First stab at implementing better RSSI based connection status estimation, still needs some work and testing

src/drivers/drv_rc_input.h

@@ -89,6 +89,9 @@ struct rc_input_values {
 	/** number of channels actually being seen */
 	uint32_t		channel_count;
 
+	/** receive signal strength indicator (RSSI): < 0: Undefined, 0: no signal, 1000: full reception */
+	int32_t			rssi;
+
 	/** Input source */
 	enum RC_INPUT_SOURCE 	input_source;
 

src/modules/px4iofirmware/controls.c

@@ -94,6 +94,9 @@ controls_tick() {
 	 * other.  Don't do that.
 	 */
 
+	/* receive signal strenght indicator (RSSI). 0 = no connection, 1000: perfect connection */
+	uint16_t rssi = 0;
+
 	perf_begin(c_gather_dsm);
 	uint16_t temp_count = r_raw_rc_count;
 	bool dsm_updated = dsm_input(r_raw_rc_values, &temp_count);
@@ -104,14 +107,15 @@ controls_tick() {
 			r_status_flags |= PX4IO_P_STATUS_FLAGS_RC_DSM11;
 		else
 			r_status_flags &= ~PX4IO_P_STATUS_FLAGS_RC_DSM11;
+
+		rssi = 1000;
 	}
 	perf_end(c_gather_dsm);
 
 	perf_begin(c_gather_sbus);
-	bool sbus_updated = sbus_input(r_raw_rc_values, &r_raw_rc_count, PX4IO_CONTROL_CHANNELS /* XXX this should be INPUT channels, once untangled */);
+	bool sbus_updated = sbus_input(r_raw_rc_values, &r_raw_rc_count, &rssi, PX4IO_CONTROL_CHANNELS /* XXX this should be INPUT channels, once untangled */);
 	if (sbus_updated) {
 		r_status_flags |= PX4IO_P_STATUS_FLAGS_RC_SBUS;
-		r_raw_rc_count = 8;
 	}
 	perf_end(c_gather_sbus);
 
@@ -122,10 +126,19 @@ controls_tick() {
 	 */
 	perf_begin(c_gather_ppm);
 	bool ppm_updated = ppm_input(r_raw_rc_values, &r_raw_rc_count);
-	if (ppm_updated)
+	if (ppm_updated) {
+
+		/* XXX sample RSSI properly here */
+		rssi = 1000;
+
 		r_status_flags |= PX4IO_P_STATUS_FLAGS_RC_PPM;
+	}
 	perf_end(c_gather_ppm);
 
+	/* limit number of channels to allowable data size */
+	if (r_raw_rc_count > PX4IO_INPUT_CHANNELS)
+		r_raw_rc_count = PX4IO_INPUT_CHANNELS;
+
 	/*
 	 * In some cases we may have received a frame, but input has still
 	 * been lost.
@@ -221,7 +234,7 @@ controls_tick() {
 		 * This might happen if a protocol-based receiver returns an update
 		 * that contains no channels that we have mapped.
 		 */
-		if (assigned_channels == 0) {
+		if (assigned_channels == 0 || rssi == 0) {
 			rc_input_lost = true;
 		} else {
 			/* set RC OK flag */

src/modules/px4iofirmware/protocol.h

@@ -124,6 +124,7 @@
 #define PX4IO_P_STATUS_VSERVO			6	/* [2] servo rail voltage in mV */
 #define PX4IO_P_STATUS_VRSSI			7	/* [2] RSSI voltage */
 #define PX4IO_P_STATUS_PRSSI			8	/* [2] RSSI PWM value */
+#define PX4IO_P_STATUS_NRSSI			9	/* [2] Normalized RSSI value, 0: no reception, 1000: perfect reception */
 
 /* array of post-mix actuator outputs, -10000..10000 */
 #define PX4IO_PAGE_ACTUATORS		2		/* 0..CONFIG_ACTUATOR_COUNT-1 */

src/modules/px4iofirmware/px4io.h

@@ -209,7 +209,7 @@ extern int	dsm_init(const char *device);
 extern bool	dsm_input(uint16_t *values, uint16_t *num_values);
 extern void	dsm_bind(uint16_t cmd, int pulses);
 extern int	sbus_init(const char *device);
-extern bool	sbus_input(uint16_t *values, uint16_t *num_values, uint16_t max_channels);
+extern bool	sbus_input(uint16_t *values, uint16_t *num_values, uint16_t *rssi, uint16_t max_channels);
 
 /** global debug level for isr_debug() */
 extern volatile uint8_t debug_level;

src/modules/px4iofirmware/registers.c

@@ -114,7 +114,7 @@ uint16_t		r_page_servos[PX4IO_SERVO_COUNT];
 uint16_t		r_page_raw_rc_input[] =
 {
 	[PX4IO_P_RAW_RC_COUNT]			= 0,
-	[PX4IO_P_RAW_RC_BASE ... (PX4IO_P_RAW_RC_BASE + PX4IO_CONTROL_CHANNELS)] = 0
+	[PX4IO_P_RAW_RC_BASE ... (PX4IO_P_RAW_RC_BASE + 24)] = 0 // XXX ensure we have enough space to decode beefy RX, will be replaced by patch soon
 };
 
 /**

src/modules/px4iofirmware/sbus.c

@@ -87,7 +87,7 @@ static unsigned partial_frame_count;
 
 unsigned sbus_frame_drops;
 
-static bool sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values, uint16_t max_channels);
+static bool sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values, uint16_t *rssi, uint16_t max_channels);
 
 int
 sbus_init(const char *device)
@@ -118,7 +118,7 @@ sbus_init(const char *device)
 }
 
 bool
-sbus_input(uint16_t *values, uint16_t *num_values, uint16_t max_channels)
+sbus_input(uint16_t *values, uint16_t *num_values, uint16_t *rssi, uint16_t max_channels)
 {
 	ssize_t		ret;
 	hrt_abstime	now;
@@ -175,7 +175,7 @@ sbus_input(uint16_t *values, uint16_t *num_values, uint16_t max_channels)
 	 * decode it.
 	 */
 	partial_frame_count = 0;
-	return sbus_decode(now, values, num_values, max_channels);
+	return sbus_decode(now, values, num_values, rssi, max_channels);
 }
 
 /*
@@ -215,7 +215,7 @@ static const struct sbus_bit_pick sbus_decoder[SBUS_INPUT_CHANNELS][3] = {
 };
 
 static bool
-sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values, uint16_t max_values)
+sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values, uint16_t *rssi, uint16_t max_values)
 {
 	/* check frame boundary markers to avoid out-of-sync cases */
 	if ((frame[0] != 0x0f) || (frame[24] != 0x00)) {
@@ -266,8 +266,9 @@ sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values, uint
 
 	/* decode and handle failsafe and frame-lost flags */
 	if (frame[SBUS_FLAGS_BYTE] & (1 << SBUS_FAILSAFE_BIT)) { /* failsafe */
-		/* emulate throttle failsafe for maximum compatibility and do not destroy any channel data */
+		/* report that we failed to read anything valid off the receiver */
-		values[2] = 900;
+		*rssi = 0;
+		return false;
 	}
 	else if (frame[SBUS_FLAGS_BYTE] & (1 << SBUS_FRAMELOST_BIT)) { /* a frame was lost */
 		/* set a special warning flag or try to calculate some kind of RSSI information - to be implemented 
@@ -276,8 +277,10 @@ sbus_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values, uint
 		 * condition as fail-safe greatly reduces the reliability and range of the radio link, 
 		 * e.g. by prematurely issueing return-to-launch!!! */
 
-		// values[2] = 888; // marker for debug purposes
+		*rssi = 100; // XXX magic number indicating bad signal, but not a signal loss (yet)
 	}
 
+	*rssi = 1000;
+
 	return true;
 }