Modbus Buffer Management

Functions
void	Modbus::buildException (uint8_t u8exception)
	This method builds an exception message.
uint16_t	Modbus::calcCRC (uint8_t u8length)
	This method calculates CRC.
uint16_t	Modbus::getErrCnt ()
	error counter
uint16_t	Modbus::getInCnt ()
	number of incoming messages
uint8_t	Modbus::getLastError ()
	get last error message
uint16_t	Modbus::getOutCnt ()
	number of outcoming messages
int8_t	Modbus::getRxBuffer ()
	This method moves Serial buffer data to the Modbus au8Buffer.
uint8_t	Modbus::getState ()
void	Modbus::sendTxBuffer ()
	This method transmits au8Buffer to Serial line. Only if u8txenpin != 0, there is a flow handling in order to keep the RS485 transceiver in output state as long as the message is being sent. This is done with UCSRxA register. The CRC is appended to the buffer before starting to send it.
uint8_t	Modbus::validateAnswer ()
	This method validates master incoming messages.
uint8_t	Modbus::validateRequest ()
	This method validates slave incoming messages.

Detailed Description

Function Documentation

buildException()

void Modbus::buildException ( uint8_t u8exception )

private

This method builds an exception message.

Definition at line 1244 of file ModbusRtu.h.

{
    uint8_t u8func = au8Buffer[FUNC]; // get the original FUNC code
 
    au8Buffer[ID] = u8id;
    au8Buffer[FUNC] = u8func + 0x80;
    au8Buffer[2] = u8exception;
    u8BufferSize = EXCEPTION_SIZE;
}

calcCRC()

uint16_t Modbus::calcCRC ( uint8_t u8length )

private

This method calculates CRC.

Returns

uint16_t calculated CRC value for the message

Definition at line 1096 of file ModbusRtu.h.

{
    unsigned int temp, temp2, flag;
    temp = 0xFFFF;
    for (unsigned char i = 0; i < u8length; i++)
    {
        temp = temp ^ au8Buffer[i];
        //  Serial.println(au8Buffer[i], DEC);
        for (unsigned char j = 1; j <= 8; j++)
        {
            flag = temp & 0x0001;
            temp >>= 1;
            if (flag)
                temp ^= 0xA001;
        }
    }
    // Reverse byte order.
    temp2 = temp >> 8;
    temp = (temp << 8) | temp2;
    temp &= 0xFFFF;
    // the returned value is already swapped
    // crcLo byte is first & crcHi byte is last
    return temp;
}

getErrCnt()

uint16_t Modbus::getErrCnt

(

)

error counter

Get errors counter value This can be useful to diagnose communication.

Returns

errors counter

Definition at line 545 of file ModbusRtu.h.

{
    return u16errCnt;
}

getInCnt()

uint16_t Modbus::getInCnt

(

)

number of incoming messages

Get input messages counter value This can be useful to diagnose communication.

Returns

input messages counter

Definition at line 519 of file ModbusRtu.h.

{
    return u16InCnt;
}

getLastError()

uint8_t Modbus::getLastError

(

)

get last error message

Get the last error in the protocol processor

@returnreturn NO_REPLY = 255 Time-out

Returns

EXC_FUNC_CODE = 1 Function code not available

EXC_ADDR_RANGE = 2 Address beyond available space for Modbus registers

EXC_REGS_QUANT = 3 Coils or registers number beyond the available space

Definition at line 575 of file ModbusRtu.h.

{
    return u8lastError;
}

getOutCnt()

uint16_t Modbus::getOutCnt

(

)

number of outcoming messages

Get transmitted messages counter value This can be useful to diagnose communication.

Returns

transmitted messages counter

Definition at line 532 of file ModbusRtu.h.

{
    return u16OutCnt;
}

getRxBuffer()

int8_t Modbus::getRxBuffer ( )

private

This method moves Serial buffer data to the Modbus au8Buffer.

Returns

buffer size if OK, ERR_BUFF_OVERFLOW if u8BufferSize >= MAX_BUFFER

Definition at line 905 of file ModbusRtu.h.

{
    boolean bBuffOverflow = false;
 
    if (u8txenpin > 1)
    {
        RS485_CLEAR_DE;
        RS485_CLEAR_RE;
        // digitalWrite( u8txenpin, LOW );
    }
 
    u8BufferSize = 0;
    if (u8serno < 4)
        while (port->available())
        {
            au8Buffer[u8BufferSize] = port->read();
            rxBuffer[u8BufferSize] = au8Buffer[u8BufferSize];
            u8BufferSize++;
 
            if (u8BufferSize >= MAX_BUFFER)
                bBuffOverflow = true;
        }
    else
        while (softPort->available())
        {
            au8Buffer[u8BufferSize] = softPort->read();
            u8BufferSize++;
 
            if (u8BufferSize >= MAX_BUFFER)
                bBuffOverflow = true;
        }
    u16InCnt++;
 
    if (bBuffOverflow)
    {
        Log.verboseln("buffer overflow: %d", u8BufferSize);
        u16errCnt++;
        return ERR_BUFF_OVERFLOW;
    }
    //Log.verboseln("getRX-Buffer : %d",u8BufferSize);
    //printHex(rxBuffer, u8BufferSize);
    rxSize = u8BufferSize;
    return u8BufferSize;
}

getState()

uint8_t Modbus::getState

(

)

Get modbus master state

Returns

= 0 IDLE, = 1 WAITING FOR ANSWER

Definition at line 561 of file ModbusRtu.h.

{
    return u8state;
}

sendTxBuffer()

void Modbus::sendTxBuffer ( )

private

This method transmits au8Buffer to Serial line. Only if u8txenpin != 0, there is a flow handling in order to keep the RS485 transceiver in output state as long as the message is being sent. This is done with UCSRxA register. The CRC is appended to the buffer before starting to send it.

Parameters

nothing

Returns

nothing

Definition at line 962 of file ModbusRtu.h.

{
    uint8_t i = 0;
 
    // append CRC to message
    uint16_t u16crc = calcCRC(u8BufferSize);
/*
    Serial.print("---- calc CRC : HEX :  ");
    Serial.print(u16crc, DEC);
    Serial.print(" - HEX : ");
    Serial.print(u16crc, HEX);
    Serial.print(" - ");
    Serial.print(u8BufferSize);
    Serial.print("\n");
    */
 
    au8Buffer[u8BufferSize] = u16crc >> 8;
    u8BufferSize++;
    au8Buffer[u8BufferSize] = u16crc & 0x00ff;
    u8BufferSize++;
 
    if (debugSend)
    {
        Serial.print("Send Hex : \t");
        for (int i = 0; i < 8; i++)
        {
            Serial.print(au8Buffer[i], HEX);
            Serial.print(" : ");
        }
        Serial.println("--------------- \n");
    }
 
    // set RS485 transceiver to transmit mode
    if (u8txenpin > 1)
    {
        switch (u8serno)
        {
#if defined(UBRR1H)
        case 1:
            UCSR1A = UCSR1A | (1 << TXC1);
            break;
#endif
 
#if defined(UBRR2H)
        case 2:
            UCSR2A = UCSR2A | (1 << TXC2);
            break;
#endif
 
#if defined(UBRR3H)
        case 3:
            UCSR3A = UCSR3A | (1 << TXC3);
            break;
#endif
        case 0:
        default:
            UCSR0A = UCSR0A | (1 << TXC0);
            break;
        }
        RS485_SET_DE;
        RS485_SET_RE;
        // digitalWrite( u8txenpin, HIGH );
    }
 
    // transfer buffer to serial line
    if (u8serno < 4)
    {
        port->write(au8Buffer, u8BufferSize);
    }
    else
    {
        softPort->write(au8Buffer, u8BufferSize);
    }
    // keep RS485 transceiver in transmit mode as long as sending
    if (u8txenpin > 1)
    {
        switch (u8serno)
        {
#if defined(UBRR1H)
        case 1:
            while (!(UCSR1A & (1 << TXC1)))
                ;
            break;
#endif
 
#if defined(UBRR2H)
        case 2:
            while (!(UCSR2A & (1 << TXC2)))
                ;
            break;
#endif
 
#if defined(UBRR3H)
        case 3:
            while (!(UCSR3A & (1 << TXC3)))
                ;
            break;
#endif
        case 0:
        default:
            while (!(UCSR0A & (1 << TXC0)))
                ;
            break;
        }
        // return RS485 transceiver to receive mode
        RS485_CLEAR_DE;
        RS485_CLEAR_RE;
        // digitalWrite( u8txenpin, LOW );
    }
    if (u8serno < 4)
        while (port->read() >= 0)
            ;
    else
        while (softPort->read() >= 0)
            ;
 
    u8BufferSize = 0;
 
    // set time-out for master
    u32timeOut = millis() + (unsigned long)u16timeOut;
 
    // increase message counter
    u16OutCnt++;
 
    currentQuery->flags = QUERY_STATE::SENT;
}

validateAnswer()

uint8_t Modbus::validateAnswer ( )

private

This method validates master incoming messages.

Returns

0 if OK, EXCEPTION if anything fails

Definition at line 1201 of file ModbusRtu.h.

{
    // check message crc vs calculated crc
    uint16_t u16MsgCRC =
        ((au8Buffer[u8BufferSize - 2] << 8) | au8Buffer[u8BufferSize - 1]); // combine the crc Low & High bytes
    if (calcCRC(u8BufferSize - 2) != u16MsgCRC)
    {
        u16errCnt++;
        return NO_REPLY;
    }
 
    // check exception
    if ((au8Buffer[FUNC] & 0x80) != 0)
    {
        u16errCnt++;
        return ERR_EXCEPTION;
    }
 
    // check fct code
    boolean isSupported = false;
    for (uint8_t i = 0; i < sizeof(fctsupported); i++)
    {
        if (fctsupported[i] == au8Buffer[FUNC])
        {
            isSupported = 1;
            break;
        }
    }
    if (!isSupported)
    {
        u16errCnt++;
        return EXC_FUNC_CODE;
    }
 
    return 0; // OK, no exception code thrown
}

validateRequest()

uint8_t Modbus::validateRequest ( )

private

This method validates slave incoming messages.

Returns

0 if OK, EXCEPTION if anything fails

Definition at line 1128 of file ModbusRtu.h.

{
    // check message crc vs calculated crc
    uint16_t u16MsgCRC =
        ((au8Buffer[u8BufferSize - 2] << 8) | au8Buffer[u8BufferSize - 1]); // combine the crc Low & High bytes
    if (calcCRC(u8BufferSize - 2) != u16MsgCRC)
    {
        u16errCnt++;
        return NO_REPLY;
    }
 
    // check fct code
    boolean isSupported = false;
    for (uint8_t i = 0; i < sizeof(fctsupported); i++)
    {
        if (fctsupported[i] == au8Buffer[FUNC])
        {
            isSupported = 1;
            break;
        }
    }
    if (!isSupported)
    {
        u16errCnt++;
        return EXC_FUNC_CODE;
    }
 
    // check start address & nb range
    uint16_t u16regs = 0;
    uint8_t u8regs;
    switch (au8Buffer[FUNC])
    {
    case MB_FC_READ_COILS:
    case MB_FC_READ_DISCRETE_INPUT:
    case MB_FC_WRITE_MULTIPLE_COILS:
        u16regs = word(au8Buffer[ADD_HI], au8Buffer[ADD_LO]) / 16;
        u16regs += word(au8Buffer[NB_HI], au8Buffer[NB_LO]) / 16;
        u8regs = (uint8_t)u16regs;
        if (u8regs > u8regsize)
            return EXC_ADDR_RANGE;
        break;
    case MB_FC_WRITE_COIL:
        u16regs = word(au8Buffer[ADD_HI], au8Buffer[ADD_LO]) / 16;
        u8regs = (uint8_t)u16regs;
        if (u8regs > u8regsize)
            return EXC_ADDR_RANGE;
        break;
    case MB_FC_WRITE_REGISTER:
        u16regs = word(au8Buffer[ADD_HI], au8Buffer[ADD_LO]);
        u8regs = (uint8_t)u16regs;
        if (u8regs > u8regsize)
            return EXC_ADDR_RANGE;
        break;
    case MB_FC_READ_REGISTERS:
    case MB_FC_READ_INPUT_REGISTER:
    case MB_FC_WRITE_MULTIPLE_REGISTERS:
        u16regs = word(au8Buffer[ADD_HI], au8Buffer[ADD_LO]);
        u16regs += word(au8Buffer[NB_HI], au8Buffer[NB_LO]);
        u8regs = (uint8_t)u16regs;
        if (u8regs > u8regsize)
            return EXC_ADDR_RANGE;
        break;
    }
    return 0; // OK, no exception code thrown
}