Datasheet

Errata

80 Specification Update

AH99. Performance Monitoring Event CPU_CLK_UNHALTED.REF May Not

Count Clock Cycles According to the Processors Operating Frequency

Problem: Performance Counter MSR_PERF_FIXED_CTR2 (MSR 30BH) that counts

CPU_CLK_UNHALTED.REF clocks should count these clock cycles at a constant rate

that is determined by the maximum resolved boot frequency, as programmed by

BIOS. Due to this erratum, the rate is instead set by the maximum core-clock to bus-

clock ratio of the processor, as indicated by hardware.

Implication: No functional impact as a result of this erratum. If the maximum resolved boot

frequency as programmed by BIOS is different from the frequency implied by the

maximum core-clock to bus-clock ratio of the processor as indicated by hardware,

then the following effects may be observed:

Workaround: Performance Monitoring Event CPU_CLK_UNHALTED.REF will count at a rate different

than the TSC (Time Stamp Counter)

 When running a system with several processors that have different maximum

core-clock to bus-clock ratios, CPU_CLK_UNHALTED.REF monitoring events at

each processor will be counted at different rates and therefore will not be

comparable.

 Calculate the ratio of the rates at which the TSC and the CPU_CLK_UNHALTED.REF

performance monitoring event count (this can be done by measuring

simultaneously their counted value while executing code) and adjust the

CPU_CLK_UNHALTED.REF event count to the maximum resolved boot frequency

using this ratio.

Status: For the steppings affected, see the Summary Tables of Changes.

AH100. Store Ordering May Be Incorrect between WC and WP Memory Types

Problem: According to Intel

64 and IA-32 Architectures Software Developer's Manual, Volume

3A, Methods of Caching Available, WP (Write Protected) stores should drain the WC

(Write Combining) buffers in the same way as UC (Uncacheable) memory type stores

do. Due to this erratum, WP stores may not drain the WC buffers.

Implication: Memory ordering may be violated between WC and WP stores.

Workaround: None Identified

Status: For the steppings affected, see the Summary Tables of Changes.