RadiSys EPS-6315, Справочник по аппаратуре

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EPC
®
-6315 Hardware Reference
42
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Shadowing refers to the technique of copying BIOS extensions from ROM into DRAM
and accessing them from DRAM. This allows the CPU to access the BIOS extensions
much more quickly and generally increases system performance if many calls to the
BIOS extensions are made.
Cache Memory Regions:
E000–E3FF
E400–E7FF
E800–EBFF
EC00–EFFF
Memory used in the E0000h–EFFFFh DRAM region.
Determines how the system deals with specified memory
blocks or shadow
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memory. You can select one of these:
• Disabled (default) : The system does not cache memory.
• Write Back : Writes and reads to and from system
memory are cached, then written to system memory
when you perform a write-back operation.
• Select this option to reduce bus traffic by eliminating
unnecessary writes to system memory.
• This option provides the best performance, but requires
that all devices that access system memory on the system
bus be able to snoop memory accesses to ensure system
memory and cache coherency.
• Write Through : Writes and reads to and from system
memory are cached.
• Select this option for frame buffers or when there are
devices on the system bus that access system memory,
but do not perform snooping of memory accesses.
• Write Protect : Reads come from cache lines when
possible, and read misses cause cache fills. Writes
propagate to the system bus and cause corresponding
cache lines on all processors on the bus to be
invalidated. Speculative reads are allowed.
When BIOS extensions are present in these regions,
enabling caching for that region increases performance
Field Description