serial_protocol.cpp File Reference

#include <async_comm/serial.h>
#include <cstdint>
#include <cstdio>
#include <chrono>
#include <condition_variable>
#include <mutex>

Include dependency graph for serial_protocol.cpp:

Go to the source code of this file.

Macros
#define	NUM_MSGS   40000
#define	START_BYTE   0xA5
#define	START_BYTE_LEN   1
#define	PAYLOAD_LEN   12
#define	CRC_LEN   1
#define	PACKET_LEN   (START_BYTE_LEN + PAYLOAD_LEN + CRC_LEN)
#define	BAUD_RATE   921600
#define	NUM_START_BITS   1
#define	NUM_STOP_BITS   1

Enumerations
enum	ParseState { PARSE_STATE_IDLE, PARSE_STATE_GOT_START_BYTE, PARSE_STATE_GOT_PAYLOAD }
	States for the parser state machine.

Functions
uint8_t	update_crc (uint8_t inCrc, uint8_t inData)
	Recursively update the cyclic redundancy check (CRC) More...
void	pack_message (uint8_t *dst, uint32_t id, uint32_t v1, uint32_t v2)
	Pack message contents into a buffer. More...
void	unpack_payload (uint8_t *src, uint32_t *id, uint32_t *v1, uint32_t *v2)
	Unpack the contents of a message payload buffer. More...
void	parse_byte (uint8_t byte)
	Passes a received byte through the parser state machine. More...
void	callback (const uint8_t *buf, size_t len)
	Callback function for the async_comm library. More...
int	main (int argc, char **argv)

Variables
ParseState	parse_state = PARSE_STATE_IDLE
	Current state of the parser state machine.
uint8_t	receive_buffer [PAYLOAD_LEN]
	Buffer for accumulating received payload.
volatile int	receive_count = 0
	Keeps track of how many valid messages have been received.
bool	received [NUM_MSGS]
	Keeps track of which messages we've received back.
std::mutex	mutex
	mutex for synchronization between the main thread and callback thread
std::condition_variable	condition_variable
	condition variable used to suspend main thread until all messages have been received back
volatile bool	all_messages_received = false
	flag for whether all messages have been received back

Detailed Description

Author

Daniel Koch danie.nosp@m.lpko.nosp@m.ch@gm.nosp@m.ail..nosp@m.com

This example implements a simple serial protocol, and tests the async_comm library using that protocol on a serial loopback (USB-to-UART converter with the RX and TX pins connected together).

The message defined by the serial protocol has the following format:

Field	Type	Size (bytes)	Description
Start Byte		1	Identifies the beginning of a message, value is 0xA5
id	uint32_t	4	Sequential message ID
v1	uint32_t	4	The first data field
v2	uint32_t	4	The second data field
CRC	uint8_t	1	Cyclic redundancy check (CRC) byte

The "payload" of the message is the part that contains the actual data, and consists of the id, v1, and v2 fields.

The parser is implemented as a finite state machine.

Definition in file serial_protocol.cpp.

Function Documentation

callback()

void callback	(	const uint8_t *	buf,
		size_t	len
	)

Callback function for the async_comm library.

Passes the received bytes through the parser state machine.

Parameters

buf	Received bytes buffer
len	Number of bytes received

Definition at line 241 of file serial_protocol.cpp.

pack_message()

void pack_message	(	uint8_t *	dst,
		uint32_t	id,
		uint32_t	v1,
		uint32_t	v2
	)

Pack message contents into a buffer.

Parameters

[out]	dst	Buffer in which to store the message
[in]	id	ID field of the message
[in]	v1	First data field of the message
[in]	v2	Second data field of the message

Postcondition

The specified buffer contains the complete message packet, including start byte and CRC byte

Definition at line 125 of file serial_protocol.cpp.

parse_byte()

void parse_byte

(

uint8_t

byte

)

Passes a received byte through the parser state machine.

Parameters

byte	The byte to process

Definition at line 184 of file serial_protocol.cpp.

unpack_payload()

void unpack_payload	(	uint8_t *	src,
		uint32_t *	id,
		uint32_t *	v1,
		uint32_t *	v2
	)

Unpack the contents of a message payload buffer.

Parameters

[in]	src	The buffer to unpack
[out]	id	ID field of the message
[out]	v1	First data field of the message
[out]	v2	Second data field of the message

Precondition

Buffer contains a valid message payload

Postcondition

Payload contents have been placed into the specified variables

Definition at line 151 of file serial_protocol.cpp.

update_crc()

uint8_t update_crc	(	uint8_t	inCrc,
		uint8_t	inData
	)

Recursively update the cyclic redundancy check (CRC)

This uses the CRC-8-CCITT polynomial.

Source: http://www.nongnu.org/avr-libc/user-manual/group__util__crc.html#gab27eaaef6d7fd096bd7d57bf3f9ba083

Parameters

inCrc	The current CRC value. This should be initialized to 0 before processing first byte.
inData	The byte being processed

Returns

The new CRC value

Definition at line 93 of file serial_protocol.cpp.