Specification • JAS Telemetry Packet All fields are shown in bits. The variable length application data field must be an integral number of bytes for the packet error control calculation. Spare bits may be used for padding purposes at the end to ensure the packets are an even number of bytes in...
Communication Specification
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JEEP Packet Format
Specification • All JEEP packets shall include a fixed length header, followed by a variable length payload. The figure below shows how the JEEP packet is embedded within the standard SpaceWire packet. Note that while a SpaceWire packet may have zero or more destination addresses before the JEEP header, the JEEP requires...
JRDDP Packet Format
Specification • All JRDDP packets shall include a variable length header, followed by a variable length payload, followed by a 2-byte CRC Trailer. The figure below shows how the JRDDP packet is embedded within the standard SpaceWire packet. Note that while a SpaceWire packet may have zero or more destination addresses before...
Logical Connections
Specification • Upon initialization all TEPs shall be in the CLOSED state. OPEN/RESET Command When a transmit TEP transitions to the ENABLED state (as commanded by the host), it shall send an OPEN/RESET packet to its receive TEP and initiate an acknowledgement timer. CLOSE Command When a transmit TEP transitions to the...
Memory Access Service
Specification • Error: unable to migrate element with tag="" The following diagram shows how the JAS Memory Access Service fits into the overall communication stack. The Memory Access Service provides a standard interface to applications that allows them to remotely access memory on a JAS node across a communication link. This is...
Multiplexed Logical Channels
Specification • The protocol shall support multiple simultaneous logical connections over a single SpaceWire link.
Nominal Case
Specification • In the nominal case the close packet is immediately acknowledged by the receive TEP and the transmit TEP transitions to the CLOSED state. The receive TEP transitions to the CLOSED state after the expiration of its timer. The purpose of the receive TEP’s delay in the CLOSING state is to...
Overall Functional Description
Specification • This protocol describes the mechanism for reliable transfer of data packets over a SpaceWire connection and adds the following capabilities to a SpaceWire link: Multiplexed Logical Connections Reliable Delivery Missing packet detection Out of sequence packet reordering Buffer fragmentation and reassembly
Packet Addressing and Routing
Specification • Packets will be identified and routed in the system using the SAPID, DAPID, ST, and SST. Applications shall provide these fields to the JAS Packet Service to create the stream of packets that will be sent across the communication channel. Communication channels and addresses, such as a SpaceWire address, can...
Packet Error Control
Specification • Even though JAS network protocols offer a guaranteed delivery option, there still exists the possibility of an error being introduced into a packet while it is being created or transferred from memory to the communication channel. To provide an additional layer of error detection all JAS packets shall contain a...
Packet Sequence Numbers
Specification • An 8-bit sequence number shall be assigned to each packet transmitted.
Packet Sequencing
Specification • The use of the packet sequencing fields within the JAS packet is different from the definition in the CCSDS and PUS standards. The original intention of the packet sequence counter was to provide two functions. First, it was used in combination with the sequence flags to reassemble data sets that...
Packet Service Definitions
Specification • [Placeholder: services reserved for and specific to JAS; this is a lead in to describe the services. Contact SNL if immediate support is needed with this topic. Content will be developed for JT 2.0.]
Payload
Specification • JRDDP Packet Format Secondary Header (Optional) The presence of the optional secondary header is indicated by the Secondary Header Flag in the Packet Control field. If a secondary header is present, its contents and format are implementation dependent and shall be documented in a program specific document. The secondary header...
Platform Management Service
Specification • The platform management service, service type address 130 is used to configure, manage, and monitor network specific resources. The currently defined platform management service parameters are shown in the following table. Service Type Service Subtype Subtype Description Cmd Tlm Service Parameters Data Types and Description 130 11 Network Topology Upload...
Protocols
Specification • The protocols described in the following sections are used for various SpaceWire applications depending on the needs of the communication interface. Remote Memory Access Protocol (RMAP) is a SpaceWire standard used for memory access. JAS Efficient Exchange Protocol (JEEP) and JAS Reliable Data Delivery Protocol (JRDDP) are both specific to...
Receive TEP Operations
Specification • A receive TEP shall not send DATA or CONTROL packets. It may only send ACK packets. Sliding Window The receive TEP shall maintain a sliding window, which is a range of consecutive sequence numbers that is used to determine whether each received DATA packet will be accepted or discarded. The...
Reliable Delivery
Specification • JRDDP detects lost packets, duplicate packets, out of sequence packets, and provides damaged data recovery. The protocol provides additional error detection beyond the SpaceWire physical layer by utilizing Cyclic Redundancy Checks (CRCs), packet sequence numbers, positive acknowledgement, and timeouts to detect lost or duplicated Data packets.
Remote Memory Access Protocol
Specification • JAS should use the RMAP standard to remotely access memory devices across the SpaceWire network.
Retransmission
Specification • If an ACK packet is not received by the transmit TEP within a defined channel-specific timeout interval the DATA packet shall be retransmitted.
Sequence Number Use
Specification • At the receiver TEP the sequence numbers shall be used to detect lost data packets, duplicate packets and to correctly order packets.
Serial RapidIO
Specification •
SpaceWire
Specification • The figure below defines the format of the SpaceWire packet. Following sections will discuss the details of SpaceWire Addressing, Protocol Identifiers, and the various protocols that have been developed using SpaceWire for JAS. SpaceWire Packet
SpaceWire Addressing
Specification • SpaceWire addresses shall follow the allowed allocation defined in the SpaceWire standard. Only logical addresses will be used for router and endpoint addresses which means they must be in the range of 0x20-0xFE. JAS applications shall use SpaceWire regional addressing in conjunction with header deletion within the SpaceWire routers. Two...
SpaceWire Protocol Identifiers
Specification • The standard reserves protocol identifiers in the range of 1 to 239. Protocol identifiers in the range of 240-255 can be assigned by projects. The protocol identifiers ranging from 240-250 shall be reserved for JAS protocols. A list of the protocols used by JAS is shown in the table below....
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