Specification • The file access service, service type address 129 is used to read from or write to files within a file system. The currently defined file access service parameters are shown in the following table. Service Type Service Subtype Subtype Description Cmd Tlm Service Parameters Data Types and Description 129 1...
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Form Factor
Specification • While no specific form factor standard is specified in JAS it is highly recommended that programs make use of a standards-based mechanical design such as VPX defined by VITA. Although VPX is preferred, other standards may be considered for use as well. The consideration of alternate standards should carefully consider...
Fully Connected
Other • Fully connected networks are constructed by wiring every node to every other node present in the network (see Figure). For obvious reasons, these networks are the ideal topology when considering overall speed, diameter, routing complexities, reliability, and ease of construction. However, they require a massive number of links; hence, cost...
Functional Description
Profile • The Communication Profile defines standard methods for transferring data between two JAS nodes. This includes the use of protocols and packet formats by hardware and software. Applications become portable and reusable by using layered communication architecture. The applications should be agnostic to the choice of physical interconnect technology, which allows...
Functional Description
Specification • The JEEP provides efficient, best-effort delivery of packets. In-order delivery is only guaranteed if there are no transmission errors over the SpaceWire link, e.g., bit errors or dropped packets, and there are no routing options which could cause a segmented packet to be transmitted or received out of order. JEEP...
Fundamental Frequency
Specification • The first mode of the JAS mechanical structure shall be greater than 500 Hz when mounted to a rigid surface.
Gasketing
Specification • The JAS mechanical structure shall use EMI gasketing to reduce EMI emissions as appropriate for the intended application.
Generalized Star
Other • The generalized star topology is a topology that attempts to wire the network together in such a way that each node is the center of a small star (see Figure). Given a dimension d, these networks will have d! nodes and each node will have a fixed degree of d-1....
Glossary
Other • Term Definition Adaptability A system design property that refers to an architecture’s ability to be easily changed or adjusted to accommodate different system needs. Address Translation allows addresses to be translated from abstract to physical Atomic An operation during which a processor can simultaneously read a location and write it...
Gravity Release Impact
Specification • The JAS mechanical structure shall remain within given displacements as applied by determining gravity release impacts on the mechanical structure.
Grounding
Specification • Grounding provisions are required for the mechanical design to eliminate the potential for ESD charging on floating metal. Any component members with surface areas greater than 20 cm2 shall have a grounding provision. Bolted fittings are acceptable as grounding provisions if the joint meets the electrical resistance requirement for bonding....
Header
Specification • JRDDP Packet Format Destination Address The first byte of the header shall contain the Destination SpaceWire Logical Address (SLA) field that is associated with the destination TEP to which the packet is being sent. Protocol ID The second byte of the header shall contain the SpaceWire Protocol ID field and...
Humidity
Specification • The JAS housing shall meet all performance specifications during exposure to relative humidity varying from 0% to 60%.
Humidity Impact
Specification • The JAS mechanical structure shall maintain the electronics/PCBs within given displacements as applied by determining humidity impacts on the mechanical structure. If composite structures are used, the humidity should remain between a saturated composite at nominal 60% RH test area and a dry composite at 0% RH humidity vacuum environment...
Hybrid Fat Trees
Other • A hybrid fat-tree is an extension to the fat-tree topology. Hybrid fat-trees perform well when minimizing average path length and network diameter. One advantage to this design is typically about half of the nodes in this design will have a fixed degree of 2. However, other nodes have large degree,...
Interconnect Technologies
Profile • This profile describes the interconnect technologies supported by JAS. Each interconnect will be comprised of three layers based on the RapidIO standard: the Logical Layer; the Transport Layer; and the Physical Layer. The figure below shows a mapping of the interconnect layers to the OSI layers. The Application Layer is...
Interface Control
Specification • The JAS mechanical structure shall be designed to a prescribed Interface Control Drawing (ICD) as required by the application. Requirements called out in the ICD should include an answer to most of the design considerations in this specification.
JAS CCSDS SOIS
Profile • The JAS communication architecture is based on the Consultative Committee for Space Data Systems (CCSDS) Spacecraft Onboard Interface Services (SOIS) reference communication architecture. SOIS describes a layered architecture that allows applications to be abstracted from the specific communication data links. The SOIS architecture describes four layers: the Application Layer, the...
JAS Command Packet
Specification • JAS Command 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...
JAS Efficient Exchange Protocol
Profile • The JAS Efficient Exchange Protocol (JEEP) is a best-effort packet transmission protocol that can be used to send messages between applications over a SpaceWire data link. JEEP is similar to the JRDDP protocol in that provides a segmentation capability to promote fairness between all applications needing to communicate on the...
JAS Efficient Exchange Protocol
Specification • The JAS Efficient Exchange Protocol (JEEP) uses the lower level SpaceWire data link layer to provide data delivery services to one or more higher level application processes. This document specifies the functional requirements for JEEP but does not specify the interfaces to the lower or higher level processes, which may...
JAS Essential Elements
Other • The following essential elements are the minimum required to develop a JAS-compliant system. Communication Interface (physical, preferably serial) Protocols to communicate over the physical interface Network-connected nodes that implement the communication interface and protocols Network routing and addressing scheme(s) All of these items are tailorable based on recommendations in the...
JAS Packet Definition
Specification • The JAS Packet is built upon CCSDS and PUS packet standards. Some modifications were made to enforce a layered architecture in order to promote reuse of applications. The following sections will highlight these differences in more detail.
JAS Packet Protocol
Profile • The JAS Packet Protocol (JPP) provides the capability to send a single JAS Packet over a SpaceWire data link. JPP is just an encapsulation of a JAS Packet within a SpaceWire packet. Even though it is classified as a SpaceWire protocol, there are no QoS functions provided apart from those...
JAS Packet Service
Specification • Error: unable to migrate element with tag="" The CCSDS/SOIS subnetwork packet service standard can be referenced if a generic packet service is needed. The JAS Packet Service is an implementation of the CCSDS/SOIS packet service, specifically tailored for the JAS packet. The following diagram shows how the JAS Packet Service...
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