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The distributed EIB Operating System (OS) serves remote clients over the network. In many cases, it is useful for a node also to put its services as a communication server and management server for the EIB protocol at the disposal of local clients, not just in the obvious case of the devices own internal application(s).
These extra facilities are offered in particular by standard OEM Bus Access Units (BAU), like the BCU (Bus Coupling Unit).
internal applications
To an internal application, the BAU will moreover provide CPU and memory resources, timers etc.: the application "runs in the BAU". Advanced implementations may allow lightweight asynchronous application threads.
utility library API
As part of the User Abstraction Layer, EIB standardises a Utility (or User) Library API, which provides further infrastructure to the application. Included are user timers, debouncing, arithmetic, bit logic, message handling etc. Through the API, the application may also access external application hardware, as explained in the next section.
hosting of external application hardware
Another unique feature of EIB streamlines the hosting features for application hardware or external resources: the standardised Physical External Interface (PEI).
The PEI defines both electromechanical and software services for connecting an external application module to a BAU. Via a type resistor, the application module identifies its capabilities to the application; the BAU can deal with about 20 types (including binary, analog and serial I/O) and provides the application with corresponding services (via the API).
As an extra boon, the combination API / User Layer + PEI allows the combination loadable application + application module to be used as is on any physical medium. Particularly for flush-mounted devices, engineering overhead or adjustments to production are eliminated completely, and distribution logistics simplified accordingly.
message interface for access to external resources
For the serial PEI, EIB defines an External Message Interface (EMI). The EMI server allows both a local or remote client to access external CPU or memory resources.
dual-processor design, external applications and systems
Using the EMI the other way around, an external application can now utilise the local communication stack as EIB communication server. This permits dual-processor design of EIB devices. The EMI server may be implemented optionally by EIB Bus Access Units.
Actually, this feature can be used as a general mechanism for serial interfacing to external systems. Typical examples are the BCU-based EIB RS-232 interfaces, available from several manufacturers.
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