BS ISO 20216:2015 pdf download

BS ISO 20216:2015 pdf download.Space data and information transfer systems — Spacecraft onboard interface services — Device data pooling service
The DDPS provides a standard interface that enables onboard software (applications and high-level services) to access pooled data acquired from simple onboard hardware devices such as sensors and actuators, without explicitly requesting an acquisition from the real device. The benefit of the service is that its use avoids multiple acquisitions from the same device when many applications require access to the same data, the result being reduced bandwidth from the device and probably reduced CPU load. In addition, the application is no longer concerned with the periodic acquisition process, the details of the location of the devices, their physical interfaces, or how they are accessed. As a result, configuration changes involving a change in the physical location of a device, or changes to its electrical interface; do not require changes to the application software using that device. Although isolated from the details of device location and interface type, the application must still know the format of data read from the device, and the user remains responsible for correctly interpreting those formats.
2.2.1 DATA POOL AND SAMPLES
The basic concept underlying the service is that of a data pool. A data pool is a periodically acquired cache of samples of values acquired from a number of devices on the spacecraft. Applications are expected to be able to access samples from that pool, i.e., independently of the precise physical locations of the devices, without requiring detailed knowledge of the electrical interfaces to the devices, and without triggering immediate acquisitions from the devices. The data pool approach makes it easier to develop the onboard software, enables configuration changes in the spacecraft design to be easily tolerated, and increases the re-use potential of the software. The attributes of the pool are samples of values from real devices. Each sample is a set of values from a related set of devices, along with the acquisition time for that set of values. The acquisition interval for a sample is independent from all other samples in the pool. A short, application-defined ordered history of samples is held in the pool. The relationship between the data pool, the samples, and the individual values read from devices is illustrated in figure 2-3.