dsm.cpp File Reference

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

#include <px4_config.h>
#include <board_config.h>
#include <px4_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>

Macros
#define	dsm_udelay(arg)   px4_usleep(arg)

Enumerations
enum	DSM_DECODE_STATE { DSM_DECODE_STATE_DESYNC = 0, DSM_DECODE_STATE_SYNC }

Functions
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)

Detailed Description

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

Decodes into the global PPM buffer and updates accordingly.

Function Documentation

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

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