59 lines
1.9 KiB
Go
59 lines
1.9 KiB
Go
// Package aa55 implements the GoodWe WiFi AA55-over-UDP wire protocol used by
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// the GoodWe inverter families (DT/DNS, ES/EM, ET/EH/BT/BH).
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//
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// The inverter speaks a simple request/response protocol over UDP port 8899:
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//
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// Request: [6-byte PDU body] [Modbus CRC-16, little-endian]
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// Response: AA 55 [src] 03 [byteCount] [payload…] [CRC]
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package aa55
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import (
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"errors"
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"github.com/grid-x/modbus"
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)
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// InverterAddr is the default inverter address byte, used by DT/DNS and ES/EM
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// families. ET/EH/BT/BH families require 0xF7 (247) instead.
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const InverterAddr byte = 0x7F
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// buildPDU constructs the 6-byte PDU body for a READ HOLDING REGISTERS request.
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// addr is the inverter address byte: 0x7F for DT/DNS/ES/EM, 0xF7 for ET/EH/BT/BH.
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func buildPDU(addr byte, register, count uint16) []byte {
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return []byte{
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addr, modbus.FuncCodeReadHoldingRegisters,
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byte(register >> 8), byte(register),
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byte(count >> 8), byte(count),
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}
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}
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// stripHeader validates the AA55 response frame and returns the bare payload
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// (without the 5-byte header and trailing 2-byte CRC).
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// buf[2] is the inverter source address, which varies by family — only the
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// AA 55 magic bytes and the READ HOLDING REGISTERS function code are validated.
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func stripHeader(buf []byte) ([]byte, error) {
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if len(buf) < 6 || buf[0] != 0xAA || buf[1] != 0x55 || buf[3] != modbus.FuncCodeReadHoldingRegisters {
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return nil, errors.New("invalid response header")
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}
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byteCount := int(buf[4])
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if len(buf) < 5+byteCount+2 {
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return nil, errors.New("short response")
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}
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return buf[5 : 5+byteCount], nil
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}
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// modbusCRC16 computes the Modbus CRC-16 (little-endian byte order).
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func modbusCRC16(data []byte) []byte {
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crc := uint16(0xFFFF)
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for _, b := range data {
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crc ^= uint16(b)
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for range 8 {
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if 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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}
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return []byte{byte(crc & 0xFF), byte(crc >> 8)}
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}
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