iAPX 432 Interface Processor. Architecture Reference Manual
SUBRANGE BASE AIDRESS AND SUBRANGE SIZE
A windCM's subrange is defined by a subrange base address and a subrange size, in bytes. The subra~ is the contiguous set of Peripheral SUbsystem memory addresses that are mapped by the
windCM. A Per ipheral Subsystem bus master that references an addr.ess in a subrange accesses the corresponding object in the" 432 system.
A PS subrange is defined in terms of powers of 2. The subrange size 025 a random ~e window may be specified as any power of 2 from
through 2' (i.e., 1 through 32k bytes). When wlndCM 0 is used in block mode it may sequentially access an object as large as 64K bytes. When the target object is not an i.ntegral power of 2 i.n length, the subrange will normally be specified. as the next higher }?a'1er of 2. The subrange may also be smaller than the target object, if access to the full extent of the object is not required.
Note that the size of the window is the lesser of the size of the subrange and the size of theobject. That is, a window never provides access to 432 system rnennry beyond the extent of the windCMed object, regardless of the relationship of subrange size to object size. The IP's protection system restricts a larger suhrange to behaving as though it is exactly the same size as the windowed object. Any atterrtr.?t to access locations beyond the extent of an object will cause the IP to generate a fault.
A subrange' s base address is specified as an offset in bytes from the beginning of the IP's 64K byte range in the PS. The subrange base address bears a definite relationship to the subrange's size. Given a subrange 2n bytes long, its base address must be on a
2n byte boundary. For example, the base address of a 4K suhrange must be evenly divisible by 4K. This relationship may also
be expressed as: the base address of a 2n byte subrange, expressed in binary, must contain at least n
The following cnnstraints apply to all active subranges:
ono subranges may overlap, i. e. no two subranges may'include the same Pertpheral.Subsystem address
oall subranges must "fit" within the range of addresses (up to 64Kl that the IP
occupies in the Peripheral Subsystem memory space.
