VR4102 datasheet(188/701 Pages) NEC

188 / 701 page

CHAPTER 6 EXCEPTION PROCESSING

188

6.4.14 Reserved Instruction Exception

Cause

The Reserved Instruction exception occurs when an attempt is made to execute one of the following instructions:

— Instruction with an undefined major opcode (bits 31 to 26)

— SPECIAL instruction with an undefined minor opcode (bits 5 to 0)

— REGIMM instruction with an undefined minor opcode (bits 20 to 16)

— 64-bit instructions in 32-bit User or Supervisor mode

64-bit operations are always valid in Kernel mode regardless of the value of the KX bit in the Status register. This

exception is not maskable.

Processing

The common exception vector is used for this exception, and the RI code in the ExcCode field of the Cause

The EPC register contains the address of the reserved instruction unless it is in a branch delay slot, in which case

the EPC register contains the address of the preceding branch instruction and the BD bit of the Cause register is

set to 1.

Servicing

All currently defined MIPS ISA instructions can be executed. The process executing at the time of this exception

is handled by a UNIX SIGILL/ILL_RESOP_FAULT (illegal instruction/reserved operand fault) signal. This error is

usually fatal.

6.4.15 Trap Exception

Cause

The Trap exception occurs when a TGE, TGEU, TLT, TLTU, TEQ, TNE, TGEI, TGEUI, TLTI, TLTUI, TEQI, or

TNEI instruction results in a TRUE condition. This exception is not maskable.

Processing

The common exception vector is used for this exception, and the Tr code in the ExcCode field of the Cause

The EPC register contains the address of the trap instruction causing the exception unless the instruction is in a

branch delay slot, in which case the EPC register contains the address of the preceding branch instruction and

the BD bit of the Cause register is set to 1.

Servicing

At the time of a Trap exception, the kernel reports the UNIX SIGFPE/FPE_INTOVF_TRAP (floating-point

exception/integer overflow) signal to the current process, but the exception is usually fatal.

VR4102 Datasheet(PDF) 188 Page - NEC