MC68030CRC25C Freescale Semiconductor, MC68030CRC25C Datasheet - Page 384

• Manufacturer Part Number: MC68030CRC25C
• Description: IC MPU 32BIT ENHANCED 128-PGA
• Manufacturer: Freescale Semiconductor

Specifications of MC68030CRC25C

• Processor Type: M680x0 32-Bit
• Speed: 25MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 128-PGA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -

MOTOROLA
was a read request, the page is actually invalid because the read operation
writes the page descriptor to the page table. Some systems clear virgin pages
to
frame, reads the page image into the frame, and writes the page descriptor
to the page table. Another possible type of invalid descriptor is one that
area in a virtual machine.
translation table of the task that loses the frame to show that the page is
The method a system uses to select a page frame to steal varies a great deal
from system to system. A simple system may just steal a page from the
tains a list of pages with aging counters that have overflowed. The pages on
this list are available for stealing.
these pages can be stolen without swapping out because the existing page
sider the type of request, but assigns a physical page frame to the page and
When the software flags indicate that the page is allocated and the image
has been copied to the paging device, the operating system assigns a page
requires special processing, such as one that refers to a virtual I/0 device
Obtaining a page frame for a virtual page may be an obvious
However, when no idle page frame is available, the system must steal one.
If the page in the stolen frame has been modified in memory, the system
must save the page image on the paging device. The system must alter the
allocated and swapped out. Typically, the translation table entry shows the
address of the page image on the paging device.
lowest priority task. More advanced systems select the page frame that has
in several ways. One method uses bits of the page descriptor as an aging
counter. Periodically, the operating system examines the U (used) bits and
increments the count for pages that have not been used. The system main-
Some systems keep a separate list of pages that have not been modified
since the page image was read from memory. The page frames that contain
image on the paging device remains valid.
Page stealing software can involve many dynamics of the system. It can
consider task priority, I/0 activity, working-set determinations, the number
of executing tasks, a thrashing level, and other factors.
reads unknown data. However, the example operating system does not con-
not been accessed for the longest time. This process, called aging, is done
zero.
MC68030 USER'S MANUAL
operation.
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