File syn_modbus.c¶

FileList > proto > syn_modbus.c

Modbus RTU slave implementation.

#include "../util/syn_assert.h"
#include "syn_modbus.h"
#include <string.h>
#include "../util/syn_pack.h"

Public Functions¶

Type	Name
void	syn_modbus_feed (SYN_Modbus * mb, uint8_t byte) Feed a byte to the Modbus receiver.
void	syn_modbus_init (SYN_Modbus * mb, const SYN_Modbus_Config * cfg, uint8_t * buf, uint16_t buf_size) Initialize the Modbus RTU slave.
bool	syn_modbus_poll (SYN_Modbus * mb) Poll for incoming Modbus requests and process them.
bool	syn_modbus_process (SYN_Modbus * mb) Process a complete frame (call after feed + silence detection).
void	syn_modbus_reset (SYN_Modbus * mb) Reset the receiver state.

Public Static Functions¶

Type	Name
void	append_crc (uint8_t * buf, uint16_t len) Append CRC-16 Modbus to a frame buffer.
bool	check_crc (const uint8_t * buf, uint16_t len) Verify the CRC-16 Modbus trailer.
bool	get_bit (const uint8_t * bits, uint16_t idx) Helper to get bit from array.
void	handle_diagnostics (SYN_Modbus * mb, uint16_t frame_len) Handle Diagnostics (FC 0x08).
void	handle_get_comm_event_cnt (SYN_Modbus * mb) Handle Get Comm Event Counter (FC 0x0B).
void	handle_get_comm_event_log (SYN_Modbus * mb) Handle Get Comm Event Log (FC 0x0C).
void	handle_mask_write_register (SYN_Modbus * mb, uint16_t frame_len) Handle Mask Write Register (FC 0x16).
void	handle_read_bits (SYN_Modbus * mb, uint16_t frame_len, const uint8_t * bits, uint16_t total_bits) Handle Read Coils (FC 0x01) and Read Discrete Inputs (FC 0x02).
void	handle_read_device_info (SYN_Modbus * mb, uint16_t frame_len) Handle Modbus read device identification (FC 0x2B / MEI 0x0E).
void	handle_read_exception_status (SYN_Modbus * mb) Handle Modbus read exception status (FC 0x07).
void	handle_read_fifo_queue (SYN_Modbus * mb, uint16_t frame_len) Handle Read FIFO Queue (FC 0x18).
void	handle_read_file_record (SYN_Modbus * mb, uint16_t frame_len) Handle Modbus read file record (FC 0x14).
void	handle_read_regs (SYN_Modbus * mb, uint16_t frame_len, const uint16_t * regs, uint16_t reg_count) Handle Modbus read holding/input register request.
void	handle_read_write_multiple (SYN_Modbus * mb, uint16_t frame_len) Handle Modbus read/write multiple registers (FC 0x17).
void	handle_report_server_id (SYN_Modbus * mb) Handle Report Server ID (FC 0x11).
void	handle_write_file_record (SYN_Modbus * mb, uint16_t frame_len) Handle Modbus write file record (FC 0x15).
void	handle_write_multiple (SYN_Modbus * mb, uint16_t frame_len) Handle Modbus write multiple registers request.
void	handle_write_multiple_coils (SYN_Modbus * mb, uint16_t frame_len) Handle Write Multiple Coils (FC 0x0F).
void	handle_write_single (SYN_Modbus * mb, uint16_t frame_len) Handle Modbus write single register request.
void	handle_write_single_coil (SYN_Modbus * mb, uint16_t frame_len) Handle Write Single Coil (FC 0x05).
uint16_t	read_u16 (const uint8_t * buf) Read big-endian 16-bit unsigned integer from buffer.
void	send_exception (SYN_Modbus * mb, uint8_t func, uint8_t ex_code) Send a Modbus exception response.
void	send_response (SYN_Modbus * mb, uint16_t len) Append CRC and transmit a response frame.
void	set_bit (uint8_t * bits, uint16_t idx, bool val) Helper to set bit in array.
void	write_u16 (uint8_t * buf, uint16_t val) Write big-endian 16-bit unsigned integer into buffer.

Macros¶

Type	Name
define	MB_MAX_PDU_DATA `252`
define	MB_MIN_FRAME_LEN `4`
define	MB_SILENCE_MS `5`

Public Functions Documentation¶

function syn_modbus_feed¶

Feed a byte to the Modbus receiver.

void syn_modbus_feed (
    SYN_Modbus * mb,
    uint8_t byte
)

Alternative to poll() — call from UART ISR if you want interrupt-driven reception.

Parameters:

mb Modbus instance.
byte Received byte.

function syn_modbus_init¶

Initialize the Modbus RTU slave.

void syn_modbus_init (
    SYN_Modbus * mb,
    const SYN_Modbus_Config * cfg,
    uint8_t * buf,
    uint16_t buf_size
)

Parameters:

mb Modbus instance.
cfg Configuration.
buf Frame buffer (must be at least 256 bytes).
buf_size Buffer capacity.

function syn_modbus_poll¶

Poll for incoming Modbus requests and process them.

bool syn_modbus_poll (
    SYN_Modbus * mb
)

Call from your main loop. This reads bytes from UART, detects frame boundaries (3.5 character times silence), validates CRC, and processes the request.

Parameters:

mb Modbus instance.

Returns:

true if a request was processed.

function syn_modbus_process¶

Process a complete frame (call after feed + silence detection).

bool syn_modbus_process (
    SYN_Modbus * mb
)

Parameters:

mb Modbus instance.

Returns:

true if a response was sent.

function syn_modbus_reset¶

Reset the receiver state.

void syn_modbus_reset (
    SYN_Modbus * mb
)

Parameters:

mb Modbus instance.

Public Static Functions Documentation¶

function append_crc¶

Append CRC-16 Modbus to a frame buffer.

static void append_crc (
    uint8_t * buf,
    uint16_t len
)

Parameters:

buf Frame buffer.
len Frame length (excluding CRC).

function check_crc¶

Verify the CRC-16 Modbus trailer.

static bool check_crc (
    const uint8_t * buf,
    uint16_t len
)

Parameters:

buf Frame buffer.
len Total frame length (including CRC).

Returns:

true if CRC matches.

function get_bit¶

Helper to get bit from array.

static bool get_bit (
    const uint8_t * bits,
    uint16_t idx
)

Parameters:

bits Pointer to bit array.
idx Bit index.

Returns:

True if bit set, false if clear.

function handle_diagnostics¶

Handle Diagnostics (FC 0x08).

static void handle_diagnostics (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Pointer to Modbus instance.
frame_len Length of received frame.

function handle_get_comm_event_cnt¶

Handle Get Comm Event Counter (FC 0x0B).

static void handle_get_comm_event_cnt (
    SYN_Modbus * mb
)

Parameters:

mb Pointer to Modbus instance.

function handle_get_comm_event_log¶

Handle Get Comm Event Log (FC 0x0C).

static void handle_get_comm_event_log (
    SYN_Modbus * mb
)

Parameters:

mb Pointer to Modbus instance.

function handle_mask_write_register¶

Handle Mask Write Register (FC 0x16).

static void handle_mask_write_register (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Pointer to Modbus instance.
frame_len Length of received frame.

function handle_read_bits¶

Handle Read Coils (FC 0x01) and Read Discrete Inputs (FC 0x02).

static void handle_read_bits (
    SYN_Modbus * mb,
    uint16_t frame_len,
    const uint8_t * bits,
    uint16_t total_bits
)

Parameters:

mb Pointer to Modbus instance.
frame_len Length of received frame.
bits Pointer to coils or discrete inputs array.
total_bits Total available bits in array.

function handle_read_device_info¶

Handle Modbus read device identification (FC 0x2B / MEI 0x0E).

static void handle_read_device_info (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Modbus instance.
frame_len Received frame length.

function handle_read_exception_status¶

Handle Modbus read exception status (FC 0x07).

static void handle_read_exception_status (
    SYN_Modbus * mb
)

Parameters:

mb Modbus instance.

function handle_read_fifo_queue¶

Handle Read FIFO Queue (FC 0x18).

static void handle_read_fifo_queue (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Pointer to Modbus instance.
frame_len Length of received frame.

function handle_read_file_record¶

Handle Modbus read file record (FC 0x14).

static void handle_read_file_record (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Modbus instance.
frame_len Received frame length.

function handle_read_regs¶

Handle Modbus read holding/input register request.

static void handle_read_regs (
    SYN_Modbus * mb,
    uint16_t frame_len,
    const uint16_t * regs,
    uint16_t reg_count
)

Parameters:

mb Modbus instance.
frame_len Received frame length.
regs Register array.
reg_count Total register count.

function handle_read_write_multiple¶

Handle Modbus read/write multiple registers (FC 0x17).

static void handle_read_write_multiple (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Modbus instance.
frame_len Received frame length.

function handle_report_server_id¶

Handle Report Server ID (FC 0x11).

static void handle_report_server_id (
    SYN_Modbus * mb
)

Parameters:

mb Pointer to Modbus instance.

function handle_write_file_record¶

Handle Modbus write file record (FC 0x15).

static void handle_write_file_record (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Modbus instance.
frame_len Received frame length.

function handle_write_multiple¶

Handle Modbus write multiple registers request.

static void handle_write_multiple (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Modbus instance.
frame_len Received frame length.

function handle_write_multiple_coils¶

Handle Write Multiple Coils (FC 0x0F).

static void handle_write_multiple_coils (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Pointer to Modbus instance.
frame_len Length of received frame.

function handle_write_single¶

Handle Modbus write single register request.

static void handle_write_single (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Modbus instance.
frame_len Received frame length.

function handle_write_single_coil¶

Handle Write Single Coil (FC 0x05).

static void handle_write_single_coil (
    SYN_Modbus * mb,
    uint16_t frame_len
)

Parameters:

mb Pointer to Modbus instance.
frame_len Length of received frame.

function read_u16¶

Read big-endian 16-bit unsigned integer from buffer.

static inline uint16_t read_u16 (
    const uint8_t * buf
)

Parameters:

buf Pointer to 2-byte buffer.

Returns:

16-bit value.

function send_exception¶

Send a Modbus exception response.

static void send_exception (
    SYN_Modbus * mb,
    uint8_t func,
    uint8_t ex_code
)

Parameters:

mb Modbus instance.
func Function code that caused the exception.
ex_code Exception code.

function send_response¶

Append CRC and transmit a response frame.

static void send_response (
    SYN_Modbus * mb,
    uint16_t len
)

Parameters:

mb Modbus instance.
len PDU length (excluding CRC).

function set_bit¶

Helper to set bit in array.

static void set_bit (
    uint8_t * bits,
    uint16_t idx,
    bool val
)

Parameters:

bits Pointer to bit array.
idx Bit index.
val Value to set (true/false).

function write_u16¶

Write big-endian 16-bit unsigned integer into buffer.

static inline void write_u16 (
    uint8_t * buf,
    uint16_t val
)

Parameters:

buf Output buffer.
val 16-bit value to write.

Macro Definition Documentation¶

define MB_MAX_PDU_DATA¶

#define MB_MAX_PDU_DATA `252`

Max PDU data bytes.

define MB_MIN_FRAME_LEN¶

#define MB_MIN_FRAME_LEN `4`

Minimum: addr + func + CRC16.

define MB_SILENCE_MS¶

#define MB_SILENCE_MS `5`

Inter-frame silence (ms).

The documentation for this class was generated from the following file src/syntropic/proto/syn_modbus.c