MC68030FE20C Freescale Semiconductor, MC68030FE20C Datasheet - Page 371

• Manufacturer Part Number: MC68030FE20C
• Description: IC MPU 32BIT ENHANCED 132-CQFP
• Manufacturer: Freescale Semiconductor

Specifications of MC68030FE20C

• Processor Type: M680x0 32-Bit
• Speed: 20MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 132-CQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -

9
9.9.3.3 LIMIT FIELDS Except for a table indexed by function code, every pointer
9.9.3.4 EARLY TERMINATION PAGE DESCRIPTORS. A page descriptor residing
9-70
flexibility in the operating system and saves memory in the translation tables.
table size is practical.
ten of these tasks would require 40K bytes of space for the page tables alone
ory maps. By using limit fields, each table is only as large as the number of
translation table size and table search overhead. The descriptor can use the
the system's ability to detect very large illegal (i.e., out-of-bounds) addresses.
tors and limited pointer and page table sizes prevents this problem.
and page table can have a defined limit on its size. Defining limits provides
The limit field of a table descriptor limits the size of the table to which it
requires the maximum number of possible virtual pages, this reduction in
For example, when an operating system uses 4K-byte pages and runs nu-
a 20-entry page table. The system can limit the size of each table to 80 bytes,
or 800 bytes for ten tasks. Without the limit, an operating system running
(one table per page).
Memory savings required for translation tables is especially significant for
artificial intelligence systems these systems tend to require very large mem-
active entries within it. This limit can change as the table grows. For higher
of three or four levels of tables facilitates the management of these tables.
in a pointer table is an early termination page descriptor mapping an entire
block of pages. That is, it maps a contiguous range of virtual addresses to a
contiguous range of physical addresses. For example, an operating system
could reserve a 32K-byte area for special supervisor I/O peripheral devices.
This area can be mapped with a single early termination descriptor to save
smaller than the virtual address space that the particular descriptor repre-
sents. The MC68030 creates multiple ATC entries (one for each page) for the
as the pages are accessed,
Using the full 32-bit address and reducing the table size with invalid descrip-
points. The limit can be either an upper or a lower limit, using either the
lower or higher addresses within the range of the table. Since a task seldom
merous small tasks that average 80K bytes each in size, each task requires
level tables, each table only grows as the additional entries require. The use
limit field to reduce the size of the contiguous block when the block size is
range of virtual addresses represented by the early termination descriptor
MC68030 USER'S MANUAL
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