Added PPM frame length feedback in IO comms and status command - allows to warn users about badly formatted PPM frames

src/drivers/px4io/px4io.cpp

@@ -1724,6 +1724,16 @@ PX4IO::print_status()
 		printf(" %u", io_reg_get(PX4IO_PAGE_RAW_RC_INPUT, PX4IO_P_RAW_RC_BASE + i));
 
 	printf("\n");
+
+	if (raw_inputs > 0) {
+		int frame_len = io_reg_get(PX4IO_PAGE_STATUS, PX4IO_P_STATUS_RC_DATA);
+		printf("RC data (PPM frame len) %u us\n", frame_len);
+
+		if ((frame_len - raw_inputs * 2000 - 3000) < 0) {
+			printf("WARNING  WARNING  WARNING! This RC receiver does not allow safe frame detection.\n");
+		}
+	}
+
 	uint16_t mapped_inputs = io_reg_get(PX4IO_PAGE_RC_INPUT, PX4IO_P_RC_VALID);
 	printf("mapped R/C inputs 0x%04x", mapped_inputs);
 

src/modules/px4iofirmware/controls.c

@@ -50,7 +50,7 @@
 #define RC_CHANNEL_HIGH_THRESH		5000
 #define RC_CHANNEL_LOW_THRESH		-5000
 
-static bool	ppm_input(uint16_t *values, uint16_t *num_values);
+static bool	ppm_input(uint16_t *values, uint16_t *num_values, uint16_t *frame_len);
 
 static perf_counter_t c_gather_dsm;
 static perf_counter_t c_gather_sbus;
@@ -125,7 +125,7 @@ controls_tick() {
 	 * disable the PPM decoder completely if we have S.bus signal.
 	 */
 	perf_begin(c_gather_ppm);
-	bool ppm_updated = ppm_input(r_raw_rc_values, &r_raw_rc_count);
+	bool ppm_updated = ppm_input(r_raw_rc_values, &r_raw_rc_count, &r_page_status[PX4IO_P_STATUS_RC_DATA]);
 	if (ppm_updated) {
 
 		/* XXX sample RSSI properly here */
@@ -319,7 +319,7 @@ controls_tick() {
 }
 
 static bool
-ppm_input(uint16_t *values, uint16_t *num_values)
+ppm_input(uint16_t *values, uint16_t *num_values, uint16_t *frame_len)
 {
 	bool result = false;
 
@@ -343,6 +343,10 @@ ppm_input(uint16_t *values, uint16_t *num_values)
 		/* clear validity */
 		ppm_last_valid_decode = 0;
 
+		/* store PPM frame length */
+		if (num_values)
+			*frame_len = ppm_frame_length;
+
 		/* good if we got any channels */
 		result = (*num_values > 0);
 	}

src/modules/px4iofirmware/protocol.h

@@ -124,7 +124,8 @@
 #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 */
+#define PX4IO_P_STATUS_NRSSI			9	/* [2] Normalized RSSI value, 0: no reception, 255: perfect reception */
+#define PX4IO_P_STATUS_RC_DATA			10	/* [1] + [2] Details about the RC source (PPM frame length, Spektrum protocol type) */
 
 /* array of post-mix actuator outputs, -10000..10000 */
 #define PX4IO_PAGE_ACTUATORS		2		/* 0..CONFIG_ACTUATOR_COUNT-1 */

src/modules/px4iofirmware/registers.c

@@ -89,7 +89,9 @@ uint16_t		r_page_status[] = {
 	[PX4IO_P_STATUS_IBATT]			= 0,
 	[PX4IO_P_STATUS_VSERVO]			= 0,
 	[PX4IO_P_STATUS_VRSSI]			= 0,
-	[PX4IO_P_STATUS_PRSSI]			= 0
+	[PX4IO_P_STATUS_PRSSI]			= 0,
+	[PX4IO_P_STATUS_NRSSI]			= 0,
+	[PX4IO_P_STATUS_RC_DATA]		= 0
 };
 
 /**
@@ -114,7 +116,7 @@ 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 + 24)] = 0 // XXX ensure we have enough space to decode beefy RX, will be replaced by patch soon
+	[PX4IO_P_RAW_RC_BASE ... (PX4IO_P_RAW_RC_BASE + PX4IO_CONTROL_CHANNELS)] = 0 // XXX ensure we have enough space to decode beefy RX, will be replaced by patch soon
 };
 
 /**