Intel iapx 432 manual W1NIXM OPERATIl\J

WINOOWS

3- 2. W1NIXM OPERATI(l\J

This section descr ibes the IP' s response to an address reference

that falls into the windowed subrange of an open windGl. The discussion covers random mode transfers to and from ordinary memory-based objects; the special cases of block mode, interconnect objects and function requests are covered in subsequent sections.

ADDRESS RECDGNITI(l\J

The Interface Processor m:mitors all Peripheral Subsystem address

references that fall into its range. It compares each address presented on the Peripheral Subsystem bus to the subranges of all

open windows. If an address falls into a subrange, the IP recognizes the reference and responds as described belOil. If the address does not fall into an active subrange, the IP ignores the reference and does not respond.

CCNSISrrENCY CHID<

Given that it has recognized an address reference, the IP checks it for consistency before performing the actual transfer. There is a series of these checks which are equivalent to the steps carried out by a GOP when an instruction attempts to access data in an obj ect. Although they are described here as a sequence, the hardware is able to perform same of the checks in parallel.

The IP insures that the transfer direction (as indicated by its

read/write line) is consistent with the windOil's direction attribute. The IP computes the PS transfer displacement, that is, the position of the item (byte or double-byte) relative to the base

address of the PS subrange. The visible object length is the difference between the length of the object am its base displacement (see Figure 3-2). The transfer displacement rust be less than or equal to the visible obj ect length. The sum of the physical base address and the transfer displacement rust be less

than the largest physical 432 menory address (224_1). (A rremory bounds error would indicate erroneous information in the object

table.) If any of these checks fails, the IP detects a fault and

does not perform the transfer. Figure 3-2 illustrates the constraints which the IP applies when the consistency check is

performed. Several examples of valid mappings of window onto objects are shown in Figure 3-3.

3-9