72 lines
2.2 KiB
Go
72 lines
2.2 KiB
Go
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package xbee
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import "encoding/binary"
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// the frames have an outer shell - we will make a function that takes
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// an inner frame element and wraps it in the appropriate headers.
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// first, we should make it take the frame directly, so we make an interface
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// that represents "framable" things. note that bytes.Buffer also fulfils this.
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type Frameable interface {
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Bytes() []byte
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}
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// now we can describe our function that takes a framable and contains it + calculates checksums.
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func calculateChecksum(data []byte) byte {
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var sum byte
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for _, v := range data {
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sum += v
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}
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return 0xFF - sum
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}
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func makeXbeeApiFrame(cmd Frameable) ([]byte, error) {
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dataBuf := cmd.Bytes()
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frameBuf := make([]byte, len(dataBuf)+4)
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// move data and construct the frame
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frameBuf[0] = 0x7E // start delimiter
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// length
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// todo: check endiannes (0x7e, msb lsb)
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binary.LittleEndian.PutUint16(frameBuf[1:3], uint16(len(dataBuf)))
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copy(frameBuf[3:], dataBuf)
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chksum := calculateChecksum(dataBuf)
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frameBuf[len(frameBuf)-1] = chksum
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return frameBuf, nil
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}
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// now we can describe frames in other files that implement Frameable. this makes trasmission complete.
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// the remaining challenge is reception and actual API frames.
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// xbee uses the first byte of the "frame data" as the API identifier or command.
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//go:generate stringer -output=api_frame_cmd.go -type xbeeCmd
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type xbeeCmd byte
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const (
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// commands sent to the xbee s3b
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ATCmd xbeeCmd = 0x08 // AT Command
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ATCmdQueuePVal xbeeCmd = 0x09 // AT Command - Queue Parameter Value
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TxReq xbeeCmd = 0x10 // TX Request
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TxReqExpl xbeeCmd = 0x11 // Explicit TX Request
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RemoteCmdReq xbeeCmd = 0x17 // Remote Command Request
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// commands recieved from the xbee
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ATCmdResponse xbeeCmd = 0x88 // AT Command Response
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ModemStatus xbeeCmd = 0x8A // Modem Status
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TxStatus xbeeCmd = 0x8B // Transmit Status
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RouteInfoPkt xbeeCmd = 0x8D // Route information packet
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AddrUpdate xbeeCmd = 0x8E // Aggregate Addressing Update
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RxPkt xbeeCmd = 0x90 // RX Indicator (AO=0)
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RxPktExpl xbeeCmd = 0x91 // Explicit RX Indicator (AO=1)
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IOSample xbeeCmd = 0x92 // Data Sample RX Indicator
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NodeId xbeeCmd = 0x95 // Note Identification Indicator
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RemoteCmdResp xbeeCmd = 0x97 // Remote Command Response
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)
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