Intel iapx 432 manual Basic I/O Model

iAPX 432 Interface Processor Architecture Reference Manual

It is ~rtant to note that both the window and function facilities utilize and strictly enforce the standard 432 addressing and protection systems. Thus, a window provides protected access to an object, and a function provides a E.rotected way for Peripheral Subsystem software to interact with the 432 system.

1-2. BASIC I/O MODEL

As figure 1-2 illustrates, input/output operations in a 432 system are based on the notion of passing messages between 432 system processes and device tasks located in a Peripheral Subsystem. In this manual, a device task is consi.dered to be the hardware and software in the Peripheral Subsystem which is responsible for managing an I/O device. An I/O device is considered to be either a

consumer or producer of data. Thus an I/O device may be a real device (e. 9 ., a terminal), a file, or a pseudo-device (e. g., a spc:x>ler).

A message sent from a GOP process which requests I/O service contains information that describes the requested operation (e.g.,

"read file XYZ"). The device task interprets the message and carries out the operation. If an operation generates input data, the device task returns the data as a message to the originating process. The device task may also return a message to positively acknowledge completion of a request.

A very general and very powerful mechanism for passing messages between processes is inherent in the 432 architecture. A given Peripheral Subsystem may, or may not, have its own message facility, but in any case, such a facility will not be directly compatible with the 432's. By inter:PQsing a Peripheral Subsystem interface at the subsystem boundary, the standard 432 interprocess comnunication system can be made compatible with any device task (see figure 1-3).

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