ISO 20211 pdf download – Space data and information transfersystems -Spacecraft Onboard lnterface Services – Device Accessservice

ISO 20211 pdf download – Space data and information transfersystems -Spacecraft Onboard lnterface Services – Device Accessservice.
Certain devices asynchronously emit values that are stored by the scrvicc.i To acquire such a value, an application providcs a device logical identifier and a value identifier, which the service resolves in order to determine the stored aluc. The service then returns the most recently stored value. Optionally, the service may emit an indication to an application when an asynchronously emitted value from a device is acquired by the service.
Optionaily, the service may indicate a timestamp associated with an acquired value. This timestamp indicates the lime the value was generated by the device, emitted by the device, or acquired by the service (which is implementation-specific).
To command (i.e., send a value to) a device, an application provides a physical device identifier and a value identifier, together with the command value to be sent. The service resolves the physical device identifier in order to determine the DAP and a UT service, and if a response is generated by the device (as some devices do not generate a response to a command). The service maps information associated with the request onto the parameters of the protocol or the underlying service’s service-access-point, e.g.. destination address and QoS parameters. The service then uses the DAP to command the device.
Figure 2-3 also illustrates how the DAS accesses dcvices using an underlying packet service or directly accesses them using a local driver. The benefit of the service is that the user is no longer concerned with the details of the location of the sensor, its physical interface, or how it is accessed (i.e., communication protocols). As a result, configuration changes invoking a change in the physical location of a device, or changes to its electrical interface, do not require changes to the application soflware using that device.
4 MANAGEMENT INFORMATION BASE
4.1 OVERVIEW
There is currently no MIB associated with this service. All management items are associated with the implcmcniation providing the sen ice. However, guidance is provided as to MIB contents in 4.3.
4.2 SPECI FICATIONS
Any protocol claiming to provide this sence in a SOIS-compliant manner shall publish its MIB as part of the protocol specification.
4.3 tIB CtIIDANCE
The MIB of the protocol providing the DAS should consider the following aspects:
Device and Value Identifier Resolution Table, as specified in 4.4.
NOTE — These aspects are not in any way an indication of the complete contents of a M113 for a protocol providing the DAS but are ofTered as guidance as to those aspects of the MIII which may relate to DAS interface.
4.4 DEVICE AND VALUE IDENTIFIER RESOLUTION TABLE
4.4.1 The Device and Value Identifier Resolution Table shall contain a set of managed parameters that map device and value identifiers onto individual DAPs, underlying services, and their associated available addressing mechanisms.
4.4.2 The table specified in 4.4.1 should indicate to the service whether or not a specific device will generate a response.
4.4.3 Any entity managing the service should be able to:
a) access the table specified in 4.4.1; and
b) update it to reflect changes in the flight hardware configuration and relocation of dci’ ices.
NOTE – Whether the Device and Value Identifier Resolution Table can be updated dynamically during service operation is not specified here. This question is an implementation issue to be decided according to the needs of the particular mission for which the service implementation is being developed.