EP80579 Datasheet, PDF (288/1916 Pages) Intel Corporation – Intel® EP80579 Integrated Processor Product Line

Intel^® EP80579 Integrated Processor
10.7.3
Note:
Note:
Note:
Boot-Block Update Scheme
The IICH supports a “Top-Block Swap” mode that swaps the top block in the FWH (the
boot block) with another location. This allows for safe update of the Boot Block (even if
a power failure occurs). When the “top-swap” enable bit is set, inverts A16 for cycles
going to the upper two 64 Kbyte blocks in the FWH. Specifically, in this mode, accesses
to FFFF_0000h-FFFF_FFFFh are directed to FFFE_0000h-FFFE_FFFFh and vice versa.
When the Top Swap Enable bit is 0, the IICH will not invert A16. This bit is
automatically set to 0 by RTEST#, but not by PLTRST#.
The scheme is based on the concept that the top block is reserved as the “boot” block,
and the block immediately below the top block is reserved for doing boot-block
updates.
The algorithm is:
1. Software copies the top block to the block immediately below the top.
2. Software checks that the copied block is correct. This could be done by performing
a checksum calculation.
3. Software sets the “Top-Block Swap” bit. This will invert A16 for cycles going to the
FWH.
4. Software erases the top block.
5. Software writes the new top block.
6. Software checks the new top block.
7. Software clears the top-block swap bit.
8. Software sets the Top_Swap Lock-Down bit.
If a power failure occurs at any point after step 3, the system is 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.
The top-block swap mode may be forced by an external strapping option (see
Chapter 16.0, “IMCH Registers.”). When top-block swap mode is forced in this manner,
the TOP_SWAP bit cannot be cleared by software. A reboot with the strap removed will
be required to exit a forced top-block weap mode.
Top-block swap mode only affects accesses to the Firmware Hub space, not feature
space.
The top-block swap mode has no effect on accesses below FFFE_0000h.
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Intel^® EP80579 Integrated Processor Product Line Datasheet
288
August 2009
Order Number: 320066-003US