Intel iapx 432 manual

0BJECrS AND OPERATORS

Contained in each obj ect ' s storage descr iptor is an I/O lock which is applied by the IP when a window is opened on the object. This lock serves 'bNo purposes: first it guarantees that only one IP window can be opened on a particular 432 object at a time; second it prevents IIDvement of the object (e.g. by a memory compaction process) while it is mapped through a window.

The transfer of data between the PS and the 432 system is a three step process. First, the IP controller opens a window onto the 432 object which is to used in the transfer. In the process of opening the window the IP sets the I/O lock in the affected object. Second, the data transfer phase is entered and a PS processor transfers data

between the 432 object and the PS rnenory. Finally, when the transfer is completed, the IP controller closes the windCM and the IP clears the I/O lock in the 432 object. The storage manager in the 432 sy'stem may query the I/O lock field rut this field is not hardware-interpreted by a GOP.

As primitives in the IP hardware function set, two indivisible operators are provided which can be used to guarantee mutually exclusive access to,short ordinal fields within 432 objects. These tw:> operators, INDIVISIBLE ADD SHORI' ORDINAL and INDIVISIBLE INSERl' SHORT ORDINAL, apply an indivisible hardware operation to the specified short ordinal value. For instance, these operators might

be employed to provide a counting semaphore. These operators provide only the hardware-specific rrutual exclusion mechanisms and must be supplemented by a cx:>ordinated software discipline between processes which utilize the semaphore. For a discussion of the read-rrodify-write menory requirements for these operators, see the Intel iAPX 43203 Interface Processor Data Sheet, Order Number 171874.

2-8. CXNl'EXT ENVIRGJMENT MANIPUIATION

The I/O controller, by manipulating the context of an IP process, can access the objects which are available to the process. Like a GDP, the IP allows a context to reference any obj ect for which it holds an access descr iptor • Entry access segments contain access descriptors for all the objects which may be manipulated fran a specific process's context by an I/O controller.

The Four Entry Access Segments

Of all the access segments which can be referenced from a context, the IP provides direct access to a set of four entry access

segments. The entry access segments are referenced by access descr iptor slots 4, 5, 6 , and 7 in the context access segment. Entry access segment 0, slot 4, contains the access descr iptor for the context access segment; entry access segment O.

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