iAPx 432 Interface Processor Architecture Reference Manual
Object Selectors
An object selector identifies an object by specifying an access descriptor contained in one of the four entry access segments. The object selector oonsists of a double byte quantity composed of two fields:
1.The low order two bits of the object selector specify which entry access segment holds the desired access descr iptor and are (xiled as follows:
00 - Entry Access Segment 0 (Context Access Segment)
01 - Entry Access Segment 1
10 - Entry Access Segment 2
11 - Entry Access Segment 3
2.The high order 14 bits represent a scaled index i.nto the specified entry access segment.
An object selector allows access to any of the 16,384 access descriptors from each of the 4 entry access segments. can potentially reference 65,536 (216) objects directly.
Enter ing an Access Segment
The instruction ENTER ACCESS SEGmNT allows the I/O oontroller software to enter a given access segment into Entry Access Segment 1, 2, or 3. ENTER AOCESS SEGmNT requires two operands:
oAn access descr iptor for the access segment to be entered into EASl, EAS2, or EAS3, and
oAn unsigned integer value designating the destination entry access segment, which must be 1, 2, or 3.
~ntering the Global Access Segment
Each IP process maintains a global access segment which is always accessible to the I/O controller via the ENTER GLCBAL ACCESS SEGMENT function. Imnediate entry of the global access segment allows an I/O controller to gain access to the set of process globals. The I/O oontroller needs only to specify which of the three available entry access segments is tq be used when requesting this function.
