64 lines
1.4 KiB
Go
64 lines
1.4 KiB
Go
package command
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var modbusCrcTable []uint16
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func init() {
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for i := 0; i < 256; i++ {
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buffer := uint16(i << 1)
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var crc uint16
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for j := 8; j > 0; j-- {
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buffer >>= 1
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if (buffer^crc)&0x0001 != 0 {
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crc = (crc >> 1) ^ 0xA001
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} else {
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crc >>= 1
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}
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}
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modbusCrcTable = append(modbusCrcTable, crc)
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}
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}
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type ModbusCommand struct {
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payload []byte
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}
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const modbusComAddr byte = 0xf7
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type ModbusCommandType byte
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const (
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ModbusCommandTypeRead ModbusCommandType = 0x03
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ModbusCommandTypeWrite ModbusCommandType = 0x06
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ModbusCommandTypeWriteMulti ModbusCommandType = 0x10
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)
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func NewModbus(commandType ModbusCommandType, offset uint16, value uint16) *ModbusCommand {
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var p []byte
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p = append(p, modbusComAddr)
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p = append(p, byte(commandType))
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p = append(p, byte((offset>>8)&0xff))
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p = append(p, byte(offset&0xff))
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p = append(p, byte((value>>8)&0xff))
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p = append(p, byte(value&0xff))
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sum := modbusChecksum(p)
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p = append(p, byte(sum&0xff))
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p = append(p, byte((sum>>8)&0xff))
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return &ModbusCommand{payload: p}
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}
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func modbusChecksum(b []byte) uint16 {
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crc := uint16(0xffff)
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for _, v := range b {
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crc = (crc >> 8) ^ modbusCrcTable[(crc^uint16(v))&0xff]
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}
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return crc
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}
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func (cmd ModbusCommand) String() string { return string(cmd.payload) }
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func (cmd ModbusCommand) ValidateResponse(p []byte) ([]byte, error) {
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return p[5 : len(p)-2], nil
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}
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