82801FB Datasheet, PDF (245/786 Pages) Intel Corporation – Intel I/O Controller Hub 6 (ICH6) Family

Register and Memory Mapping
If a power failure occurs at any point after step 3, the system will be able to boot from the copy of
the boot block that is stored in the block below the top. This is because the TOP_SWAP bit is
backed in the RTC well.
Note: The top-block swap mode may be forced by an external strapping option (See Section 2.22.1).
When top-block swap mode is forced in this manner, the TOP_SWAP bit cannot be cleared by
software. A re-boot with the strap removed will be required to exit a forced top-block swap mode.
Note: Top-block swap mode only affects accesses to the Firmware Hub space, not feature space.
Note: The top-block swap mode has no effect on accesses below FFFE_0000h.
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Intel^® I/O Controller Hub 6 (ICH6) Family Datasheet
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