modbus_slicer.c File Reference

Implementation of the modbus slicer. More...

#include "modbus_slicer.h"
#include <string.h>

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Macros
#define	MODBUS_SLICER_USECONDS_PER_SECOND   (1000000UL)
#define	MODBUS_SLICER_INT_MULTIPLY_BY_3_5(num)   ((7 * num) / 2)
#define	MODBUS_SLICER_INT_CALCULATE_20_PERCENT(num)   ((num) / 5)

Functions
void	modbus_slicer_init (modbus_slicer_t *slicer_ptr, modbus_slicer_config_t *config_ptr)
	Initialize slicer.
void	modbus_slicer_feed (modbus_slicer_t *slicer_ptr, const uint8_t *data_ptr, size_t length, int64_t timestamp_us)
	Feed data to slicer state-machine.
void	modbus_slicer_timeout (modbus_slicer_t *slicer_ptr)
	Signal frame timeout.
void	modbus_slicer_check_timeout (modbus_slicer_t *slicer_ptr)
	Check for frame timeout.

Detailed Description

Implementation of the modbus slicer.

• Pre-calculates 3.5 characters timeout
• Uses "slab pool" for buffering frames and passes it to consumers
• Copies arriving bytes to buffer
• Calls registered callback function on data/error

Macro Definition Documentation

MODBUS_SLICER_INT_CALCULATE_20_PERCENT

#define MODBUS_SLICER_INT_CALCULATE_20_PERCENT

(

num

)

((num) / 5)

Multiply a num by 20% or (1/5)

MODBUS_SLICER_INT_MULTIPLY_BY_3_5

#define MODBUS_SLICER_INT_MULTIPLY_BY_3_5

(

num

)

((7 * num) / 2)

Multiply a num by 3.5

MODBUS_SLICER_USECONDS_PER_SECOND

#define MODBUS_SLICER_USECONDS_PER_SECOND   (1000000UL)

Micro-seconds in one second

Function Documentation

modbus_slicer_check_timeout()

void modbus_slicer_check_timeout

(

modbus_slicer_t *

slicer_ptr

)

Check for frame timeout.

Check for frame timeout by comparing last received byte to current time and timeout if it exceeds 3.5 characters time

Parameters

slicer_ptr

Pointer to slicer structure

Note

Frame boundary primary determined using timing from rs485 driver layer as it's timeout threshold is set approximately 3.5 characters time

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modbus_slicer_feed()

void modbus_slicer_feed	(	modbus_slicer_t *	slicer_ptr,
		const uint8_t *	data_ptr,
		size_t	length,
		int64_t	timestamp_us
	)

Feed data to slicer state-machine.

Parameters

slicer_ptr	Pointer to slicer structure
data_ptr	Pointer to data buffer
length	Data buffer length
timestamp_us	Data timestamp

Note

A slab gets allocated here and if passed to callback function successfully it's the consumer responsibility to free it otherwise it gets freed later in the same component

Emits overflow when data is coming but buffer is exhausted

Emits no memory when there is no available buffers

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modbus_slicer_init()

void modbus_slicer_init	(	modbus_slicer_t *	slicer_ptr,
		modbus_slicer_config_t *	config_ptr
	)

Initialize slicer.

Initialize slicer by calculating 3.5 characters time using standard frame length 11-bits and baud rate used by rs485 driver

Parameters

slicer_ptr	Pointer to slicer structure
config_ptr	Pointer to slicer configuration structure

Note

Assumes standard frame length of 11-bits

Added 20% to 3.5 characters duration for timing practicality

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modbus_slicer_timeout()

void modbus_slicer_timeout

(

modbus_slicer_t *

slicer_ptr

)

Signal frame timeout.

Slice the frame since 3.5 characters time has passed and call registered callback function

Parameters

slicer_ptr

Pointer to slicer structure

Note

Intercharacter timing is not implemented here since current setup doesn't allow for 1.5 characters timeout

Frames are dropped if there is no callback registered

Callback is triggered if there is data present otherwise it is called when errors happen and slab is reused if present

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