Specifications

Product Errata 29
Revision Guide for AMD Athlon™ 64 and AMD Opteron™ Processors
25759 Rev. 3.79 July 2009
64 Single Step Across I/O SMI Skips One Debug Trap
Description
When single stepping (with EFLAGS.TF) across an IN or OUT instruction that detects an SMI, the
processor correctly defers taking the debug trap and instead enters SMM. Upon RSM (without I/O
restart), the processor should immediately enter the debug trap handler.
Under this scenario, the processor does not enter the debug trap handler but instead returns to the
instruction following the I/O instruction.
Potential Effect on System
When using the single step debug mode, following an I/O operation that detects an SMI, one
instruction may appear to be skipped.
Suggested Workaround
None required as this is a debug limitation only. If a workaround is desired, modify the SMM handler
to detect this case and enter the debug handler directly.
Fix Planned
Yes