![](http://datasheet.mmic.net.cn/380000/-PD98501_datasheet_16745028/-PD98501_190.png)
CHAPTER 2 V
R
4120A
190
Preliminary User’s Manual S14767EJ1V0UM00
2.6.4.13 Reserved instruction exception
(1) 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
RR instruction with an undefined minor op code (bits 4 to 0) when executing the MIPS16 instruction
I8 instruction with an undefined minor op code (bits 10 to 8) when executing the MIPS16 instruction
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.
(2) Processing
The common exception vector is used for this exception, and the RI code in the ExcCode field of the Cause
register is set.
When the MIPS16 instruction is disabled, 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.
When the MIPS16 instruction is enabled, the EPC register contains the address of the instruction that caused the
exception, and the least significant bit stores the ISA mode in which an exception occurs. However, if this
instruction is in a branch delay slot or is the instruction following the Extend instruction, the EPC register contains
the address of the preceding jump or Extend instruction, and the BD bit of the Cause register is set to 1.
(3) 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.