Documentation
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Overview ¶
Package framer builds CAN frames from encoded PGN payloads. It is the inverse of the read-side frame parsing in internal/adapter: where adapter.NewPacketInfo extracts NMEA 2000 metadata from a CAN ID, this package constructs CAN IDs and frames for transmission.
Index ¶
- Constants
- func BuildCANID(pgn uint32, priority uint8, source uint8, destination uint8) uint32
- func FastPacketHeader(seqID uint8, frameNum uint8) byte
- func FastPacketSeqFrame(headerByte byte) (seqID uint8, frameNum uint8)
- func FrameFastPacket(canID uint32, payload []byte, sequenceId uint8) []can.Frame
- func FrameSingle(canID uint32, payload []byte) can.Frame
- type CANID
Constants ¶
const ( // PGNISOAddressClaim is the ISO 11783 Address Claim PGN. PGNISOAddressClaim uint32 = 60928 // PGNISORequest is the ISO Request PGN. PGNISORequest uint32 = 59904 )
Protocol PGNs shared across the read/write pipeline.
const BroadcastAddr uint8 = 255
BroadcastAddr is the NMEA 2000 broadcast destination address.
Variables ¶
This section is empty.
Functions ¶
func BuildCANID ¶
BuildCANID constructs a 29-bit extended CAN ID from NMEA 2000 parameters.
CAN ID bit layout (29 bits total, extended frame format):
Bits 28-26: Priority (3 bits, 0-7, lower = higher priority) Bit 25: Reserved Bit 24: Data Page (DP) Bits 23-16: PDU Format (PF) - determines if message is broadcast or addressed Bits 15-8: PDU Specific (PS) - destination address (if PF < 240) or group extension (if PF >= 240) Bits 7-0: Source Address (SA) - the sender's address on the bus
For PDU2 (broadcast) PGNs where PF >= 240, the PGN encodes both PF and PS fields. For PDU1 (addressed) PGNs where PF < 240, the PGN's low byte is zero and the destination address is placed into the PS field (bits 15-8 of the CAN ID).
Parameters:
- pgn: The Parameter Group Number (18-bit). For PDU1 PGNs, the low byte must be 0.
- priority: Message priority (0-7). Only the lower 3 bits are used.
- source: Source address of the transmitting device (0-251; 252-255 are reserved/special in NMEA 2000).
- destination: Destination address for PDU1 (addressed) PGNs. Ignored for PDU2 (broadcast) PGNs.
Returns the constructed 29-bit CAN ID.
func FastPacketHeader ¶
FastPacketHeader builds a fast-packet header byte from a sequence ID and frame number. Inverse of FastPacketSeqFrame.
func FastPacketSeqFrame ¶
FastPacketSeqFrame splits a fast-packet header byte into its 3-bit sequence ID (bits 7-5) and 5-bit frame number (bits 4-0).
func FrameFastPacket ¶
FrameFastPacket creates multiple CAN frames for fast-packet PGNs whose payload exceeds 8 bytes. The fast-packet protocol splits the payload across multiple CAN frames:
Frame 0:
- Data[0] = (sequenceId << 5) | 0 (frame counter = 0)
- Data[1] = total payload length
- Data[2:8] = first 6 bytes of payload
Continuation frames (1..N):
- Data[0] = (sequenceId << 5) | frameNumber
- Data[1:8] = next 7 bytes of payload
The sequence ID is a 3-bit counter (0-7) managed by the caller to distinguish concurrent transmissions of the same PGN. Unused bytes in the last frame are padded with 0xFF.
Parameters:
- canID: The 29-bit CAN ID constructed by BuildCANID.
- payload: The raw PGN payload bytes (up to 223 bytes).
- sequenceId: A 3-bit sequence counter (0-7) provided by the caller.
Returns a slice of can.Frame values ready for sequential transmission.
func FrameSingle ¶
FrameSingle creates a single CAN frame for payloads of 8 bytes or fewer. Payloads shorter than 8 bytes are padded with 0xFF, which is the NMEA 2000 convention for unused bytes.
Parameters:
- canID: The 29-bit CAN ID constructed by BuildCANID.
- payload: The raw PGN payload bytes (must be <= 8 bytes).
Returns a can.Frame ready for transmission.
Types ¶
type CANID ¶
CANID is the decomposed form of a 29-bit extended CAN identifier. ParseCANID and BuildCANID are inverses for the fields they share.
func ParseCANID ¶
ParseCANID extracts the NMEA 2000 fields from a 29-bit CAN ID. For PDU1 (addressed) PGNs the low byte of the raw PGN field is the destination address; it is masked off the returned PGN. For PDU2 (broadcast) PGNs the destination is BroadcastAddr.
Source Files