![]() ![]() The user can set the Top-Swap pin strap and force the system to boot from the 2nd block.If an RTC well power failure is experienced during a boot block update, the system will probably not be able to boot at that point.When the top-swap strap is used, the top-swap bit will be forced to 1 (cannot be cleared by software). This would be a last resort to allow the user to get the system to boot (and avoid having to de-solder the system flash). To avoid the potentially fatal case (where the Top-Swap bit is NOT set, but the top block is not valid), a pin strap will allow forcing the top-swap bit to be set. There is one remaining unusual case that could occur if the RTC battery is not sufficiently high to maintain the RTC well. This is because the top-swap bit is backed in the RTC well. 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. Software sets the Top_Swap Lock-Down bit.This will invert the appropriate address bits for the cycles going to the SPI. Software sets the “Top-Block Swap” bit.This could be done by performing a checksum calculation. Software checks that the copied block is correct.Software copies the top block to the block immediately below the top.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. Note:This bit is automatically set to 0 by RTCRST#, but not by PLTRST#. ![]()
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