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ravisuhagravisuhag
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feat(tmdl): add TM frame support for data link
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3 files changed

+241
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3 files changed

+241
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‎pkg/tmdl/frame.go

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package tmdl
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import (
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"encoding/binary"
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"errors"
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"fmt"
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)
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// TMTransferFrame represents a CCSDS TM Space Data Link Protocol Transfer Frame.
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type TMTransferFrame struct {
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VersionNumber uint8 // 2 bits
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SpacecraftID uint16 // 10 bits
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VirtualChannelID uint8 // 6 bits
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FrameLength uint16 // Length of the frame
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FrameSecondaryHeader []byte // Optional secondary header
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DataField []byte // Main telemetry data
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OperationalControl []byte // 4-byte OCF (if used)
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FrameErrorControl uint16 // 16-bit CRC (Error Control)
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}
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// NewTMTransferFrame initializes a new TM Transfer Frame.
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func NewTMTransferFrame(scid uint16, vcid uint8, data []byte, secondaryHeader []byte, ocf []byte) (*TMTransferFrame, error) {
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if len(data) > 65535 {
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return nil, errors.New("data field exceeds maximum frame length")
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}
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frame := &TMTransferFrame{
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VersionNumber: 0b01, // Default CCSDS TM version
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SpacecraftID: scid & 0x03FF, // Mask to 10 bits
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VirtualChannelID: vcid & 0x3F, // Mask to 6 bits
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FrameLength: uint16(5 + len(secondaryHeader) + len(data) + len(ocf) + 2), // Total frame length including headers and CRC
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FrameSecondaryHeader: secondaryHeader,
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DataField: data,
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OperationalControl: ocf,
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}
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// Compute Frame Error Control (CRC-16)
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frame.FrameErrorControl = ComputeCRC(frame.EncodeWithoutFEC())
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return frame, nil
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}
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// Encode converts the TM Transfer Frame to a byte slice.
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func (tf *TMTransferFrame) Encode() []byte {
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frameData := tf.EncodeWithoutFEC()
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// Append CRC-16
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crcBytes := make([]byte, 2)
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binary.BigEndian.PutUint16(crcBytes, tf.FrameErrorControl)
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return append(frameData, crcBytes...)
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}
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// EncodeWithoutFEC converts the frame to bytes excluding the CRC field.
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func (tf *TMTransferFrame) EncodeWithoutFEC() []byte {
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header := make([]byte, 5)
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// First 5 bytes: TFVN, SCID, VCID, Length
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header[0] = (tf.VersionNumber << 6) | byte(tf.SpacecraftID>>8)
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header[1] = byte(tf.SpacecraftID & 0xFF)
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header[2] = tf.VirtualChannelID
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binary.BigEndian.PutUint16(header[3:], tf.FrameLength)
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// Assemble full frame
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frameData := append(header, tf.FrameSecondaryHeader...)
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frameData = append(frameData, tf.DataField...)
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frameData = append(frameData, tf.OperationalControl...)
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return frameData
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}
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// DecodeTMTransferFrame parses a byte slice into a TM Transfer Frame.
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func DecodeTMTransferFrame(data []byte) (*TMTransferFrame, error) {
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if len(data) < 7 {
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return nil, errors.New("frame too short to be a valid TM Transfer Frame")
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}
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// Extract Version Number, SCID, and VCID
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version := (data[0] >> 6) & 0x03
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scid := (uint16(data[0]&0x03) << 8) | uint16(data[1])
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vcid := data[2]
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// Extract Frame Length
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frameLength := binary.BigEndian.Uint16(data[3:5])
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// Check if the received frame length matches the actual data length
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if int(frameLength) != len(data) {
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return nil, fmt.Errorf("frame length mismatch: expected %d, got %d", frameLength, len(data))
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}
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// Compute and verify CRC-16
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receivedCRC := binary.BigEndian.Uint16(data[len(data)-2:])
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computedCRC := ComputeCRC(data[:len(data)-2])
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if receivedCRC != computedCRC {
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return nil, fmt.Errorf("CRC mismatch: expected %04X, got %04X", receivedCRC, computedCRC)
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}
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// Extract Data Field
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dataStart := 5
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dataEnd := len(data) - 2
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frameSecondaryHeader := []byte{}
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operationalControl := []byte{}
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// Check if Secondary Header exists (Mission-dependent)
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if dataStart < dataEnd {
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frameSecondaryHeader = data[dataStart : dataStart+2] // Assuming a 2-byte header
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dataStart += 2
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}
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// Extract Operational Control Field (OCF) if present
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if dataEnd-dataStart >= 4 {
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operationalControl = data[dataEnd-4 : dataEnd]
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dataEnd -= 4
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}
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// Extract the main Data Field
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dataField := data[dataStart:dataEnd]
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// Construct the TMTransferFrame object
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frame := &TMTransferFrame{
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VersionNumber: version,
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SpacecraftID: scid,
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VirtualChannelID: vcid,
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FrameLength: frameLength,
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FrameSecondaryHeader: frameSecondaryHeader,
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DataField: dataField,
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OperationalControl: operationalControl,
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FrameErrorControl: receivedCRC,
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}
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return frame, nil
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}

‎pkg/tmdl/frame_test.go

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package tmdl_test
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import (
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"github.com/ravisuhag/astro/pkg/tmdl"
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"testing"
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)
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func TestNewTMTransferFrame(t *testing.T) {
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scid := uint16(0x3FF)
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vcid := uint8(0x3F)
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data := []byte{0x01, 0x02, 0x03, 0x04}
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secondaryHeader := []byte{0x05, 0x06}
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ocf := []byte{0x07, 0x08, 0x09, 0x0A}
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frame, err := tmdl.NewTMTransferFrame(scid, vcid, data, secondaryHeader, ocf)
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if err != nil {
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t.Fatalf("Expected no error, got %v", err)
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}
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if frame.SpacecraftID != scid&0x03FF {
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t.Errorf("Expected SpacecraftID %v, got %v", scid&0x03FF, frame.SpacecraftID)
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}
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if frame.VirtualChannelID != vcid&0x3F {
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t.Errorf("Expected VirtualChannelID %v, got %v", vcid&0x3F, frame.VirtualChannelID)
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}
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expectedLength := uint16(5 + len(secondaryHeader) + len(data) + len(ocf) + 2)
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if frame.FrameLength != expectedLength {
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t.Errorf("Expected FrameLength %v, got %v", expectedLength, frame.FrameLength)
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}
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}
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func TestTMTransferFrame_Encode(t *testing.T) {
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scid := uint16(0x3FF)
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vcid := uint8(0x3F)
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data := []byte{0x01, 0x02, 0x03, 0x04}
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secondaryHeader := []byte{0x05, 0x06}
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ocf := []byte{0x07, 0x08, 0x09, 0x0A}
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frame, err := tmdl.NewTMTransferFrame(scid, vcid, data, secondaryHeader, ocf)
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if err != nil {
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t.Fatalf("Expected no error, got %v", err)
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}
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bytes := frame.Encode()
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if len(bytes) != int(frame.FrameLength) {
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t.Errorf("Expected byte slice length %v, got %v", frame.FrameLength, len(bytes))
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}
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}
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func TestDecodeTMTransferFrame(t *testing.T) {
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scid := uint16(0x3FF)
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vcid := uint8(0x3F)
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data := []byte{0x01, 0x02, 0x03, 0x04}
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secondaryHeader := []byte{0x05, 0x06}
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ocf := []byte{0x07, 0x08, 0x09, 0x0A}
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frame, err := tmdl.NewTMTransferFrame(scid, vcid, data, secondaryHeader, ocf)
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if err != nil {
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t.Fatalf("Expected no error, got %v", err)
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}
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bytes := frame.Encode()
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decodedFrame, err := tmdl.DecodeTMTransferFrame(bytes)
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if err != nil {
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t.Fatalf("Expected no error, got %v", err)
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}
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if decodedFrame.SpacecraftID != frame.SpacecraftID {
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t.Errorf("Expected SpacecraftID %v, got %v", frame.SpacecraftID, decodedFrame.SpacecraftID)
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}
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if decodedFrame.VirtualChannelID != frame.VirtualChannelID {
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t.Errorf("Expected VirtualChannelID %v, got %v", frame.VirtualChannelID, decodedFrame.VirtualChannelID)
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}
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if decodedFrame.FrameLength != frame.FrameLength {
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t.Errorf("Expected FrameLength %v, got %v", frame.FrameLength, decodedFrame.FrameLength)
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}
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if string(decodedFrame.DataField) != string(frame.DataField) {
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t.Errorf("Expected DataField %v, got %v", frame.DataField, decodedFrame.DataField)
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}
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if string(decodedFrame.FrameSecondaryHeader) != string(frame.FrameSecondaryHeader) {
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t.Errorf("Expected FrameSecondaryHeader %v, got %v", frame.FrameSecondaryHeader, decodedFrame.FrameSecondaryHeader)
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}
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if string(decodedFrame.OperationalControl) != string(frame.OperationalControl) {
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t.Errorf("Expected OperationalControl %v, got %v", frame.OperationalControl, decodedFrame.OperationalControl)
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}
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}

‎pkg/tmdl/utils.go

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package tmdl
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// ComputeCRC calculates a CRC-16 checksum for the given data.
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func ComputeCRC(data []byte) uint16 {
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var crc uint16 = 0xFFFF
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for _, b := range data {
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crc ^= uint16(b) << 8
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for i := 0; i < 8; i++ {
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if (crc & 0x8000) != 0 {
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crc = (crc << 1) ^ 0x1021
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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 crc
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}

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