Intel IA-32 Manuale Utente

5-28 Vol. 3A

Trap or Fault. The exception handler can distinguish between traps or 
faults by examining the contents of DR6 and the other debug registers.

Indicates that one or more of several debug-exception conditions has been detected. Whether the
exception is a fault or a trap depends on the condition (see Table 5-3). See Chapter 18, “Debug-
ging and Performance Monitoring,” for detailed information about the debug exceptions.

None. An exception handler can examine the debug registers to determine which condition
caused the exception.

Fault — Saved contents of CS and EIP registers point to the instruction that generated the
exception.

Trap — Saved contents of CS and EIP registers point to the instruction following the instruction
that generated the exception.

Fault — A program-state change does not accompany the debug exception, because the excep-
tion occurs before the faulting instruction is executed. The program can resume normal execu-
tion upon returning from the debug exception handler.

Trap — A program-state change does accompany the debug exception, because the instruction
or task switch being executed is allowed to complete before the exception is generated.
However, the new state of the program is not corrupted and execution of the program can
continue reliably.

Instruction fetch breakpoint 

Fault

Data read or write breakpoint

Trap

I/O read or write breakpoint 

Trap

General detect condition (in conjunction with in-circuit emulation)

Fault

Single-step Trap

Task-switch

Trap