MC68030RC33C Freescale Semiconductor, MC68030RC33C Datasheet - Page 372

• Manufacturer Part Number: MC68030RC33C
• Description: IC MPU 32BIT ENHANCED 128-PGA
• Manufacturer: Freescale Semiconductor

Specifications of MC68030RC33C

• Processor Type: M680x0 32-Bit
• Speed: 33MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 128-PGA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -

9.9.3.5 INDIRECT DESCRIPTORS. An indirect descriptor is a table descriptor re-
9,9.3.6 USING UNUSED DESCRIPTOR BITS.
MOTOROLA
the 32 (short) or 64 (long) bits available with that format. An operating system
typically uses these fields for the software flags, indicating whether the virtual
the operating system to identify the pages that are least likely to impact
An operating system can use an early termination page descriptor to map a
contiguous block of memory for each task (both program and data). The tasks
This scheme is useful when the tasks in a system consist of one or a few
sequential blocks of memory that can be swapped as a group. The operating
system memory map can treat the entire address space within these blocks
one translation table; by the use of limit fields and early termination page
descriptors, it maps complete segments of memory.
siding in a page table. It points to another page descriptor in the translation
tree. Using an indirect descriptor for a page makes the page common to
several tasks. History information for
one descriptor. Access to the page sets the used (U) bit, and a write operation
to the page sets the M (modified) bit for that page. When the operating system
the descriptor for the common page to determine its status. With other meth-
ods of page sharing, the system would have to check page tables for all
sharing tasks to determine the status of the common page.
fields of many types of descriptors are available to the operating system for
The operating system often maintains information in an unused field about
some other indication of the page's frequency of use. This information helps
system performance if they are reallocated. The system should first use
can be relocated by changing the physical address portion of the descriptor.
as a uniform virtual space available for all tasks. The system only requires
is searching for an available page, it simply checks the page table containing
its own purposes. The invalid descriptor, in particular, uses only two bits of
address space is allocated and whether an image resides on the paging
device. Also, these fields often contain the physical address of the image.
a page resident in memory. This information may be an aging counter or
physical page frames that are not allocated to a virtual page. Next it should
use pages with the longest time since the most recent access. Pages that do
not have the M (modified) bit set should be taken first, since they do not
need to be copied to the paging device (the existing image remains valid).
MC68030 USER'S MANUAL
a c o m m o n
In general, the bits in the unused
page is maintained in only
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