NEC Network Controller uPD98502 - Manual (Page 148)

CHAPTER 2 V R 4120A
148 Preliminary User’s Manual S15543EJ1V0UM
2.5.4.7 Address error exception
(1) Cause
The Address Error exception occurs when an attempt is made to execute one of the following. This exception is
not maskable.
• Execution of the LW, LWU, SW, or CACHE instruction for word data that is not located on a word boundary
• Execution of the LH, LHU, or SH instruction for half-word data that is not located on a half-word boundary
• Execution of the LD or SD instruction for double-word data that is not located on a double-word boundary
• Referencing the kernel address space in User or Supervisor mode
• Referencing the supervisor space in User mode
• Referencing an address that does not exist in the kernel, user, or supervisor address space in 64-bit Kernel,
User, or Supervisor mode
• Branching to an address that was not located on a word boundary.
(2) Processing
The common exception vector is used for this exception. The AdEL or AdES code in the Cause register is set. If
this exception has been caused by an instruction reference or load operation, AdEL is set. If it has been caused
by a store operation, AdES is set.
When this exception occurs, the BadVAddr register stores the virtual address that was not properly aligned or was
referenced in protected address space. The contents of the VPN field of the Context and EntryHi registers are
undefined, as are the contents of the EntryLo register.
The EPC register contains the address of the instruction that caused the exception. However, if this instruction is
in a branch delay slot, the EPC register contains the address of the preceding jump or branch instruction, and the
BD bit of the Cause register is set to 1.
(3) Servicing
The kernel reports the UNIX™ SIGSEGV (segmentation violation) signal to the current process, and this exception
is usually fatal.