/* decode */
 	rc = gsm0503_rach_decode_ber(&ra, bits + 8 + 41, l1t->trx->bts->bsic, &n_errors, &n_bits_total);
@@ -742,9 +742,9 @@ int rx_rach_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	l1sap.u.rach_ind.ra = ra;
 #ifdef TA_TEST
 #warning TIMING ADVANCE TEST-HACK IS ENABLED!!!
-	toa *= 10;
+	toa256 *= 10;
 #endif
-	l1sap.u.rach_ind.acc_delay = (toa >= 0) ? toa : 0;
+	l1sap.u.rach_ind.acc_delay = (toa256 >= 0) ? toa256/256 : 0;
 	l1sap.u.rach_ind.fn = fn;
 
 	/* 11bit RACH is not supported for osmo-trx */
@@ -752,7 +752,7 @@ int rx_rach_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	l1sap.u.rach_ind.burst_type = GSM_L1_BURST_TYPE_ACCESS_0;
 	l1sap.u.rach_ind.rssi = rssi;
 	l1sap.u.rach_ind.ber10k = compute_ber10k(n_bits_total, n_errors);
-	l1sap.u.rach_ind.acc_delay_256bits = 256*toa;
+	l1sap.u.rach_ind.acc_delay_256bits = toa256;
 
 	/* forward primitive */
 	l1sap_up(l1t->trx, &l1sap);
@@ -763,7 +763,7 @@ int rx_rach_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 /*! \brief a single (SDCCH/SACCH) burst was received by the PHY, process it */
 int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	struct l1sched_ts *l1ts = l1sched_trx_get_ts(l1t, tn);
 	struct l1sched_chan_state *chan_state = &l1ts->chan_state[chan];
@@ -772,7 +772,7 @@ int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	uint8_t *mask = &chan_state->ul_mask;
 	float *rssi_sum = &chan_state->rssi_sum;
 	uint8_t *rssi_num = &chan_state->rssi_num;
-	float *toa_sum = &chan_state->toa_sum;
+	int32_t *toa256_sum = &chan_state->toa256_sum;
 	uint8_t *toa_num = &chan_state->toa_num;
 	uint8_t l2[GSM_MACBLOCK_LEN], l2_len;
 	int n_errors, n_bits_total;
@@ -781,7 +781,7 @@ int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 
 	/* handle RACH, if handover RACH detection is turned on */
 	if (chan_state->ho_rach_detect == 1)
-		return rx_rach_fn(l1t, tn, fn, chan, bid, bits, GSM_BURST_LEN, rssi, toa);
+		return rx_rach_fn(l1t, tn, fn, chan, bid, bits, GSM_BURST_LEN, rssi, toa256);
 
 	LOGL1S(DL1P, LOGL_DEBUG, l1t, tn, chan, fn, "Received Data, bid=%u\n", bid);
 
@@ -799,7 +799,7 @@ int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 		*first_fn = fn;
 		*rssi_sum = 0;
 		*rssi_num = 0;
-		*toa_sum = 0;
+		*toa256_sum = 0;
 		*toa_num = 0;
 	}
 
@@ -807,7 +807,7 @@ int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	*mask |= (1 << bid);
 	*rssi_sum += rssi;
 	(*rssi_num)++;
-	*toa_sum += toa;
+	*toa256_sum += toa256;
 	(*toa_num)++;
 
 	/* copy burst to buffer of 4 bursts */
@@ -818,7 +818,7 @@ int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	/* send burst information to loops process */
 	if (L1SAP_IS_LINK_SACCH(trx_chan_desc[chan].link_id)) {
 		trx_loop_sacch_input(l1t, trx_chan_desc[chan].chan_nr | tn,
-			chan_state, rssi, toa);
+			chan_state, rssi, toa256);
 	}
 
 	/* wait until complete set of bursts */
@@ -849,18 +849,18 @@ int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 
 	/* Send uplink measurement information to L2 */
 	l1if_process_meas_res(l1t->trx, tn, *first_fn, trx_chan_desc[chan].chan_nr | tn,
-		n_errors, n_bits_total, *rssi_sum / *rssi_num, *toa_sum / *toa_num);
+		n_errors, n_bits_total, *rssi_sum / *rssi_num, *toa256_sum / *toa_num);
 	ber10k = compute_ber10k(n_bits_total, n_errors);
 	return _sched_compose_ph_data_ind(l1t, tn, *first_fn, chan, l2, l2_len,
 					  *rssi_sum / *rssi_num,
-					  4 * (*toa_sum) / *toa_num, 0, ber10k,
+					  4 * (*toa256_sum) / *toa_num, 0, ber10k,
 					  PRES_INFO_UNKNOWN);
 }
 
 /*! \brief a single PDTCH burst was received by the PHY, process it */
 int rx_pdtch_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	struct l1sched_ts *l1ts = l1sched_trx_get_ts(l1t, tn);
 	struct l1sched_chan_state *chan_state = &l1ts->chan_state[chan];
@@ -869,7 +869,7 @@ int rx_pdtch_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	uint8_t *mask = &chan_state->ul_mask;
 	float *rssi_sum = &chan_state->rssi_sum;
 	uint8_t *rssi_num = &chan_state->rssi_num;
-	float *toa_sum = &chan_state->toa_sum;
+	int32_t *toa256_sum = &chan_state->toa256_sum;
 	uint8_t *toa_num = &chan_state->toa_num;
 	uint8_t l2[EGPRS_0503_MAX_BYTES];
 	int n_errors, n_bursts_bits, n_bits_total;
@@ -893,7 +893,7 @@ int rx_pdtch_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 		*first_fn = fn;
 		*rssi_sum = 0;
 		*rssi_num = 0;
-		*toa_sum = 0;
+		*toa256_sum = 0;
 		*toa_num = 0;
 	}
 
@@ -901,7 +901,7 @@ int rx_pdtch_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	*mask |= (1 << bid);
 	*rssi_sum += rssi;
 	(*rssi_num)++;
-	*toa_sum += toa;
+	*toa256_sum += toa256;
 	(*toa_num)++;
 
 	/* copy burst to buffer of 4 bursts */
@@ -945,7 +945,7 @@ int rx_pdtch_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 
 	/* Send uplink measurement information to L2 */
 	l1if_process_meas_res(l1t->trx, tn, *first_fn, trx_chan_desc[chan].chan_nr | tn,
-		n_errors, n_bits_total, *rssi_sum / *rssi_num, *toa_sum / *toa_num);
+		n_errors, n_bits_total, *rssi_sum / *rssi_num, *toa256_sum / *toa_num);
 
 	if (rc <= 0) {
 		LOGL1S(DL1P, LOGL_DEBUG, l1t, tn, chan, fn, "Received bad PDTCH (%u/%u)\n",
@@ -954,14 +954,14 @@ int rx_pdtch_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	}
 	ber10k = compute_ber10k(n_bits_total, n_errors);
 	return _sched_compose_ph_data_ind(l1t, tn, (fn + GSM_HYPERFRAME - 3) % GSM_HYPERFRAME, chan,
-		l2, rc, *rssi_sum / *rssi_num, 4 * (*toa_sum) / *toa_num, 0,
+		l2, rc, *rssi_sum / *rssi_num, 4 * (*toa256_sum) / *toa_num, 0,
 					  ber10k, PRES_INFO_BOTH);
 }
 
 /*! \brief a single TCH/F burst was received by the PHY, process it */
 int rx_tchf_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	struct l1sched_ts *l1ts = l1sched_trx_get_ts(l1t, tn);
 	struct l1sched_chan_state *chan_state = &l1ts->chan_state[chan];
@@ -978,7 +978,7 @@ int rx_tchf_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 
 	/* handle rach, if handover rach detection is turned on */
 	if (chan_state->ho_rach_detect == 1)
-		return rx_rach_fn(l1t, tn, fn, chan, bid, bits, GSM_BURST_LEN, rssi, toa);
+		return rx_rach_fn(l1t, tn, fn, chan, bid, bits, GSM_BURST_LEN, rssi, toa256);
 
 	LOGL1S(DL1P, LOGL_DEBUG, l1t, tn, chan, fn, "Received TCH/F, bid=%u\n", bid);
 
@@ -1057,7 +1057,7 @@ int rx_tchf_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 
 	/* Send uplink measurement information to L2 */
 	l1if_process_meas_res(l1t->trx, tn, *first_fn, trx_chan_desc[chan].chan_nr|tn,
-		n_errors, n_bits_total, rssi, toa);
+		n_errors, n_bits_total, rssi, toa256);
 
 	/* Check if the frame is bad */
 	if (rc < 0) {
@@ -1075,7 +1075,7 @@ int rx_tchf_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	if (rc == GSM_MACBLOCK_LEN) {
 		uint16_t ber10k = compute_ber10k(n_bits_total, n_errors);
 		_sched_compose_ph_data_ind(l1t, tn, (fn + GSM_HYPERFRAME - 7) % GSM_HYPERFRAME, chan,
-			tch_data + amr, GSM_MACBLOCK_LEN, rssi, 4 * toa, 0,
+			tch_data + amr, GSM_MACBLOCK_LEN, rssi, 4 * toa256, 0,
 					   ber10k, PRES_INFO_UNKNOWN);
 bfi:
 		if (rsl_cmode == RSL_CMOD_SPD_SPEECH) {
@@ -1121,7 +1121,7 @@ bfi:
 /*! \brief a single TCH/H burst was received by the PHY, process it */
 int rx_tchh_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	struct l1sched_ts *l1ts = l1sched_trx_get_ts(l1t, tn);
 	struct l1sched_chan_state *chan_state = &l1ts->chan_state[chan];
@@ -1143,7 +1143,7 @@ int rx_tchh_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 
 	/* handle RACH, if handover RACH detection is turned on */
 	if (chan_state->ho_rach_detect == 1)
-		return rx_rach_fn(l1t, tn, fn, chan, bid, bits, GSM_BURST_LEN, rssi, toa);
+		return rx_rach_fn(l1t, tn, fn, chan, bid, bits, GSM_BURST_LEN, rssi, toa256);
 
 	LOGL1S(DL1P, LOGL_DEBUG, l1t, tn, chan, fn, "Received TCH/H, bid=%u\n", bid);
 
@@ -1233,7 +1233,7 @@ int rx_tchh_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 
 	/* Send uplink measurement information to L2 */
 	l1if_process_meas_res(l1t->trx, tn, *first_fn, trx_chan_desc[chan].chan_nr|tn,
-		n_errors, n_bits_total, rssi, toa);
+		n_errors, n_bits_total, rssi, toa256);
 
 	/* Check if the frame is bad */
 	if (rc < 0) {
@@ -1253,7 +1253,7 @@ int rx_tchh_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 		uint16_t ber10k = compute_ber10k(n_bits_total, n_errors);
 		_sched_compose_ph_data_ind(l1t, tn,
 			(fn + GSM_HYPERFRAME - 10 - ((fn % 26) >= 19)) % GSM_HYPERFRAME, chan,
-			tch_data + amr, GSM_MACBLOCK_LEN, rssi, 4 * toa, 0,
+			tch_data + amr, GSM_MACBLOCK_LEN, rssi, toa256/64, 0,
 					   ber10k, PRES_INFO_UNKNOWN);
 bfi:
 		if (rsl_cmode == RSL_CMOD_SPD_SPEECH) {
diff --git a/src/osmo-bts-trx/trx_if.c b/src/osmo-bts-trx/trx_if.c
index 35698ef5..f3de2453 100644
--- a/src/osmo-bts-trx/trx_if.c
+++ b/src/osmo-bts-trx/trx_if.c
@@ -520,7 +520,7 @@ static int trx_data_read_cb(struct osmo_fd *ofd, unsigned int what)
 	int len;
 	uint8_t tn;
 	int8_t rssi;
-	float toa = 0.0;
+	int16_t toa256 = 0;
 	uint32_t fn;
 	sbit_t bits[EGPRS_BURST_LEN];
 	int i, burst_len = GSM_BURST_LEN;
@@ -539,7 +539,7 @@ static int trx_data_read_cb(struct osmo_fd *ofd, unsigned int what)
 	tn = buf[0];
 	fn = (buf[1] << 24) | (buf[2] << 16) | (buf[3] << 8) | buf[4];
 	rssi = -(int8_t)buf[5];
-	toa = ((int16_t)(buf[6] << 8) | buf[7]) / 256.0F;
+	toa256 = ((int16_t)(buf[6] << 8) | buf[7]);
 
 	/* copy and convert bits {254..0} to sbits {-127..127} */
 	for (i = 0; i < burst_len; i++) {
@@ -558,20 +558,20 @@ static int trx_data_read_cb(struct osmo_fd *ofd, unsigned int what)
 		return -EINVAL;
 	}
 
-	LOGP(DTRX, LOGL_DEBUG, "RX burst tn=%u fn=%u rssi=%d toa=%.2f\n",
-		tn, fn, rssi, toa);
+	LOGP(DTRX, LOGL_DEBUG, "RX burst tn=%u fn=%u rssi=%d toa256=%d\n",
+		tn, fn, rssi, toa256);
 
 #ifdef TOA_RSSI_DEBUG
 	char deb[128];
 
 	sprintf(deb, "|                                0              "
-		"                 | rssi=%4d  toa=%4.2f fn=%u", rssi, toa, fn);
+		"                 | rssi=%4d  toa=%5d fn=%u", rssi, toa256, fn);
 	deb[1 + (128 + rssi) / 4] = '*';
 	fprintf(stderr, "%s\n", deb);
 #endif
 
 	/* feed received burst into scheduler code */
-	trx_sched_ul_burst(&l1h->l1s, tn, fn, bits, burst_len, rssi, toa);
+	trx_sched_ul_burst(&l1h->l1s, tn, fn, bits, burst_len, rssi, toa256);
 
 	return 0;
 }
diff --git a/src/osmo-bts-virtual/scheduler_virtbts.c b/src/osmo-bts-virtual/scheduler_virtbts.c
index 2283be1f..5782c0a5 100644
--- a/src/osmo-bts-virtual/scheduler_virtbts.c
+++ b/src/osmo-bts-virtual/scheduler_virtbts.c
@@ -480,7 +480,7 @@ send_burst:
 
 int rx_rach_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	return 0;
 }
@@ -488,28 +488,28 @@ int rx_rach_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 /*! \brief a single burst was received by the PHY, process it */
 int rx_data_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	return 0;
 }
 
 int rx_pdtch_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	return 0;
 }
 
 int rx_tchf_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	return 0;
 }
 
 int rx_tchh_fn(struct l1sched_trx *l1t, uint8_t tn, uint32_t fn,
 	enum trx_chan_type chan, uint8_t bid, sbit_t *bits, uint16_t nbits,
-	int8_t rssi, float toa)
+	int8_t rssi, int16_t toa256)
 {
 	return 0;
 }
-- 
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