modbus.go

package modbus

import (
	"fmt"
)

type pdu struct {
	unitID       uint8
	functionCode uint8
	payload      []byte
}

// Error for modbus errors
type Error string

// Error implements the error interface.
func (me Error) Error() (s string) {
	s = string(me)
	return
}

const (
	// coils
	fcReadCoils          uint8 = 0x01
	fcWriteSingleCoil    uint8 = 0x05
	fcWriteMultipleCoils uint8 = 0x0f

	// discrete inputs
	fcReadDiscreteInputs uint8 = 0x02

	// 16-bit input/holding registers
	fcReadHoldingRegisters       uint8 = 0x03
	fcReadInputRegisters         uint8 = 0x04
	fcWriteSingleRegister        uint8 = 0x06
	fcWriteMultipleRegisters     uint8 = 0x10
	fcMaskWriteRegister          uint8 = 0x16
	fcReadWriteMultipleRegisters uint8 = 0x17
	fcReadFifoQueue              uint8 = 0x18

	// exception codes
	exIllegalFunction         uint8 = 0x01
	exIllegalDataAddress      uint8 = 0x02
	exIllegalDataValue        uint8 = 0x03
	exServerDeviceFailure     uint8 = 0x04
	exAcknowledge             uint8 = 0x05
	exServerDeviceBusy        uint8 = 0x06
	exMemoryParityError       uint8 = 0x08
	exGWPathUnavailable       uint8 = 0x0a
	exGWTargetFailedToRespond uint8 = 0x0b
)

// All Modbus errors.
const (
	ErrConfigurationError       Error = "configuration error"
	ErrRequestTimedOut          Error = "request timed out"
	ErrIllegalFunction          Error = "illegal function"
	ErrIllegalDataAddress       Error = "illegal data address"
	ErrIllegalDataValue         Error = "illegal data value"
	ErrServerDeviceFailure      Error = "server device failure"
	ErrAcknowledge              Error = "request acknowledged"
	ErrServerDeviceBusy         Error = "server device busy"
	ErrMemoryParityError        Error = "memory parity error"
	ErrGWPathUnavailable        Error = "gateway path unavailable"
	ErrGWTargetFailedToRespond  Error = "gateway target device failed to respond"
	ErrBadCRC                   Error = "bad crc"
	ErrShortFrame               Error = "short frame"
	ErrProtocolError            Error = "protocol error"
	ErrBadUnitID                Error = "bad unit id"
	ErrBadTransactionID         Error = "bad transaction id"
	ErrUnknownProtocolID        Error = "unknown protocol identifier"
	ErrUnexpectedParameters     Error = "unexpected parameters"
	ErrTransportIsAlreadyOpen   Error = "transport is already open"
	ErrTransportIsAlreadyClosed Error = "transport is already closed"
)

// mapExceptionCodeToError turns a modbus exception code into a higher level Error object.
func mapExceptionCodeToError(exceptionCode uint8) (err error) {
	switch exceptionCode {
	case exIllegalFunction:
		err = ErrIllegalFunction
	case exIllegalDataAddress:
		err = ErrIllegalDataAddress
	case exIllegalDataValue:
		err = ErrIllegalDataValue
	case exServerDeviceFailure:
		err = ErrServerDeviceFailure
	case exAcknowledge:
		err = ErrAcknowledge
	case exMemoryParityError:
		err = ErrMemoryParityError
	case exServerDeviceBusy:
		err = ErrServerDeviceBusy
	case exGWPathUnavailable:
		err = ErrGWPathUnavailable
	case exGWTargetFailedToRespond:
		err = ErrGWTargetFailedToRespond
	default:
		err = fmt.Errorf("unknown exception code (%v)", exceptionCode)
	}

	return
}

// mapErrorToExceptionCode turns an Error object into a modbus exception code.
func mapErrorToExceptionCode(err error) (exceptionCode uint8) {
	switch err {
	case ErrIllegalFunction:
		exceptionCode = exIllegalFunction
	case ErrIllegalDataAddress:
		exceptionCode = exIllegalDataAddress
	case ErrIllegalDataValue:
		exceptionCode = exIllegalDataValue
	case ErrServerDeviceFailure:
		exceptionCode = exServerDeviceFailure
	case ErrAcknowledge:
		exceptionCode = exAcknowledge
	case ErrMemoryParityError:
		exceptionCode = exMemoryParityError
	case ErrServerDeviceBusy:
		exceptionCode = exServerDeviceBusy
	case ErrGWPathUnavailable:
		exceptionCode = exGWPathUnavailable
	case ErrGWTargetFailedToRespond:
		exceptionCode = exGWTargetFailedToRespond
	default:
		exceptionCode = exServerDeviceFailure
	}

	return
}