ASA-EMulatR Reference Guide > Introduction > Architecture Overview > Chapter 18 – Fault Dispatcher & Precise Exceptions

18.2.1 Unified Event Carrier

PendingEvent (faultLib/PendingEvent_Refined.h, ~420 lines) is the single structure that carries all information for any exceptional event — from a DTB miss to a machine check to a CALL_PAL — through detection, queueing, and delivery. It is designed to be created at the detection point, passed to FaultDispatcher for queueing, and consumed at delivery when entering PAL mode.

18.2.2 Core Fields

Field	Purpose
cpuId	CPU this event belongs to
eventClass (EventClass)	High-level classification: None, Exception, Interrupt, MachineCheck, Reset, InternalError, SystemEvent
priority (EventPriority)	Dispatch priority: Low, Normal, High, Critical, Reset
kind (PendingEventKind)	Event type: Exception, Interrupt, Ast, MachineCheck, Reset, PalCall
exceptionClass (ExceptionClass_EV6)	Fine-grained exception type (32 values)
palVectorId (PalVectorId_EV6)	Resolved PAL vector — set at delivery time, not detection

18.2.3 Address and Context Fields

faultVA — virtual address of the faulting access (data faults) or instruction fetch (ITB faults). faultPC — program counter at the faulting instruction. asn — address space number at the time of the fault. cm — current mode (kernel/executive/supervisor/user) at the time of the event.

18.2.4 D-Stream Fault Specifics

For data-stream faults, PendingEvent carries a DStreamFaultType discriminator: DTB_MISS_SINGLE, DTB_MISS_DOUBLE_3, DTB_MISS_DOUBLE_4, DFAULT_ACV, DFAULT_FOE, DFAULT_FOW, DFAULT_FOR, UNALIGN. Additional fields include mmAccessType (Read/Write/Execute) and mmFaultReason for precise fault classification.

18.2.5 Specialized Event Fields

Arithmetic and FP: exc_Sum (arithmetic exception summary register value) and exc_Mask (arithmetic exception mask) carry the FPCR trap state needed for PAL to update EXC_SUM.

Machine Check: mcReason (MachineCheckReason), mchkCode, and mchkAddr carry the machine check diagnostic data needed by the PAL MCHK handler.

Interrupt: deviceInterruptVector, hwVector, hwIPL, swiLevel, and astMode carry the source identification needed by the PAL interrupt handler.

Extended Properties: The embedded PendingPropertyInfo struct carries detailed metadata: access type flags (isWrite, isExecute, isUnaligned, isInstruction), fault type flags (isMachineCheck, isAccessViolation, isInvalidPTE, isNonCanonical, isFaultOnExecute/Write/Read, isDoubleMiss), physical address, PTE value, and SMP fault information (initiatingCpu, participatingCpus, acknowledgedCpus, isSmpRendezvousFailure).