SpaceWire Protocol ID

Steve Parkes

Space Technology Centre

University of Dundee

Scotland, UK

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Aim

The protocol identification scheme aims to allow different protocols to operate concurrently over a

SpaceWire network without them interfering with each other

To achieve this an identifier is given to each protocol Units receiving packets process and respond to them according to the protocol specified by the protocol identifier

on the packet.

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Logical Address

Logical Address always used After path address removed logical address is present Check that packet is intended for the node it arrived at Use 254 if node does not have a logical address

LogicalAddress

ProtocolID

PathAddress

LogicalAddress

ProtocolID

Logical Address with Protocol ID

Path Address with Protocol ID

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SpaceWire Protocol Identifier

LogicalAddress

ProtocolID

Logical Address with Protocol ID

Rest of Packet EOP

LogicalAddress

ProtocolID

PathAddress

Path Address with Protocol ID

Rest of Packet EOP

LogicalAddress

ProtocolID

PathAddress

Rest of Packet EOPPath

Address

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Protocol Identifier

Protocol identifier (PID) single byte immediately following logical address

PID value of zero reserved for protocol ID extension PID value of 255 is reserved

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Protocol Identifier

PIDs in range 1 to 239 assigned by the SpaceWire working group PIDs 1 upwards for recommended protocols PIDs 239 downwards for supported legacy protocols PIDs 1-239 guaranteed not to clash i.e. each supported protocol has a unique PID

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Protocol Identifier

PIDs in the range 240 to 254 available for experimental use might clash with protocols being developed by other users

Concurrent operation of different protocols only assured for protocols in the range 1 to 239

Proven protocols may be recommended for adoption by the SpaceWire working group

Once adopted given unique protocol identifier in the range 1 to 239 added to SpaceWire standard

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Ignoring unknown protocols

If packet arrives at destination with PID that is not supported (unknown) by that destination

Destination shall ignore the packet and delete it. Count of the number of packets with unknown PIDs

should be kept and made available by the destination.

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Extended Protocol Identifier

PID with value zero (00h) used to extend number of available PIDs

Two more bytes follow reserved zero PID Forming a 16-bit extended protocol identifier Allows up to 65535 protocols to be carried over a

SpaceWire network Unlikely that extended PID will be used

0ExtnPID

LogicalAddress

ExtnPID

PathAddress

0ExtnPID

LogicalAddress

ExtnPID

Logical Address with Extended Protocol ID

Path Address with Extended Protocol ID

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Extended Protocol Identifier

Implementation of the extended protocol identifier NOT mandatory

If extended protocol identifier not implement then reception of a PID of value zero shall be

ignored destination should record count of the number of

packets it received with an extended PID Extended PID with value 000000h is reserved and

shall be ignored when received.

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Extended Protocol Identifier

Extended PIDs with values in range 000001h - 0000FFh represent same protocols as non-extended PIDs with values 01h to 0FFh respectively e.g. protocol 02h is the same as protocol 000002h.

Extended protocols 000001h-0000FFh are reserved one byte IDs are used for these protocols

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Existing Protocols

Recommended 1: Remote Memory Access Protocol (RMAP) 2: SpaceWire working group working on reliable transport

protocol

Legacy 239: STUP for SMCS-332 ASIC configuration 238: Proposal for RDDP