Another take on Spektrum/DSM frame decoding, based on more careful examination of the relevant docs.

7 files changed, 372 insertions, 208 deletions

diff --git a/apps/px4io/comms.c b/apps/px4io/comms.c
index 1edff25b1..3964d7503 100644
--- a/apps/px4io/comms.c
+++ b/apps/px4io/comms.c
@@ -44,6 +44,7 @@
 #include <debug.h>
 #include <stdlib.h>
 #include <errno.h>
+#include <termios.h>
 #include <string.h>
 #include <poll.h>
 
@@ -60,26 +61,126 @@
 
 static int			fmu_fd;
 static hx_stream_t		stream;
-
+static int			rx_fd;
 static struct px4io_report	report;
 
 static void			comms_handle_frame(void *arg, const void *buffer, size_t length);
 
+static struct pollfd pollfds[2];
+static int pollcount;
+
 void
 comms_init(void)
 {
+	/* initialise the FMU interface */
 	fmu_fd = open("/dev/ttyS1", O_RDWR | O_NONBLOCK);
 	if (fmu_fd < 0)
 		lib_lowprintf("COMMS: fmu open failed %d\n", errno);
-
 	stream = hx_stream_init(fmu_fd, comms_handle_frame, NULL);
+	pollfds[0].fd = fmu_fd;
+	pollfds[0].events = POLLIN;
+	pollcount = 1;
 
+	/* default state in the report to FMU */
 	report.i2f_magic = I2F_MAGIC;
+
+}
+
+static void
+serial_rx_init(unsigned serial_mode)
+{
+	if (serial_mode == system_state.serial_rx_mode)
+		return;
+	system_state.serial_rx_mode = serial_mode;
+
+	if (serial_mode == RX_MODE_PPM_ONLY) {
+		if (rx_fd != -1) {
+			pollcount = 1;
+			close(rx_fd);
+			rx_fd = -1;
+		}
+		return;
+	}
+
+	/* open the serial port used for DSM and S.bus communication */
+	rx_fd = open("/dev/ttyS0", O_RDONLY | O_NONBLOCK);
+	pollfds[1].fd = rx_fd;
+	pollfds[1].events = POLLIN;
+	pollcount = 2;
+
+	struct termios t;
+	tcgetattr(rx_fd, &t);
+
+	switch (serial_mode) {
+	case RX_MODE_DSM_10BIT:
+	case RX_MODE_DSM_11BIT:
+
+		/* 115200, no parity, one stop bit */
+		cfsetspeed(&t, 115200);
+		t.c_cflag &= ~(CSTOPB | PARENB);
+
+		dsm_init(serial_mode);
+		break;
+
+	case RX_MODE_FUTABA_SBUS:
+		/* 100000, even parity, two stop bits */
+		cfsetspeed(&t, 100000);
+		t.c_cflag |= (CSTOPB | PARENB);
+
+		sbus_init(serial_mode);
+		break;
+
+	default:
+		break;
+	}
+
+	tcsetattr(rx_fd, TCSANOW, &t);
 }
 
 void
 comms_check(void)
 {
+	/*
+	 * Check for serial data
+	 */
+	int ret = poll(pollfds, pollcount, 0);
+
+	if (ret > 0) {
+		/*
+		 * Pull bytes from FMU and feed them to the HX engine.
+		 * Limit the number of bytes we actually process on any one iteration.
+		 */
+		if (pollfds[0].revents & POLLIN) {
+			char buf[32];
+			ssize_t count = read(fmu_fd, buf, sizeof(buf));
+			for (int i = 0; i < count; i++)
+				hx_stream_rx(stream, buf[i]);
+		}
+
+		/*
+		 * Pull bytes from the serial RX port and feed them to the decoder
+		 * if we care about serial RX data.
+		 */
+		if ((pollcount > 1) && (pollfds[1].revents & POLLIN)) {
+			switch (system_state.serial_rx_mode) {
+			case RX_MODE_DSM_10BIT:
+			case RX_MODE_DSM_11BIT:
+				dsm_input(rx_fd);
+				break;
+
+			case RX_MODE_FUTABA_SBUS:
+				sbus_input(rx_fd);
+				break;
+
+			default:
+				break;
+			}
+		}
+	}
+
+	/*
+	 * Decide if it's time to send an update to the FMU.
+	 */
 	static hrt_abstime last_report_time;
 	hrt_abstime now, delta;
 
@@ -87,7 +188,7 @@ comms_check(void)
 	now = hrt_absolute_time();
 	delta = now - last_report_time;
 	if ((delta > FMU_MIN_REPORT_INTERVAL) && 
-		(system_state.fmu_report_due || (delta > FMU_MAX_REPORT_INTERVAL))) {
+	    (system_state.fmu_report_due || (delta > FMU_MAX_REPORT_INTERVAL))) {
 
 		system_state.fmu_report_due = false;
 		last_report_time = now;
@@ -101,15 +202,6 @@ comms_check(void)
 		/* and send it */
 		hx_stream_send(stream, &report, sizeof(report));
 	}
-
-	/*
-	 * Check for bytes and feed them to the RX engine.  
-	 * Limit the number of bytes we actually process on any one iteration.
-	 */
-	char buf[32];
-	ssize_t count = read(fmu_fd, buf, sizeof(buf));
-	for (int i = 0; i < count; i++)
-		hx_stream_rx(stream, buf[i]);
 }
 
 int frame_rx;
@@ -127,8 +219,7 @@ comms_handle_config(const void *buffer, size_t length)
 
 	frame_rx++;
 
-	mixer_set_serial_mode(cfg->serial_rx_mode);
-
+	serial_rx_init(cfg->serial_rx_mode);
 }
 
 static void
diff --git a/apps/px4io/dsm.c b/apps/px4io/dsm.c
new file mode 100644
index 000000000..79b6301c7
--- /dev/null
+++ b/apps/px4io/dsm.c
@@ -0,0 +1,184 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file dsm.c
+ *
+ * Serial protocol decoder for the Spektrum DSM* family of protocols.
+ *
+ * Decodes into the global PPM buffer and updates accordingly.
+ */
+
+#include <nuttx/config.h>
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+#include <systemlib/ppm_decode.h>
+ 
+#include <drivers/drv_hrt.h>
+
+#include "px4io.h"
+#include "protocol.h"
+
+#define DSM_FRAME_SIZE		16
+#define DSM_FRAME_CHANNELS	7
+
+static hrt_abstime last_frame_time;
+
+static uint8_t	frame[DSM_FRAME_SIZE];
+
+static unsigned partial_frame_count;
+static bool	insync;
+static unsigned	channel_shift;
+
+static void dsm_decode(void);
+
+void
+dsm_init(unsigned mode)
+{
+	insync = false;
+	partial_frame_count = 0;
+
+	if (mode == RX_MODE_DSM_10BIT) {
+		channel_shift = 10;
+	} else {
+		channel_shift = 11;
+	}
+
+	last_frame_time = hrt_absolute_time();
+}
+
+void
+dsm_input(int fd)
+{
+	uint8_t		buf[DSM_FRAME_SIZE];
+	ssize_t		ret;
+	hrt_abstime	now;
+
+	/*
+	 * The DSM* protocol doesn't provide any explicit framing,
+	 * so we detect frame boundaries by the inter-frame delay.
+	 *
+	 * The minimum frame spacing is 11ms; with 16 bytes at 115200bps
+	 * frame transmission time is ~1.4ms.
+	 *
+	 * We expect to only be called when bytes arrive for processing,
+	 * and if an interval of more than 5ms passes between calls, 
+	 * the first byte we read will be the first byte of a frame.
+	 */
+	now = hrt_absolute_time();
+	if ((now - last_frame_time) > 5000)
+		partial_frame_count = 0;
+
+	/*
+	 * Fetch bytes, but no more than we would need to complete
+	 * the current frame.
+	 */
+	ret = read(fd, buf, DSM_FRAME_SIZE - partial_frame_count);
+
+	/* if the read failed for any reason, just give up here */
+	if (ret < 1)
+		return;
+
+	/*
+	 * Add bytes to the current frame
+	 */
+	memcpy(&frame[partial_frame_count], buf, ret);
+	partial_frame_count += ret;
+
+	/*
+	 * If we don't have a full frame, return
+	 */
+	if (partial_frame_count < DSM_FRAME_SIZE)
+	 	return;
+	last_frame_time = now;
+
+	/*
+	 * Great, it looks like we might have a frame.  Go ahead and
+	 * decode it.
+	 */
+	dsm_decode();
+	partial_frame_count = 0;
+}
+
+static void
+dsm_decode(void)
+{
+	uint16_t	data_mask = (1 << channel_shift) - 1;
+
+	/*
+	 * The encoding of the first byte is uncertain, so we're going
+	 * to ignore it for now.
+	 *
+	 * The second byte may tell us about the protocol, but it's not
+	 * actually very interesting since what we really want to know
+	 * is how the channel data is formatted, and there doesn't seem
+	 * to be a reliable way to determine this from the protocol ID
+	 * alone.
+	 *
+	 * Each channel is a 16-bit unsigned value containing either a 10-
+	 * or 11-bit channel value and a 4-bit channel number, shifted
+	 * either 10 or 11 bits. The MSB may also be set to indicate the
+	 * second frame in variants of the protocol where more than
+	 * seven channels are being transmitted.
+	 */
+
+	for (unsigned i = 0; i < DSM_FRAME_CHANNELS; i++) {
+
+		uint8_t *dp = &frame[2 + (2 * i)];
+		uint16_t raw = (dp[0] << 8) | dp[1];
+
+		/* ignore pad channels */
+		if (raw == 0xffff)
+			continue;
+
+		unsigned channel = (raw >> channel_shift) & 0xf;
+
+		/* ignore channels out of range */
+		if (channel >= PX4IO_INPUT_CHANNELS)
+			continue;
+
+		if (channel > ppm_decoded_channels)
+			ppm_decoded_channels = channel;
+
+		/* convert 0-1024 / 0-2048 values to 1000-2000 ppm encoding in a very sloppy fashion */
+		unsigned data = raw & data_mask;
+		if (channel_shift == 11)
+			data /= 2;
+		ppm_buffer[channel] = 988 + data;
+
+	}
+	ppm_last_valid_decode = hrt_absolute_time();
+}
diff --git a/apps/px4io/mixer.c b/apps/px4io/mixer.c
index 471965fd7..b614f3fa4 100644
--- a/apps/px4io/mixer.c
+++ b/apps/px4io/mixer.c
@@ -32,7 +32,9 @@
  ****************************************************************************/
 
 /**
- * @file Control channel input/output mixer and failsafe.
+ * @file mixer.c
+ *
+ * Control channel input/output mixer and failsafe.
  */
 
 #include <nuttx/config.h>
@@ -43,8 +45,6 @@
 #include <string.h>
 #include <assert.h>
 #include <errno.h>
-#include <fcntl.h>
-#include <termios.h>
 #include <unistd.h>
 #include <fcntl.h>
 
@@ -56,23 +56,12 @@
 #include "px4io.h"
 
 /*
- * Count of periodic calls in which we have no data.
- */
-static unsigned mixer_input_drops;
-#define MIXER_INPUT_DROP_LIMIT	10
-
-/*
  * Count of periodic calls in which we have no FMU input.
  */
 static unsigned fmu_input_drops;
 #define FMU_INPUT_DROP_LIMIT	20
 
 /*
- * Serial port fd for serial RX protocols
- */
-static int rx_port = -1;
-
-/*
  * HRT periodic call used to check for control input data.
  */
 static struct hrt_call mixer_input_call;
@@ -106,8 +95,7 @@ struct mixer {
 int
 mixer_init(void)
 {
-	/* open the serial port */
-	rx_port = open("/dev/ttyS0", O_RDONLY | O_NONBLOCK);
+
 
 	/* look for control data at 50Hz */
 	hrt_call_every(&mixer_input_call, 1000, 20000, mixer_tick, NULL);
@@ -115,37 +103,6 @@ mixer_init(void)
 	return 0;
 }
 
-void
-mixer_set_serial_mode(uint8_t serial_mode)
-{
-
-	if (serial_mode == system_state.serial_rx_mode)
-		return;
-
-	struct termios t;
-	tcgetattr(rx_port, &t);
-
-	switch (serial_mode) {
-	case RX_MODE_PPM_ONLY:
-		break;
-	case RX_MODE_SPEKTRUM_6:
-	case RX_MODE_SPEKTRUM_7:
-		/* 115200, no parity, one stop bit */
-		cfsetspeed(&t, 115200);
-		t.c_cflag &= ~(CSTOPB | PARENB);
-		break;
-	case RX_MODE_FUTABA_SBUS:
-		/* 100000, even parity, two stop bits */
-		cfsetspeed(&t, 100000);
-		t.c_cflag |= (CSTOPB | PARENB);
-		break;
-	default:
-		return;
-	}
-
-	tcsetattr(rx_port, TCSANOW, &t);
-	system_state.serial_rx_mode = serial_mode;
-}
 
 static void
 mixer_tick(void *arg)
@@ -234,148 +191,20 @@ mixer_update(int mixer, uint16_t *inputs, int input_count)
 	}
 }
 
-static bool
-mixer_get_spektrum_input(void)
-{
-	static uint8_t buf[16];
-	static unsigned count;
-
-	/* always read as much data as we can into the buffer */
-	if (count >= sizeof(buf))
-		count = 0;
-	ssize_t result = read(rx_port, buf, sizeof(buf) - count);
-	/* no data or an error */
-	if (result <= 0)
-		return false;
-	count += result;
-
-	/* if there are more than two bytes in the buffer, check for sync */
-	if (count >= 2) {
-		if ((buf[0] != 0x3) || (buf[1] != 0x1)) {
-			/* not in sync; look for a possible sync marker */
-			for (unsigned i = 1; i < count; i++) {
-				if (buf[i] == 0x3) {
-					/* could be a frame marker; move buffer bytes */
-					count -= i;
-					memmove(buf, buf + i, count);
-					break;
-				}
-			}
-		}
-	}
-	if (count < sizeof(buf))
-		return false;
-
-	/* we got a frame; decode it */
-	const uint16_t *channels = (const uint16_t *)&buf[2];
-
-	/*
-	 * Channel assignment for DX6i vs. DX7 is different.
-	 *
-	 * DX7 etc. is:
-	 *
-	 * 0: Aileron
-	 * 1: Flaps
-	 * 2: Gear
-	 * 3: Elevator
-	 * 4: Aux2
-	 * 5: Throttle
-	 * 6: Rudder
-	 *
-	 * DX6i is:
-	 *
-	 * 0: Aileron	
-	 * 1: Flaps
-	 * 2: Elevator
-	 * 3: Rudder
-	 * 4: Throttle
-	 * 5: Gear
-	 * 6: <notused>
-	 *
-	 * We convert these to our standard Futaba-style assignment:
-	 *
-	 * 0: Throttle  (Throttle)
-	 * 1: Roll      (Aileron)
-	 * 2: Pitch     (Elevator)
-	 * 3: Yaw       (Rudder)
-	 * 4: Override  (Flaps)
-	 * 5: FUNC_0    (Gear)
-	 * 6: FUNC_1    (Aux2)
-	 */
-	if (system_state.serial_rx_mode == RX_MODE_SPEKTRUM_7) {
-		system_state.rc_channel_data[0] = channels[5]; /* Throttle */
-		system_state.rc_channel_data[1] = channels[0]; /* Roll */
-		system_state.rc_channel_data[2] = channels[3]; /* Pitch */
-		system_state.rc_channel_data[3] = channels[6]; /* Yaw */
-		system_state.rc_channel_data[4] = channels[1]; /* Override */
-		system_state.rc_channel_data[5] = channels[2]; /* FUNC_0 */
-		system_state.rc_channel_data[6] = channels[4]; /* FUNC_1 */
-		system_state.rc_channels = 7;
-	} else {
-		system_state.rc_channel_data[0] = channels[4]; /* Throttle */
-		system_state.rc_channel_data[1] = channels[0]; /* Roll */
-		system_state.rc_channel_data[2] = channels[2]; /* Pitch */
-		system_state.rc_channel_data[3] = channels[3]; /* Yaw */
-		system_state.rc_channel_data[4] = channels[1]; /* Override */
-		system_state.rc_channel_data[5] = channels[5]; /* FUNC_0 */
-		system_state.rc_channels = 6;
-	}
-	count = 0;
-	return true;
-}
-
-static bool
-mixer_get_sbus_input(void)
-{
-	/* XXX not implemented yet */
-	return false;
-}
-
 static void
 mixer_get_rc_input(void)
 {
-	bool got_input = false;
-
-	switch (system_state.serial_rx_mode) {
-	case RX_MODE_PPM_ONLY:
-		if (ppm_decoded_channels > 0) {
-			/* copy channel data */
-			system_state.rc_channels = ppm_decoded_channels;
-			for (unsigned i = 0; i < ppm_decoded_channels; i++)
-				system_state.rc_channel_data[i] = ppm_buffer[i];
-			got_input = true;
-		}
-		break;
-
-	case RX_MODE_SPEKTRUM_6:
-	case RX_MODE_SPEKTRUM_7:
-		got_input = mixer_get_spektrum_input();
-		break;
-
-	case RX_MODE_FUTABA_SBUS:
-		got_input = mixer_get_sbus_input();
-		break;
-
-	default:
-		break;
-	}
 
-	if (got_input) {
-		mixer_input_drops = 0;
+	/* if we haven't seen any new data in 200ms, assume we have lost input and tell FMU */
+	if ((hrt_absolute_time() - ppm_last_valid_decode) > 200000) {
+		system_state.rc_channels = 0;
 		system_state.fmu_report_due = true;
-	} else {
-		/*
-		 * No data; count the 'frame drops' and once we hit the limit
-		 * assume that we have lost input.
-		 */
-		if (mixer_input_drops < MIXER_INPUT_DROP_LIMIT) {
-			mixer_input_drops++;
-
-			/* if we hit the limit, stop pretending we have input and let the FMU know */
-			if (mixer_input_drops == MIXER_INPUT_DROP_LIMIT) {
-				system_state.rc_channels = 0;
-				system_state.fmu_report_due = true;
-			}
-		}
+		return;
 	}
+
+	/* otherwise, copy channel data */
+	system_state.rc_channels = ppm_decoded_channels;
+	for (unsigned i = 0; i < ppm_decoded_channels; i++)
+		system_state.rc_channel_data[i] = ppm_buffer[i];
+	system_state.fmu_report_due = true;
 }
diff --git a/apps/px4io/protocol.h b/apps/px4io/protocol.h
index 7467f1adc..660eed12b 100644
--- a/apps/px4io/protocol.h
+++ b/apps/px4io/protocol.h
@@ -41,11 +41,6 @@
 
 #pragma once
 
-/*
- * XXX MUST BE KEPT IN SYNC WITH THE VERSION IN PX4FMU UNTIL
- * TREES ARE MERGED.
- */
-
 #define PX4IO_OUTPUT_CHANNELS	8
 #define PX4IO_INPUT_CHANNELS	12
 #define PX4IO_RELAY_CHANNELS	4
@@ -69,8 +64,8 @@ struct px4io_config {
 
 	uint8_t		serial_rx_mode;
 #define RX_MODE_PPM_ONLY	0
-#define RX_MODE_SPEKTRUM_6	1
-#define RX_MODE_SPEKTRUM_7	2
+#define RX_MODE_DSM_10BIT	1
+#define RX_MODE_DSM_11BIT	2
 #define RX_MODE_FUTABA_SBUS	3
 };
 
diff --git a/apps/px4io/px4io.c b/apps/px4io/px4io.c
index 7039e5d58..e02d865d5 100644
--- a/apps/px4io/px4io.c
+++ b/apps/px4io/px4io.c
@@ -72,7 +72,7 @@ int user_start(int argc, char *argv[])
 	/* configure the high-resolution time/callout interface */
 	hrt_init();
 
-	/* init the FMU link */
+	/* init the FMU and receiver links */
 	comms_init();
 
 	/* configure the first 8 PWM outputs (i.e. all of them) */
diff --git a/apps/px4io/px4io.h b/apps/px4io/px4io.h
index 274b27ff3..536dbebf1 100644
--- a/apps/px4io/px4io.h
+++ b/apps/px4io/px4io.h
@@ -147,7 +147,6 @@ extern volatile int	timers[TIMER_NUM_TIMERS];
  * Mixer
  */
 extern int	mixer_init(void);
-extern void	mixer_set_serial_mode(uint8_t newmode);
 
 /*
  * Safety switch/LED.
@@ -161,6 +160,14 @@ extern void	comms_init(void);
 extern void	comms_check(void);
 
 /*
+ * Serial receiver decoders.
+ */
+extern void	dsm_init(unsigned mode);
+extern void	dsm_input(int fd);
+extern void	sbus_init(unsigned mode);
+extern void	sbus_input(int fd);
+
+/*
  * Assertion codes
  */
 #define A_GPIO_OPEN_FAIL		100
diff --git a/apps/px4io/sbus.c b/apps/px4io/sbus.c
new file mode 100644
index 000000000..e363a0a78
--- /dev/null
+++ b/apps/px4io/sbus.c
@@ -0,0 +1,58 @@
+/****************************************************************************
+ *
+ *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file sbus.c
+ *
+ * Serial protocol decoder for the Futaba S.bus protocol.
+ */
+
+#include <nuttx/config.h>
+
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <drivers/drv_hrt.h>
+
+#include "px4io.h"
+#include "protocol.h"
+
+void
+sbus_init(unsigned mode)
+{
+}
+
+void
+sbus_input(int fd)
+{
+}