KEY CXNCEP'IS
The Interface Processor provides a process addressing environment within the 432 system which supports the operation of the I/O controller in the 432 system. This environment is embodied as a set of system objects that ·"are used and manipulated by the IP. At any t~e, the I/O controller is represented in 432 memory by IP process obj ects am associated context obj ects. Like a GOP, the IP itself is represented by a processor object. Representing the IP and its controlling software like this creates an execution environment that is analogous to the environment of a process running on a GOP. This environment provides a standard framework for addressing, protection and conmunication within the 432 system.
Like a GOP, an IP suworts multiple process environments. The I/O controller selects the environment in which a function is to be executed. This permits, for example, the establishment of separate environments corresponding to individual device processes in the Peripheral Subsystem. If an error occurs while the IP controller is executing a function on behalf of one device task of the I/O controller, that error is confined to the associated process, and processes associated with other device tasks are not affected.
Every transfer of data between the 432 system and a Peripheral
Subsystem is performed via an IP window. A window defines a correspondence, or mapping, between a subrange of consecutive Peripheral Subsystem memory addresses (within the range of addresses occupied by the IP) and an object of system type data segment in 432 system memory (see figure
