Serial protocol decoder for the Spektrum DSM* family of protocols. More...

#include <px4_platform_common/px4_config.h>
#include <board_config.h>
#include <px4_platform_common/defines.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>
#include <string.h>
#include "dsm.h"
#include "spektrum_rssi.h"
#include "common_rc.h"
#include <drivers/drv_hrt.h>

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Macros
#define	dsm_udelay(arg) px4_usleep(arg)

Enumerations
enum	DSM_DECODE_STATE { DSM_DECODE_STATE_DESYNC = 0, DSM_DECODE_STATE_SYNC }

Functions
static bool	dsm_decode (hrt_abstime frame_time, uint16_t values, uint16_t num_values, bool dsm_11_bit, unsigned max_values, int8_t rssi_percent)
	Decode the entire dsm frame (all contained channels) More...

static bool	dsm_decode_channel (uint16_t raw, unsigned shift, unsigned channel, unsigned value)
	Attempt to decode a single channel raw channel datum. More...

static bool	dsm_guess_format (bool reset)
	Attempt to guess if receiving 10 or 11 bit channel values. More...

int	dsm_config (int fd)

void	dsm_proto_init ()

int	dsm_init (const char *device)
	Initialize the DSM receive functionality. More...

void	dsm_deinit ()

bool	dsm_input (int fd, uint16_t values, uint16_t num_values, bool dsm_11_bit, uint8_t n_bytes, uint8_t *bytes, int8_t rssi, unsigned max_values)
	Called periodically to check for input data from the DSM UART. More...

bool	dsm_parse (const uint64_t now, const uint8_t frame, const unsigned len, uint16_t values, uint16_t num_values, bool dsm_11_bit, unsigned frame_drops, int8_t rssi_percent, uint16_t max_channels)

Variables
static enum DSM_DECODE_STATE	dsm_decode_state = DSM_DECODE_STATE_DESYNC

static int	dsm_fd = -1
	File handle to the DSM UART. More...

static hrt_abstime	dsm_last_rx_time
	Timestamp when we last received data. More...

static hrt_abstime	dsm_last_frame_time
	Timestamp for start of last valid dsm frame. More...

static dsm_frame_t &	dsm_frame = rc_decode_buf.dsm.frame
	DSM_BUFFER_SIZE DSM dsm frame receive buffer. More...

static dsm_buf_t &	dsm_buf = rc_decode_buf.dsm.buf
	DSM_BUFFER_SIZE DSM dsm frame receive buffer. More...

static uint16_t	dsm_chan_buf [DSM_MAX_CHANNEL_COUNT]

static unsigned	dsm_partial_frame_count
	Count of bytes received for current dsm frame. More...

static unsigned	dsm_channel_shift = 0
	Channel resolution, 0=unknown, 1=10 bit, 2=11 bit. More...

static unsigned	dsm_frame_drops = 0
	Count of incomplete DSM frames. More...

static uint16_t	dsm_chan_count = 0
	DSM channel count. More...

Detailed Description

Serial protocol decoder for the Spektrum DSM* family of protocols.

Decodes into the global PPM buffer and updates accordingly.

Definition in file dsm.cpp.

Macro Definition Documentation

◆ dsm_udelay

#define dsm_udelay ( arg ) px4_usleep(arg)

Definition at line 60 of file dsm.cpp.

Referenced by dsm_deinit().

Enumeration Type Documentation

◆ DSM_DECODE_STATE

enum DSM_DECODE_STATE

Enumerator
DSM_DECODE_STATE_DESYNC
DSM_DECODE_STATE_SYNC

Definition at line 65 of file dsm.cpp.

Function Documentation

◆ dsm_config()

int dsm_config ( int fd )

Definition at line 240 of file dsm.cpp.

References dsm_guess_format(), dsm_last_rx_time, dsm_partial_frame_count, and hrt_absolute_time().

Referenced by RCInput::cycle(), and dsm_init().

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◆ dsm_decode()

bool dsm_decode	(	hrt_abstime	frame_time,
		uint16_t *	values,
		uint16_t *	num_values,
		bool *	dsm_11_bit,
		unsigned	max_values,
		int8_t *	rssi_percent
	)

static

Decode the entire dsm frame (all contained channels)

Parameters

[in]	frame_time	timestamp when this dsm frame was received. Used to detect RX loss in order to reset 10/11 bit guess.
[out]	values	pointer to per channel array of decoded values
[out]	num_values	pointer to number of raw channel values returned

Returns: true=DSM frame successfully decoded, false=no update

Definition at line 388 of file dsm.cpp.

References dsm_channel_shift, dsm_decode_channel(), dsm_frame, DSM_FRAME_CHANNELS, dsm_guess_format(), dsm_last_frame_time, DSM_MAX_CHANNEL_COUNT, and spek_dbm_to_percent().

Referenced by dsm_parse().

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◆ dsm_decode_channel()

static bool dsm_decode_channel	(	uint16_t	raw,
		unsigned	shift,
		unsigned *	channel,
		unsigned *	value
	)

static

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

Parameters

[in]	raw	16 bit raw channel value from dsm frame
[in]	shift	position of channel number in raw data
[out]	channel	pointer to returned channel number
[out]	value	pointer to returned channel value

Returns: true=raw value successfully decoded

Definition at line 112 of file dsm.cpp.

Referenced by dsm_decode(), and dsm_guess_format().

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◆ dsm_deinit()

void dsm_deinit ( void )

Definition at line 313 of file dsm.cpp.

References DSM_CMD_BIND_POWER_DOWN, DSM_CMD_BIND_POWER_UP, DSM_CMD_BIND_REINIT_UART, DSM_CMD_BIND_SEND_PULSES, DSM_CMD_BIND_SET_RX_OUT, dsm_fd, dsm_guess_format(), and dsm_udelay.

Referenced by spektrum_rc::task_main(), and RCInput::~RCInput().

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◆ dsm_guess_format()

static bool dsm_guess_format ( bool reset )

static

Attempt to guess if receiving 10 or 11 bit channel values.

Parameters

[in] reset true=reset the 10/11 bit state to unknown

Definition at line 135 of file dsm.cpp.

References dsm_channel_shift, dsm_decode_channel(), dsm_frame, and DSM_FRAME_CHANNELS.

Referenced by dsm_config(), dsm_decode(), and dsm_deinit().

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◆ dsm_init()

int dsm_init ( const char * device )

Initialize the DSM receive functionality.

Open the UART for receiving DSM frames and configure it appropriately

Parameters

[in] device Device name of DSM UART

Definition at line 293 of file dsm.cpp.

References dsm_config(), dsm_fd, and dsm_proto_init().

Referenced by controls_init(), RCInput::init(), and spektrum_rc::task_main().

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◆ dsm_input()

bool dsm_input	(	int	fd,
		uint16_t *	values,
		uint16_t *	num_values,
		bool *	dsm_11_bit,
		uint8_t *	n_bytes,
		uint8_t **	bytes,
		int8_t *	rssi,
		unsigned	max_values
	)

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.

Parameters

[out]	values	pointer to per channel array of decoded values
[out]	num_values	pointer to number of raw channel values returned, high order bit 0:10 bit data, 1:11 bit data
[out]	n_butes	number of bytes read
[out]	bytes	pointer to the buffer of read bytes
[out]	rssi	value in percent, if supported, or 127

Returns: true=decoded raw channel values updated, false=no update

Definition at line 593 of file dsm.cpp.

References dsm_buf, dsm_frame_drops, dsm_parse(), hrt_absolute_time(), hrt_abstime, and read().

Referenced by dsm_port_input().

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◆ dsm_parse()

bool dsm_parse	(	const uint64_t	now,
		const uint8_t *	frame,
		const unsigned	len,
		uint16_t *	values,
		uint16_t *	num_values,
		bool *	dsm_11_bit,
		unsigned *	frame_drops,
		int8_t *	rssi_percent,
		uint16_t	max_channels
	)

Definition at line 640 of file dsm.cpp.

References dsm_chan_buf, dsm_chan_count, dsm_decode(), dsm_decode_state, DSM_DECODE_STATE_DESYNC, DSM_DECODE_STATE_SYNC, dsm_frame, dsm_frame_drops, DSM_FRAME_SIZE, dsm_last_rx_time, and dsm_partial_frame_count.

Referenced by RCInput::cycle(), dsm_input(), RCTest::dsmTest(), and spektrum_rc::task_main().

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◆ dsm_proto_init()

void dsm_proto_init ( void )

Definition at line 273 of file dsm.cpp.

References dsm_chan_buf, dsm_chan_count, dsm_channel_shift, dsm_decode_state, DSM_DECODE_STATE_DESYNC, dsm_frame_drops, and DSM_MAX_CHANNEL_COUNT.

Referenced by dsm_init(), and RCTest::dsmTest().

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Variable Documentation

◆ dsm_buf

dsm_buf_t& dsm_buf = rc_decode_buf.dsm.buf

static

DSM_BUFFER_SIZE DSM dsm frame receive buffer.

Definition at line 74 of file dsm.cpp.

Referenced by dsm_input().

◆ dsm_chan_buf

uint16_t dsm_chan_buf[DSM_MAX_CHANNEL_COUNT]

static

Definition at line 76 of file dsm.cpp.

Referenced by dsm_parse(), and dsm_proto_init().

◆ dsm_chan_count

uint16_t dsm_chan_count = 0

static

DSM channel count.

Definition at line 80 of file dsm.cpp.

Referenced by dsm_parse(), and dsm_proto_init().

◆ dsm_channel_shift

unsigned dsm_channel_shift = 0

static

Channel resolution, 0=unknown, 1=10 bit, 2=11 bit.

Definition at line 78 of file dsm.cpp.

Referenced by dsm_decode(), dsm_guess_format(), and dsm_proto_init().

◆ dsm_decode_state

enum DSM_DECODE_STATE dsm_decode_state = DSM_DECODE_STATE_DESYNC

static

Referenced by dsm_parse(), and dsm_proto_init().

◆ dsm_fd

int dsm_fd = -1

static

File handle to the DSM UART.

Definition at line 70 of file dsm.cpp.

Referenced by dsm_deinit(), and dsm_init().

◆ dsm_frame

dsm_frame_t& dsm_frame = rc_decode_buf.dsm.frame

static

DSM_BUFFER_SIZE DSM dsm frame receive buffer.

Definition at line 73 of file dsm.cpp.

Referenced by dsm_decode(), dsm_guess_format(), and dsm_parse().

◆ dsm_frame_drops

unsigned dsm_frame_drops = 0

static

Count of incomplete DSM frames.

Definition at line 79 of file dsm.cpp.

Referenced by dsm_input(), dsm_parse(), dsm_proto_init(), and RCTest::dsmTest().

◆ dsm_last_frame_time

hrt_abstime dsm_last_frame_time

static

Timestamp for start of last valid dsm frame.

Definition at line 72 of file dsm.cpp.

Referenced by dsm_decode().

◆ dsm_last_rx_time

hrt_abstime dsm_last_rx_time

static

Timestamp when we last received data.

Definition at line 71 of file dsm.cpp.

Referenced by dsm_config(), and dsm_parse().

◆ dsm_partial_frame_count

unsigned dsm_partial_frame_count

static

Count of bytes received for current dsm frame.

Definition at line 77 of file dsm.cpp.

Referenced by dsm_config(), and dsm_parse().

Macros

Enumerations

Functions

Variables

Detailed Description

Macro Definition Documentation

◆ dsm_udelay

Enumeration Type Documentation

◆ DSM_DECODE_STATE

Function Documentation

◆ dsm_config()

◆ dsm_decode()

◆ dsm_decode_channel()

◆ dsm_deinit()

◆ dsm_guess_format()

◆ dsm_init()

◆ dsm_input()

◆ dsm_parse()

◆ dsm_proto_init()

Variable Documentation

◆ dsm_buf

◆ dsm_chan_buf

◆ dsm_chan_count

◆ dsm_channel_shift

◆ dsm_decode_state

◆ dsm_fd

◆ dsm_frame

◆ dsm_frame_drops

◆ dsm_last_frame_time

◆ dsm_last_rx_time

◆ dsm_partial_frame_count