Intel iapx 432 manual Biock Mjde MTA Transfer

iAPX 432 Interface Processor Architecture Reference Manual

3-4.BIOCK MJDE MTA TRANSFER

Window 0 can be opened in random m::Xie or in block mode. Block mode allows the Peripheral Subsystem to take advantage of software instructions (e.g. iAPx 86 str:i.ng operations) and devices such as

~controllers, which are capable of generating consecutive address references at high speed. Block mode also oermits the transfer of a large anount of data through a small PS address subrange. For example, the full content of any object may be transferred through a one-byte or double-byte PS subrange. This helps to keep ITOre of the IP's range available for use with random mode windows.

While block mode is well-suited for the high speed transfer of large blocks of data, it provides less addressing flexibility than random

mode. When window 0 is opened in block mode, the direction attribute can specify reading or writing, but not roth. To change access directions requires closing and re-opening the window. Block mode also implies serial addressing of the windowed object. The block of data to be read or written is defined when the windCM is opened, and the whole block is transferred in sequence.

BLOCK MJlE ATl'RIBUTES

Window 0 has an additional attribute, ~ count, which is applicable only when it is opened in block IOOde. The byte count specif ies the size of the block that is to be rroved through the window. The value of this attribute may range from 0-65,535: the value represents one less than the number of bytes to be transferred (a byte count of 0 indicates that a one-byte block is to be transferred) • The byte count is independent of the subrange size. However, the IP checks to insure that the sum of the base displacement plus the byte count does not exceed the length of the target object.

The base displacement attribute locates the first byte of the block relative to the beginning of the windowed object. A value of zero indicates that the block starts at the lowest address of the object. The base displacement and byte count essentially define a refinement of the object.

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