Tell L1CTL_FBSB_REQ the expected received signal level

As Dieter points out, this drastically improves the resiliance to high
receive levels on the C155.  We cannot blindly assume a received signal
level of -85 dBm if the BTS is 2m away and we actually receive -40 dBm.

This patch extends the L1CTL_FBSB_REQ data structure in layer 1 with the
respective field, as well as the l1ctl_tx_fbsb_req() API function called
from the various layer23 apps.

"mobile" and "bcch_scan" already did a PM request and thus know the
expected signal power.  "ccch_scan" and "cbch_sniff" apparently don't
do, so the -85 dBm constant is now hardcoded into the host-side source
code there, and should probably be fixed in a follow-up patch.

include/l1ctl_proto.h

@@ -167,6 +167,7 @@ struct l1ctl_fbsb_req {
 	uint8_t flags;		/* L1CTL_FBSB_F_* */
 	uint8_t sync_info_idx;
 	uint8_t ccch_mode;	/* enum ccch_mode */
+	uint8_t rxlev_exp;	/* expected signal level */
 } __attribute__((packed));
 
 #define L1CTL_FBSB_F_FB0	(1 << 0)

src/host/layer23/include/osmocom/bb/common/l1ctl.h

@@ -42,7 +42,7 @@ int l1ctl_tx_dm_rel_req(struct osmocom_ms *ms);
 /* Transmit FBSB_REQ */
 int l1ctl_tx_fbsb_req(struct osmocom_ms *ms, uint16_t arfcn,
 		      uint8_t flags, uint16_t timeout, uint8_t sync_info_idx,
-		      uint8_t ccch_mode);
+		      uint8_t ccch_mode, uint8_t rxlev_exp);
 
 /* Transmit CCCH_MODE_REQ */
 int l1ctl_tx_ccch_mode_req(struct osmocom_ms *ms, uint8_t ccch_mode);

src/host/layer23/src/common/l1ctl.c

@@ -328,7 +328,7 @@ int l1ctl_tx_data_req(struct osmocom_ms *ms, struct msgb *msg,
 /* Transmit FBSB_REQ */
 int l1ctl_tx_fbsb_req(struct osmocom_ms *ms, uint16_t arfcn,
 		      uint8_t flags, uint16_t timeout, uint8_t sync_info_idx,
-		      uint8_t ccch_mode)
+		      uint8_t ccch_mode, uint8_t rxlev_exp)
 {
 	struct msgb *msg;
 	struct l1ctl_fbsb_req *req;
@@ -351,6 +351,7 @@ int l1ctl_tx_fbsb_req(struct osmocom_ms *ms, uint16_t arfcn,
 	req->flags = flags;
 	req->sync_info_idx = sync_info_idx;
 	req->ccch_mode = ccch_mode;
+	req->rxlev_exp = rxlev_exp;
 
 	return osmo_send_l1(ms, msg);
 }

src/host/layer23/src/misc/app_cbch_sniff.c

@@ -169,7 +169,8 @@ static int signal_cb(unsigned int subsys, unsigned int signal,
 	case S_L1CTL_FBSB_ERR:
 		ms = g_ms;
 		return l1ctl_tx_fbsb_req(ms, ms->test_arfcn,
-			L1CTL_FBSB_F_FB01SB, 100, 0, CCCH_MODE_COMBINED);
+			L1CTL_FBSB_F_FB01SB, 100, 0, CCCH_MODE_COMBINED,
+			dbm2rxlev(-85));
 	case S_L1CTL_FBSB_RESP:
 		return 0;
 	}

src/host/layer23/src/misc/app_ccch_scan.c

@@ -484,7 +484,7 @@ static int signal_cb(unsigned int subsys, unsigned int signal,
 		layer3_app_reset();
 		return l1ctl_tx_fbsb_req(ms, ms->test_arfcn,
 		                         L1CTL_FBSB_F_FB01SB, 100, 0,
-		                         CCCH_MODE_NONE);
+		                         CCCH_MODE_NONE, dbm2rxlev(-85));
 		break;
 	}
 	return 0;

src/host/layer23/src/misc/bcch_scan.c

@@ -153,7 +153,8 @@ static int _cinfo_start_arfcn(unsigned int band_arfcn)
 	/* ask L1 to try to tune to new ARFCN */
 	/* FIXME: decode band */
 	rc = l1ctl_tx_fbsb_req(fps.ms, band_arfcn,
-	                       L1CTL_FBSB_F_FB01SB, 100, 0, CCCH_MODE_COMBINED);
+	                       L1CTL_FBSB_F_FB01SB, 100, 0, CCCH_MODE_COMBINED,
+			       fps.arfcn_state[band_arfcn].rxlev);
 	if (rc < 0)
 		return rc;
 

src/host/layer23/src/misc/cell_log.c

@@ -343,7 +343,7 @@ static void start_sync(void)
 	state = SCAN_STATE_SYNC;
 	l1ctl_tx_reset_req(ms, L1CTL_RES_T_FULL);
 	l1ctl_tx_fbsb_req(ms, arfcn, L1CTL_FBSB_F_FB01SB, 100, 0,
-		CCCH_MODE_NONE);
+		CCCH_MODE_NONE, pm[arfcn].rxlev);
 }
 
 static void start_pm(void)

src/host/layer23/src/mobile/gsm322.c

@@ -491,7 +491,8 @@ static int gsm322_sync_to_cell(struct gsm322_cellsel *cs,
 	l1ctl_tx_reset_req(ms, L1CTL_RES_T_FULL);
 	return l1ctl_tx_fbsb_req(ms, cs->arfcn,
 			L1CTL_FBSB_F_FB01SB, 100, 0,
-			cs->ccch_mode);
+			cs->ccch_mode,
+			cs->list[cs->arfci].rxlev);
 }
 
 /* this is called whenever the serving cell is unselectied */

src/target/firmware/layer1/prim_fbsb.c

@@ -375,7 +375,7 @@ static int l1s_fbdet_cmd(__unused uint8_t p1, __unused uint8_t p2,
 	l1s.fb.mode = fb_mode;
 
 	/* Tell the RF frontend to set the gain appropriately */
-	rffe_compute_gain(-85, CAL_DSP_TGT_BB_LVL);
+	rffe_compute_gain(rxlev2dbm(fbs.req.rxlev_exp), CAL_DSP_TGT_BB_LVL);
 
 	/* Program DSP */
 	dsp_api.db_w->d_task_md = FB_DSP_TASK;	/* maybe with I/Q swap? */
@@ -548,6 +548,7 @@ void l1s_fbsb_req(uint8_t base_fn, struct l1ctl_fbsb_req *req)
 	fbs.req.num_freqerr_avg = req->num_freqerr_avg;
 	fbs.req.flags = req->flags;
 	fbs.req.sync_info_idx = req->sync_info_idx;
+	fbs.req.rxlev_exp = req->rxlev_exp;
 
 	/* clear initial frequency error */
 	fbs.initial_freq_err = 0;