NMEA Device communication

Collaboration diagram for NMEA Device communication:

Modules
	NMEA Message support functions

Files
file	NMEAMessages.h
file	NMEASerial.h
file	NMEATypes.h

Classes
struct	nmea_msg_t
	Generic NMEA message structure. More...

Macros
#define	NMEA_SERIAL_BUFF   1024
	Default serial buffer allocation size.
#define	NMEA_START_BYTE1   0x24
	NMEA0183 Start Byte 1.
#define	NMEA_START_BYTE2   0x21
	NMEA Start Byte 2.
#define	NMEA_CSUM_MARK   0x2a
	NMEA Checksum Delimiter.
#define	NMEA_END_BYTE1   0x0d
	NMEA End Byte 1: Carriage Return.
#define	NMEA_END_BYTE2   0x0a
	NMEA End Byte 1: Line Feed.

Functions
int	nmea_openConnection (const char *port, const int baudRate)
	Set up a connection to the specified port. More...
void	nmea_closeConnection (int handle)
	Close existing connection. More...
bool	nmea_readMessage (int handle, nmea_msg_t *out)
	Static wrapper around mp_readMessage_buf. More...
bool	nmea_readMessage_buf (int handle, nmea_msg_t *out, uint8_t buf[NMEA_SERIAL_BUFF], int *index, int *hw)
	Read data from handle, and parse message if able. More...
bool	nmea_writeMessage (int handle, const nmea_msg_t *out)
	Send message to attached device. More...

Detailed Description

Function Documentation

nmea_closeConnection()

void nmea_closeConnection

(

int

handle

)

Close existing connection.

Currently just closes the file descriptor passed as handle

Parameters

[in]

handle

File descriptor opened with nmea_openConnection()

Definition at line 52 of file NMEASerial.c.

nmea_openConnection()

int nmea_openConnection	(	const char *	port,
		const int	baudRate
	)

Set up a connection to the specified port.

Currently just wraps openSerialConnection()

Parameters

[in]	port	Target character device (i.e. Serial port)
[in]	baudRate	Target baud rate

Returns

Return value of openSerialConnection()

Definition at line 43 of file NMEASerial.c.

nmea_readMessage()

bool nmea_readMessage	(	int	handle,
		nmea_msg_t *	out
	)

Static wrapper around mp_readMessage_buf.

For single threaded development and testing, uses static variables rather than requiring state to be tracked by caller.

See nmea_readMessage_buf() for full description.

Parameters

[in]	handle	File descriptor from nmea_openConnection()
[out]	out	Pointer to message structure to fill with data

Returns

True if out now contains a valid message, false otherwise.

Definition at line 66 of file NMEASerial.c.

nmea_readMessage_buf()

bool nmea_readMessage_buf	(	int	handle,
		nmea_msg_t *	out,
		uint8_t	buf[NMEA_SERIAL_BUFF],
		int *	index,
		int *	hw
	)

Read data from handle, and parse message if able.

Pulls data from handle and stores it in buf, tracking the current search position in index and the current fill level/buffer high water mark in hw

If a valid message is found then it is written to the structure provided as a parameter and the function returns true.

If a message cannot be read, the function returns false and the first byte of the raw array is set to an error value:

• 0xFF means no message found yet, and more data is required
• 0xFD is a synonym for 0xFF, but indicates that zero bytes were read from source. This could indicate EOF if reading from file, but can be ignored when streaming from a device.
• 0xAA means that an error occurred reading in data
• 0XEE means a valid message header was found, but no valid message

Parameters

[in]	handle	File descriptor from nmea_openConnection()
[out]	out	Pointer to message structure to fill with data
[in,out]	buf	Serial data buffer
[in,out]	index	Current search position within buf
[in,out]	hw	End of current valid data in buf

Returns

True if out now contains a valid message, false otherwise.

Definition at line 98 of file NMEASerial.c.

nmea_writeMessage()

bool nmea_writeMessage	(	int	handle,
		const nmea_msg_t *	out
	)

Send message to attached device.

Takes a message, validates the checksum and writes it out to the device or file connected to handle.

Parameters

[in]	handle	File descriptor from nmea_openConnection()
[in]	out	Pointer to message structure to be sent.

Returns

True if data successfullt written to handle

Definition at line 318 of file NMEASerial.c.