Specification • SpaceWire is a full-duplex, point-to-point, serial data communications protocol in which the data is encoded on two differential signal pairs in each direction. This is the preferred JAS communication protocol for data rate below 200 Mbps. The electrical specifications for SpaceWire communications are described in the European Cooperation for Space...
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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 Interconnect
Profile • SpaceWire is a communication network designed to connect sensors, processing units, memory devices and telemetry/telecommand subsystems together within a spacecraft. It provides moderate-rate (2 to 200 Mbps), bi-directional, full-duplex, data links. Application, control, and time information is sent along a SpaceWire link in discrete packets. A SpaceWire network is comprised...
SpaceWire Logical
Profile • The SpaceWire standard defines packets and protocol identifiers. The SpaceWire Logical Layer has the flexibility to utilize standard or customized protocols. There are two classes of protocols available to JAS applications: Memory access protocols – access and control memory devices that are located on remote nodes within a network Messaging...
SpaceWire Physical
Profile • JAS based systems will follow the SpaceWire standard for the physical characteristics. The details of the JAS-based implementation of the SpaceWire physical layer are found in the Electrical Specification.
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....
SpaceWire Transport
Profile • The Transport Layer routes messages from one end-point processing element to another through switch processing elements. The following sections describe the various elements that define the SpaceWire Transport Layer.
Strength Qualification
Specification • The JAS mechanical structure design shall possess sufficient strength and rigidity to withstand environmental conditions defined in this document. Load Conditions
Structural Integrity
Specification • The JAS mechanical structure design shall possess sufficient strength and rigidity to withstand environmental conditions defined in this document.
Subnetwork Services
Profile • Subnetwork services provide applications with a standardized interface to network communication resources regardless of the underlying data link. These services provide applications with a single application programming interface (API) and determine the proper network protocol and data link to use. This is accomplished through parameters provided in the API calls...
Subnetwork Services
Specification • JAS Subnetwork Services provide a set of well-defined interfaces for applications to communicate across a network. They provide a layer of abstraction between the applications and the network protocols and data links, thereby allowing applications to be more portable and reusable. The services use a combination of a standard application...
Survival Temperatures
Specification • The JAS support shall meet all performance specifications after being exposed to a minimal temperature range from -40 C to +60 C.
Synchronization Service
Profile • The Synchronization Service provides the capability to send time and synchronization events to remote applications across the network. The Synchronization Service is based on the CCSDS SOIS Synchronization Service. The Synchronization Service works in conjunction with protocols to communicate time and time-based event messages to all nodes in the payload....
Synchronization Service
Specification • The following diagram shows how the JAS Synchronization Service fits into the overall communication stack. The Synchronization Service provides a standard interface to applications for sending and receiving time and event messages across a communication link. This service is typically used when the data link supports the ability to send...
System Monitor and Communication Profile
Other • The System Monitoring and Communication (SMAC) Profile defines a subsystem intended for integration into JAS nodes to provide control, communication, and state-of-health (SOH) monitoring capabilities. The SMAC subsystem consists of a single, common design applied to all nodes which provides a consistent interface to the system controller regardless of the...
TEP Parameters
Specification • Each TEP shall be defined with the following parameters: TEP Type Definition Local SLA The SLA assigned to the TEP for each channel. Remote SLA The SLA assigned to the TEP which is connected to the local TEP. TEP Type Identifies the TEP as transmit or receive. Window Size The...
TEP States
Specification • Each TEP shall be in one of four possible operating states: TEP State Definition CLOSED The TEP does not generate any packets on the link and does not respond to any packets received. ENABLED A TEP transitions to the ENABLED state when the host has requested it to be opened...
Thermal Impact
Specification • The JAS mechanical structure shall be designed to maintain the electronics/PCBs within given displacements while the system is in operation as applied by determining thermal impacts on the mechanical structure. The operational thermal environments of a nominal orbit need to be applied to the mechanical model as necessary to ensure...
Thermal Loads
Specification • Yield and ultimate thermal loads for hardware subject to thermal tests shall be calculated by either Alternate A or Alternate B, as defined below, whichever produces the maximum load. These thermal loads are not to be used for fatigue. Alternate A: Yield thermal load (YTL) = Predicted thermal load (PTL)...
Time Distribution
Other • The JAS architecture does not specify a time distribution scheme nor limit system implementations from incorporating their own methods. Two possible time distribution schemes are presented as examples: Fully Connected A fully connected distribution provides a direct interface between each node and the host. Fully connected time distribution is more...
Time Management Service
Specification • The time access service, service type address 131 is used to access and manage time. 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 131 1 Time Set X  Time Time...
Trailer
Specification • JRDDP Packet Format The JRDDP packet trailer shall be a 16-bit CCITT Cyclic Redundancy Check (CRC) computed from the Destination SLA to the last byte of the Payload field. CRC The 16-bit CCITT CRC shall be computed according to the following polynomial: CRC Polynomial for JRDDP Prior to computing each...
Transmit Priority
Specification • When more than one packet is available for transmit, all ACK packets shall be transmitted first, then CONTROL packets, then URGENT packets (if implemented), then Retransmit packets (CONTROL or DATA), then DATA packets.
Transmit TEP Operations
Specification • Transmit TEP ACKs A transmit TEP shall not send an ACK packet. Transmit TEP Sequence Number Allocation Each DATA packet transmitted shall have a sequence number allocated from the TEP's transmit window range of available sequence numbers. CONTROL Packet Sequence Number All CONTROL packets shall be transmitted with a sequence...
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