dsm.cpp File Reference

#include <stdint.h>
#include <stdio.h>
#include "dsm.h"

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Macros
#define	DSM_FRAME_SIZE   16
#define	DSM_FRAME_CHANNELS   7
#define	debug(fmt, args...)   do {} while(0)

Functions
static bool	dsm_decode_channel (uint16_t raw, unsigned shift, unsigned *channel, unsigned *value)
static void	dsm_guess_format (bool reset, const uint8_t dsm_frame[16])
bool	dsm_decode (uint64_t frame_time, const uint8_t dsm_frame[16], uint16_t *values, uint16_t *num_values, uint16_t max_values)

Variables
static uint64_t	dsm_last_frame_time
static unsigned	dsm_channel_shift

Macro Definition Documentation

debug

#define debug	(		fmt,
			args...
	)		do {} while(0)

Definition at line 54 of file dsm.cpp.

Referenced by dsm_guess_format().

DSM_FRAME_CHANNELS

#define DSM_FRAME_CHANNELS   7

Max supported DSM channels

Definition at line 44 of file dsm.cpp.

Referenced by dsm_decode(), and dsm_guess_format().

DSM_FRAME_SIZE

#define DSM_FRAME_SIZE   16

DSM frame size in bytes

Definition at line 43 of file dsm.cpp.

Referenced by dsm_decode().

Function Documentation

dsm_decode()

bool dsm_decode	(	uint64_t	frame_time,
		const uint8_t	dsm_frame[16],
		uint16_t *	values,
		uint16_t *	num_values,
		uint16_t	max_values
	)

Decode the entire dsm frame (all contained channels)

Definition at line 195 of file dsm.cpp.

Referenced by F4Light::PPM_parser::_process_dsm_pulse(), Linux::RCInput::_process_dsm_pulse(), Linux::RCInput::add_dsm_input(), dsm_decode(), F4Light::DSM_parser::init(), and AP_RCProtocol_DSM::process_pulse().

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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 83 of file dsm.cpp.

Referenced by dsm_decode(), and dsm_guess_format().

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dsm_guess_format()

static void dsm_guess_format ( bool  reset, const uint8_t  dsm_frame[16]  )

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 105 of file dsm.cpp.

Referenced by dsm_decode().

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Variable Documentation

dsm_channel_shift

unsigned dsm_channel_shift

static

Channel resolution, 0=unknown, 10=10 bit, 11=11 bit

Definition at line 47 of file dsm.cpp.

Referenced by dsm_decode(), and dsm_guess_format().

dsm_last_frame_time

uint64_t dsm_last_frame_time

static

Timestamp for start of last dsm frame

Definition at line 46 of file dsm.cpp.

Referenced by dsm_decode().