iAPX 432 Interface Processor Architecture Reference Manual
Direct vs. Indirect Accessibility
If a copy of an access descriptor for an object is in one of t.he four entry access segments, the object it references is dir.ectly accessible. To reference such an object, two values must be specified:
o The number (0 to 3) of the entry access segment in which the access descr iptor is located, and
oThe index (0 to 16383) of the access descriptor within the specified entry access segment
When viewed from the standpoint of the 432 system and the Peripheral Subsystem, there are actually several perspectives on accessibility as srown in Table
descriptor in one of its entry access lists. In addition, by traversing access paths, the 432 processor can manipulate obj ects which are indirectly accessible.
If a copy of the access descri1;>tor is not currently in one of the four entry access segments, the desired object may be indirectly accessible. The target object may be part of a complex object structure which must be traversed by following the appropr iate access path. Once the particular access descriptor for the object has been located, the object may be made directly accessible by enter ing the access segment into one of the reuseable entry access lists
An AP has a different view of accessibility. The AP can only access 432 data through IP windows which are opened onto 432 data segments. When a window is open, the AP can use its native data manipulation operators to modify the information through the winnow. When the AP must reference data in a segment which is indirectly accessible, it issues a function request to the IP to traverse an access path to
the segment. When the data segment has been made direct]~ accessible for the AP, the IP interrupts the AP.
