Merged master

3 files changed, 329 insertions, 224 deletions

diff --git a/src/drivers/px4io/px4io.cpp b/src/drivers/px4io/px4io.cpp
index ed98ff0a5..cebe33996 100644
--- a/src/drivers/px4io/px4io.cpp
+++ b/src/drivers/px4io/px4io.cpp
@@ -92,21 +92,62 @@ extern device::Device *PX4IO_serial_interface() weak_function;
 #define PX4IO_SET_DEBUG			_IOC(0xff00, 0)
 #define PX4IO_INAIR_RESTART_ENABLE	_IOC(0xff00, 1)
 
+/**
+ * The PX4IO class.
+ *
+ * Encapsulates PX4FMU to PX4IO communications modeled as file operations.
+ */
 class PX4IO : public device::CDev
 {
 public:
+	/**
+	 * Constructor.
+	 * 
+	 * Initialize all class variables.
+	 */
 	PX4IO(device::Device *interface);
+
+	/**
+	 * Destructor.
+	 * 
+	 * Wait for worker thread to terminate.
+	 */
 	virtual ~PX4IO();
 
+	/**
+	 * Initialize the PX4IO class.
+	 * 
+	 * Initialize the physical I2C interface to PX4IO. Retrieve relevant initial system parameters. Initialize PX4IO registers.
+	 */
 	virtual int		init();
 
+	/**
+	 * IO Control handler.
+	 * 
+	 * Handle all IOCTL calls to the PX4IO file descriptor.
+	 *
+	 * @param[in] filp file handle (not used). This function is always called directly through object reference
+	 * @param[in] cmd the IOCTL command
+	 * @param[in] the IOCTL command parameter (optional)
+	 */
 	virtual int		ioctl(file *filp, int cmd, unsigned long arg);
+
+	/**
+	 * write handler.
+	 * 
+	 * Handle writes to the PX4IO file descriptor.
+	 *
+	 * @param[in] filp file handle (not used). This function is always called directly through object reference
+	 * @param[in] buffer pointer to the data buffer to be written
+	 * @param[in] len size in bytes to be written
+	 * @return number of bytes written
+	 */
 	virtual ssize_t		write(file *filp, const char *buffer, size_t len);
 
 	/**
 	* Set the update rate for actuator outputs from FMU to IO.
 	*
-	* @param rate		The rate in Hz actuator outpus are sent to IO.
+	* @param[in] rate		The rate in Hz actuator outpus are sent to IO.
 	* 			Min 10 Hz, max 400 Hz
 	*/
 	int      		set_update_rate(int rate);
@@ -114,29 +155,41 @@ public:
 	/**
 	* Set the battery current scaling and bias
 	*
-	* @param amp_per_volt
-	* @param amp_bias
+	* @param[in] amp_per_volt
+	* @param[in] amp_bias
 	*/
 	void      		set_battery_current_scaling(float amp_per_volt, float amp_bias);
 
 	/**
 	 * Push failsafe values to IO.
 	 *
-	 * @param vals		Failsafe control inputs: in us PPM (900 for zero, 1500 for centered, 2100 for full)
-	 * @param len		Number of channels, could up to 8
+	 * @param[in] vals	Failsafe control inputs: in us PPM (900 for zero, 1500 for centered, 2100 for full)
+	 * @param[in] len	Number of channels, could up to 8
 	 */
 	int			set_failsafe_values(const uint16_t *vals, unsigned len);
 
 	/**
-	 * Print the current status of IO
+	 * Print IO status.
+	 *
+	 * Print all relevant IO status information
 	 */
 	void			print_status();
 
+	/**
+	 * Set the DSM VCC is controlled by relay one flag
+	 *
+	 * @param[in] enable true=DSM satellite VCC is controlled by relay1, false=DSM satellite VCC not controlled
+	 */
 	inline void		set_dsm_vcc_ctl(bool enable)
 	{
 		_dsm_vcc_ctl = enable;
 	};
 
+	/**
+	 * Get the DSM VCC is controlled by relay one flag
+	 *
+	 * @return true=DSM satellite VCC is controlled by relay1, false=DSM satellite VCC not controlled
+	 */
 	inline bool		get_dsm_vcc_ctl()
 	{
 		return _dsm_vcc_ctl;
@@ -146,59 +199,49 @@ private:
 	device::Device		*_interface;
 
 	// XXX
-	unsigned		_hardware;
-	unsigned		_max_actuators;
-	unsigned		_max_controls;
-	unsigned		_max_rc_input;
-	unsigned		_max_relays;
-	unsigned		_max_transfer;
+	unsigned		_hardware;			///< Hardware revision
+	unsigned		_max_actuators;		///<Maximum # of actuators supported by PX4IO
+	unsigned		_max_controls;		///<Maximum # of controls supported by PX4IO
+	unsigned		_max_rc_input;		///<Maximum receiver channels supported by PX4IO
+	unsigned		_max_relays;		///<Maximum relays supported by PX4IO
+	unsigned		_max_transfer;		///<Maximum number of I2C transfers supported by PX4IO
 
-	unsigned 		_update_interval; ///< subscription interval limiting send rate
+	unsigned 		_update_interval;	///<Subscription interval limiting send rate
 
-	volatile int		_task;		///< worker task
-	volatile bool		_task_should_exit;
+	volatile int		_task;			///<worker task id
+	volatile bool		_task_should_exit;	///<worker terminate flag
 
-	int			_mavlink_fd;
+	int			_mavlink_fd;		///<mavlink file descriptor
 
-	perf_counter_t		_perf_update;
+	perf_counter_t		_perf_update;		///<local performance counter
 
 	/* cached IO state */
-	uint16_t		_status;
-	uint16_t		_alarms;
+	uint16_t		_status;		///<Various IO status flags
+	uint16_t		_alarms;		///<Various IO alarms
 
 	/* subscribed topics */
-	int			_t_actuators;	///< actuator controls topic
-	int			_t_armed;	///< system armed control topic
-	int 			_t_vstatus;	///< system / vehicle status
-	int			_t_param;	///< parameter update topic
+	int			_t_actuators;		///<actuator controls topic
+	int			_t_armed;		///<system armed control topic
+	int 			_t_vstatus;		///<system / vehicle status
+	int			_t_param;		///<parameter update topic
 
 	/* advertised topics */
-	orb_advert_t 		_to_input_rc;	///< rc inputs from io
-	orb_advert_t 		_to_actuators_effective; ///< effective actuator controls topic
-	orb_advert_t		_to_outputs;	///< mixed servo outputs topic
-	orb_advert_t		_to_battery;	///< battery status / voltage
-
-	actuator_outputs_s	_outputs;	///< mixed outputs
-	actuator_controls_effective_s _controls_effective; ///< effective controls
+	orb_advert_t 		_to_input_rc;		///<rc inputs from IO topic
+	orb_advert_t 		_to_actuators_effective; ///<effective actuator controls topic
+	orb_advert_t		_to_outputs;		///<mixed servo outputs topic
+	orb_advert_t		_to_battery;		///<battery status / voltage topic
 
-	bool			_primary_pwm_device;	///< true if we are the default PWM output
+	actuator_outputs_s	_outputs;		///<mixed outputs
+	actuator_controls_effective_s _controls_effective; ///<effective controls
 
-	float			_battery_amp_per_volt;
-	float			_battery_amp_bias;
-	float			_battery_mamphour_total;
-	uint64_t		_battery_last_timestamp;
+	bool			_primary_pwm_device;	///<true if we are the default PWM output
 
-	/**
-	 * Relay1 is dedicated to controlling DSM receiver power
-	 */
-
-	bool			_dsm_vcc_ctl;
-
-	/**
-	 * System armed
-	 */
+	float			_battery_amp_per_volt;	///<current sensor amps/volt
+	float			_battery_amp_bias;	///<current sensor bias
+	float			_battery_mamphour_total;///<amp hours consumed so far
+	uint64_t		_battery_last_timestamp;///<last amp hour calculation timestamp
 
-	bool			_system_armed;
+	bool			_dsm_vcc_ctl;		///<true if relay 1 controls DSM satellite RX power
 
 	/**
 	 * Trampoline to the worker task
@@ -369,8 +412,7 @@ PX4IO::PX4IO(device::Device *interface) :
 	_battery_amp_bias(0),
 	_battery_mamphour_total(0),
 	_battery_last_timestamp(0),
-	_dsm_vcc_ctl(false),
-	_system_armed(false)
+	_dsm_vcc_ctl(false)
 {
 	/* we need this potentially before it could be set in task_main */
 	g_dev = this;
@@ -705,7 +747,7 @@ PX4IO::task_main()
 				// See if bind parameter has been set, and reset it to 0
 				param_get(dsm_bind_param = param_find("RC_DSM_BIND"), &dsm_bind_val);
 				if (dsm_bind_val) {
-					if (!_system_armed) {
+					if (!(_status & PX4IO_P_STATUS_FLAGS_ARMED)) {
 						if ((dsm_bind_val == 1) || (dsm_bind_val == 2)) {
 							mavlink_log_info(mavlink_fd, "[IO] binding dsm%c rx", dsm_bind_val == 1 ? '2' : 'x');
 							ioctl(nullptr, DSM_BIND_START, dsm_bind_val == 1 ? 3 : 7);
@@ -784,8 +826,6 @@ PX4IO::io_set_arming_state()
 	uint16_t set = 0;
 	uint16_t clear = 0;
 
-	_system_armed = vstatus.flag_system_armed;
-
 	if (armed.armed && !armed.lockdown) {
 		set |= PX4IO_P_SETUP_ARMING_FMU_ARMED;
 	} else {
@@ -1635,7 +1675,8 @@ PX4IO::ioctl(file * /*filep*/, int cmd, unsigned long arg)
 }
 
 ssize_t
-PX4IO::write(file *filp, const char *buffer, size_t len)
+PX4IO::write(file * /*filp*/, const char *buffer, size_t len)
+/* Make it obvious that file * isn't used here */
 {
 	unsigned count = len / 2;
 
diff --git a/src/modules/px4iofirmware/dsm.c b/src/modules/px4iofirmware/dsm.c
index 4925ced54..206e27db5 100644
--- a/src/modules/px4iofirmware/dsm.c
+++ b/src/modules/px4iofirmware/dsm.c
@@ -48,161 +48,44 @@
 
 #include <drivers/drv_hrt.h>
 
-#define DEBUG
-
 #include "px4io.h"
 
-#define DSM_FRAME_SIZE		16
-#define DSM_FRAME_CHANNELS	7
-
-static int dsm_fd = -1;
-
-static hrt_abstime last_rx_time;
-static hrt_abstime last_frame_time;
-
-static uint8_t	frame[DSM_FRAME_SIZE];
-
-static unsigned partial_frame_count;
-static unsigned	channel_shift;
-
-unsigned dsm_frame_drops;
-
-static bool dsm_decode_channel(uint16_t raw, unsigned shift, unsigned *channel, unsigned *value);
-static void dsm_guess_format(bool reset);
-static bool dsm_decode(hrt_abstime now, uint16_t *values, uint16_t *num_values);
-
-int
-dsm_init(const char *device)
-{
-	if (dsm_fd < 0)
-		dsm_fd = open(device, O_RDONLY | O_NONBLOCK);
-
-	if (dsm_fd >= 0) {
-		struct termios t;
-
-		/* 115200bps, no parity, one stop bit */
-		tcgetattr(dsm_fd, &t);
-		cfsetspeed(&t, 115200);
-		t.c_cflag &= ~(CSTOPB | PARENB);
-		tcsetattr(dsm_fd, TCSANOW, &t);
-
-		/* initialise the decoder */
-		partial_frame_count = 0;
-		last_rx_time = hrt_absolute_time();
-
-		/* reset the format detector */
-		dsm_guess_format(true);
-
-		debug("DSM: ready");
-
-	} else {
-		debug("DSM: open failed");
-	}
-
-	return dsm_fd;
-}
-
-void
-dsm_bind(uint16_t cmd, int pulses)
-{
-	const uint32_t usart1RxAsOutp = GPIO_OUTPUT|GPIO_CNF_OUTPP|GPIO_MODE_50MHz|GPIO_OUTPUT_SET|GPIO_PORTA|GPIO_PIN10;
-
-	if (dsm_fd < 0)
-		return;
-
-#ifdef CONFIG_ARCH_BOARD_PX4IO_V2
-	// XXX implement
-	#warning DSM BIND NOT IMPLEMENTED ON PX4IO V2
-#else
-	switch (cmd) {
-	case dsm_bind_power_down:
-		// power down DSM satellite
-		POWER_RELAY1(0);
-		break;
-	case dsm_bind_power_up:
-		POWER_RELAY1(1);
-		dsm_guess_format(true);
-		break;
-	case dsm_bind_set_rx_out:
-		stm32_configgpio(usart1RxAsOutp); 
-		break;
-	case dsm_bind_send_pulses:
-		for (int i = 0; i < pulses; i++) {
-			stm32_gpiowrite(usart1RxAsOutp, false);
-			up_udelay(25);
-			stm32_gpiowrite(usart1RxAsOutp, true);
-			up_udelay(25);
-		}
-		break;
-	case dsm_bind_reinit_uart:
-		// Restore USART rx pin
-		stm32_configgpio(GPIO_USART1_RX);
-		break;
-	}
-#endif
-}
-
-bool
-dsm_input(uint16_t *values, uint16_t *num_values)
-{
-	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.
-	 *
-	 * In the case where byte(s) are dropped from a frame, this also
-	 * provides a degree of protection. Of course, it would be better
-	 * if we didn't drop bytes...
-	 */
-	now = hrt_absolute_time();
-
-	if ((now - last_rx_time) > 5000) {
-		if (partial_frame_count > 0) {
-			dsm_frame_drops++;
-			partial_frame_count = 0;
-		}
-	}
+#define DSM_FRAME_SIZE		16		/**<DSM frame size in bytes*/
+#define DSM_FRAME_CHANNELS	7		/**<Max supported DSM channels*/
 
-	/*
-	 * Fetch bytes, but no more than we would need to complete
-	 * the current frame.
-	 */
-	ret = read(dsm_fd, &frame[partial_frame_count], DSM_FRAME_SIZE - partial_frame_count);
-
-	/* if the read failed for any reason, just give up here */
-	if (ret < 1)
-		return false;
-
-	last_rx_time = now;
-
-	/*
-	 * Add bytes to the current frame
-	 */
-	partial_frame_count += ret;
-
-	/*
-	 * If we don't have a full frame, return
-	 */
-	if (partial_frame_count < DSM_FRAME_SIZE)
-		return false;
-
-	/*
-	 * Great, it looks like we might have a frame.  Go ahead and
-	 * decode it.
-	 */
-	partial_frame_count = 0;
-	return dsm_decode(now, values, num_values);
-}
+static int dsm_fd = -1;						/**< File handle to the DSM UART */
+static hrt_abstime dsm_last_rx_time;		/**< Timestamp when we last received */
+static hrt_abstime dsm_last_frame_time;		/**< Timestamp for start of last dsm frame */
+static uint8_t dsm_frame[DSM_FRAME_SIZE];	/**< DSM dsm frame receive buffer */
+static unsigned dsm_partial_frame_count;	/**< Count of bytes received for current dsm frame */
+static unsigned dsm_channel_shift;			/**< Channel resolution, 0=unknown, 1=10 bit, 2=11 bit */
+static unsigned dsm_frame_drops;			/**< Count of incomplete DSM frames */
 
+/**
+ * Attempt to decode a single channel raw channel datum
+ *
+ * The DSM* protocol doesn't provide any explicit framing,
+ * so we detect dsm frame boundaries by the inter-dsm frame delay.
+ *
+ * The minimum dsm frame spacing is 11ms; with 16 bytes at 115200bps
+ * dsm 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 dsm frame.
+ *
+ * In the case where byte(s) are dropped from a dsm frame, this also
+ * provides a degree of protection. Of course, it would be better
+ * if we didn't drop bytes...
+ *
+ * Upon receiving a full dsm frame we attempt to decode it
+ *
+ * @param[in] raw 16 bit raw channel value from dsm frame
+ * @param[in] shift position of channel number in raw data
+ * @param[out] channel pointer to returned channel number
+ * @param[out] value pointer to returned channel value
+ * @return true=raw value successfully decoded
+ */
 static bool
 dsm_decode_channel(uint16_t raw, unsigned shift, unsigned *channel, unsigned *value)
 {
@@ -220,6 +103,11 @@ dsm_decode_channel(uint16_t raw, unsigned shift, unsigned *channel, unsigned *va
 	return true;
 }
 
+/**
+ * Attempt to guess if receiving 10 or 11 bit channel values
+ *
+ * @param[in] reset true=reset the 10/11 bit state to unknown
+ */
 static void
 dsm_guess_format(bool reset)
 {
@@ -232,14 +120,14 @@ dsm_guess_format(bool reset)
 		cs10 = 0;
 		cs11 = 0;
 		samples = 0;
-		channel_shift = 0;
+		dsm_channel_shift = 0;
 		return;
 	}
 
-	/* scan the channels in the current frame in both 10- and 11-bit mode */
+	/* scan the channels in the current dsm_frame in both 10- and 11-bit mode */
 	for (unsigned i = 0; i < DSM_FRAME_CHANNELS; i++) {
 
-		uint8_t *dp = &frame[2 + (2 * i)];
+		uint8_t *dp = &dsm_frame[2 + (2 * i)];
 		uint16_t raw = (dp[0] << 8) | dp[1];
 		unsigned channel, value;
 
@@ -250,10 +138,10 @@ dsm_guess_format(bool reset)
 		if (dsm_decode_channel(raw, 11, &channel, &value) && (channel < 31))
 			cs11 |= (1 << channel);
 
-		/* XXX if we cared, we could look for the phase bit here to decide 1 vs. 2-frame format */
+		/* XXX if we cared, we could look for the phase bit here to decide 1 vs. 2-dsm_frame format */
 	}
 
-	/* wait until we have seen plenty of frames - 2 should normally be enough */
+	/* wait until we have seen plenty of frames - 5 should normally be enough */
 	if (samples++ < 5)
 		return;
 
@@ -289,13 +177,13 @@ dsm_guess_format(bool reset)
 	}
 
 	if ((votes11 == 1) && (votes10 == 0)) {
-		channel_shift = 11;
+		dsm_channel_shift = 11;
 		debug("DSM: 11-bit format");
 		return;
 	}
 
 	if ((votes10 == 1) && (votes11 == 0)) {
-		channel_shift = 10;
+		dsm_channel_shift = 10;
 		debug("DSM: 10-bit format");
 		return;
 	}
@@ -305,27 +193,136 @@ dsm_guess_format(bool reset)
 	dsm_guess_format(true);
 }
 
+/**
+ * Initialize the DSM receive functionality
+ *
+ * Open the UART for receiving DSM frames and configure it appropriately
+ *
+ * @param[in] device Device name of DSM UART
+ */
+int
+dsm_init(const char *device)
+{
+	if (dsm_fd < 0)
+		dsm_fd = open(device, O_RDONLY | O_NONBLOCK);
+
+	if (dsm_fd >= 0) {
+
+		struct termios t;
+
+		/* 115200bps, no parity, one stop bit */
+		tcgetattr(dsm_fd, &t);
+		cfsetspeed(&t, 115200);
+		t.c_cflag &= ~(CSTOPB | PARENB);
+		tcsetattr(dsm_fd, TCSANOW, &t);
+
+		/* initialise the decoder */
+		dsm_partial_frame_count = 0;
+		dsm_last_rx_time = hrt_absolute_time();
+
+		/* reset the format detector */
+		dsm_guess_format(true);
+
+		debug("DSM: ready");
+
+	} else {
+
+		debug("DSM: open failed");
+
+	}
+
+	return dsm_fd;
+}
+
+/**
+ * Handle DSM satellite receiver bind mode handler
+ *
+ * @param[in] cmd commands - dsm_bind_power_down, dsm_bind_power_up, dsm_bind_set_rx_out, dsm_bind_send_pulses, dsm_bind_reinit_uart
+ * @param[in] pulses Number of pulses for dsm_bind_send_pulses command
+ */
+void
+dsm_bind(uint16_t cmd, int pulses)
+{
+	const uint32_t usart1RxAsOutp =
+		GPIO_OUTPUT | GPIO_CNF_OUTPP | GPIO_MODE_50MHz | GPIO_OUTPUT_SET | GPIO_PORTA | GPIO_PIN10;
+
+	if (dsm_fd < 0)
+		return;
+
+#ifdef CONFIG_ARCH_BOARD_PX4IO_V2
+	// XXX implement
+	#warning DSM BIND NOT IMPLEMENTED ON PX4IO V2
+#else
+	switch (cmd) {
+
+	case dsm_bind_power_down:
+
+		/*power down DSM satellite*/
+		POWER_RELAY1(0);
+		break;
+
+	case dsm_bind_power_up:
+
+		/*power up DSM satellite*/
+		POWER_RELAY1(1);
+		dsm_guess_format(true);
+		break;
+
+	case dsm_bind_set_rx_out:
+
+		/*Set UART RX pin to active output mode*/
+		stm32_configgpio(usart1RxAsOutp);
+		break;
+
+	case dsm_bind_send_pulses:
+
+		/*Pulse RX pin a number of times*/
+		for (int i = 0; i < pulses; i++) {
+			stm32_gpiowrite(usart1RxAsOutp, false);
+			up_udelay(25);
+			stm32_gpiowrite(usart1RxAsOutp, true);
+			up_udelay(25);
+		}
+		break;
+
+	case dsm_bind_reinit_uart:
+
+		/*Restore USART RX pin to RS232 receive mode*/
+		stm32_configgpio(GPIO_USART1_RX);
+		break;
+
+	}
+#endif
+}
+
+/**
+ * Decode the entire dsm frame (all contained channels)
+ *
+ * @param[in] frame_time timestamp when this dsm frame was received. Used to detect RX loss in order to reset 10/11 bit guess.
+ * @param[out] values pointer to per channel array of decoded values
+ * @param[out] num_values pointer to number of raw channel values returned
+ * @return true=DSM frame successfully decoded, false=no update
+ */
 static bool
 dsm_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values)
 {
-
 	/*
-		debug("DSM frame %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x",
-		      frame[0], frame[1], frame[2], frame[3], frame[4], frame[5], frame[6], frame[7],
-		      frame[8], frame[9], frame[10], frame[11], frame[12], frame[13], frame[14], frame[15]);
+	debug("DSM dsm_frame %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x %02x%02x",
+		dsm_frame[0], dsm_frame[1], dsm_frame[2], dsm_frame[3], dsm_frame[4], dsm_frame[5], dsm_frame[6], dsm_frame[7],
+		dsm_frame[8], dsm_frame[9], dsm_frame[10], dsm_frame[11], dsm_frame[12], dsm_frame[13], dsm_frame[14], dsm_frame[15]);
 	*/
 	/*
 	 * If we have lost signal for at least a second, reset the
 	 * format guessing heuristic.
 	 */
-	if (((frame_time - last_frame_time) > 1000000) && (channel_shift != 0))
+	if (((frame_time - dsm_last_frame_time) > 1000000) && (dsm_channel_shift != 0))
 		dsm_guess_format(true);
 
-	/* we have received something we think is a frame */
-	last_frame_time = frame_time;
+	/* we have received something we think is a dsm_frame */
+	dsm_last_frame_time = frame_time;
 
-	/* if we don't know the frame format, update the guessing state machine */
-	if (channel_shift == 0) {
+	/* if we don't know the dsm_frame format, update the guessing state machine */
+	if (dsm_channel_shift == 0) {
 		dsm_guess_format(false);
 		return false;
 	}
@@ -337,17 +334,17 @@ dsm_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values)
 	 * 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
+	 * second dsm_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)];
+		uint8_t *dp = &dsm_frame[2 + (2 * i)];
 		uint16_t raw = (dp[0] << 8) | dp[1];
 		unsigned channel, value;
 
-		if (!dsm_decode_channel(raw, channel_shift, &channel, &value))
+		if (!dsm_decode_channel(raw, dsm_channel_shift, &channel, &value))
 			continue;
 
 		/* ignore channels out of range */
@@ -359,7 +356,7 @@ dsm_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values)
 			*num_values = channel + 1;
 
 		/* convert 0-1024 / 0-2048 values to 1000-2000 ppm encoding in a very sloppy fashion */
-		if (channel_shift == 11)
+		if (dsm_channel_shift == 11)
 			value /= 2;
 
 		value += 998;
@@ -390,7 +387,7 @@ dsm_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values)
 		values[channel] = value;
 	}
 
-	if (channel_shift == 11)
+	if (dsm_channel_shift == 11)
 		*num_values |= 0x8000;
 
 	/*
@@ -398,3 +395,70 @@ dsm_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values)
 	 */
 	return true;
 }
+
+/**
+ * Called periodically to check for input data from the DSM UART
+ *
+ * The DSM* protocol doesn't provide any explicit framing,
+ * so we detect dsm frame boundaries by the inter-dsm frame delay.
+ * The minimum dsm frame spacing is 11ms; with 16 bytes at 115200bps
+ * dsm 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 dsm frame.
+ * In the case where byte(s) are dropped from a dsm frame, this also
+ * provides a degree of protection. Of course, it would be better
+ * if we didn't drop bytes...
+ * Upon receiving a full dsm frame we attempt to decode it.
+ *
+ * @param[out] values pointer to per channel array of decoded values
+ * @param[out] num_values pointer to number of raw channel values returned
+ * @return true=decoded raw channel values updated, false=no update
+ */
+bool
+dsm_input(uint16_t *values, uint16_t *num_values)
+{
+	ssize_t		ret;
+	hrt_abstime	now;
+
+	/*
+	 */
+	now = hrt_absolute_time();
+
+	if ((now - dsm_last_rx_time) > 5000) {
+		if (dsm_partial_frame_count > 0) {
+			dsm_frame_drops++;
+			dsm_partial_frame_count = 0;
+		}
+	}
+
+	/*
+	 * Fetch bytes, but no more than we would need to complete
+	 * the current dsm frame.
+	 */
+	ret = read(dsm_fd, &dsm_frame[dsm_partial_frame_count], DSM_FRAME_SIZE - dsm_partial_frame_count);
+
+	/* if the read failed for any reason, just give up here */
+	if (ret < 1)
+		return false;
+
+	dsm_last_rx_time = now;
+
+	/*
+	 * Add bytes to the current dsm frame
+	 */
+	dsm_partial_frame_count += ret;
+
+	/*
+	 * If we don't have a full dsm frame, return
+	 */
+	if (dsm_partial_frame_count < DSM_FRAME_SIZE)
+		return false;
+
+	/*
+	 * Great, it looks like we might have a dsm frame.  Go ahead and
+	 * decode it.
+	 */
+	dsm_partial_frame_count = 0;
+	return dsm_decode(now, values, num_values);
+}
diff --git a/src/modules/px4iofirmware/px4io.h b/src/modules/px4iofirmware/px4io.h
index 9eb092a63..b30d155bc 100644
--- a/src/modules/px4iofirmware/px4io.h
+++ b/src/modules/px4iofirmware/px4io.h
@@ -195,7 +195,7 @@ extern void	controls_init(void);
 extern void	controls_tick(void);
 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 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);