Datasheet

Errata
Specification Update 47
AH16. Performance Monitoring Event for Number of Reference Cycles When
the Processor Is Not Halted (3CH) Does Not Count According to the
Specification
Problem: The CPU_CLK_UNHALTED performance monitor with mask 1 counts bus clock cycles
instead of counting the core clock cycles at the maximum possible ratio. The
maximum possible ratio is computed by dividing the maximum possible core
frequency by the bus frequency.
Implication: The CPU_CLK_UNHALTED performance monitor with mask 1 counts a value lower than
expected. The value is lower by exactly one multiple of the maximum possible ratio.
Workaround: Multiply the performance monitor value by the maximum possible ratio.
Status: For the steppings affected, see the Summary Tables of Changes.
AH17. Using 2M/4M Pages When A20M# Is Asserted May Result in Incorrect
Address Translations
Problem: An external A20M# pin if enabled forces address bit 20 to be masked (forced to zero)
to emulates real-address mode address wraparound at 1 megabyte. However, if all of
the following conditions are met, address bit 20 may not be masked:
 Paging is enabled
 A linear address has bit 20 set
 The address references a large page
 A20M# is enabled
Implication: When A20M# is enabled and an address references a large page the resulting
translated physical address may be incorrect. This erratum has not been observed
with any commercially available operating system.
Workaround: Operating systems should not allow A20M# to be enabled if the masking of address
bit 20 could be applied to an address that references a large page. A20M# is normally
only used with the first megabyte of memory.
Status: For the steppings affected, see the Summary Tables of Changes.