C.13 Opcodes Reserved to Compaq

The opcodes listed in Table C–18are reserved to Compaq.

Table C–18: Opcodes Reserved for Compaq

Mnemonic

 

Mnemonic

 

Mnemonic

OPC01

01

OPC02

02

OPC03

03

OPC04

04

OPC05

05

OPC06

06

OPC07

07

 

 

 

 

 

 

 

 

 

 

Programming Note:

The code points 18.4800 and 18.4C00 are reserved for adding weaker memory barrier instructions. Those code points must operate as a Memory Barrier instruction (MB 18.4000) for implementations that precede their definition as weaker memory barrier instructions. Software must use the 18.4000 code point for MB.

C.14 Unused Function Code Behavior

Unused function codes for all opcodes assigned (not reserved) in the Version 5 Alpha architec- ture specification (May 1992) produce UNPREDICTABLE but not UNDEFINED results; they are not security holes.

Unused function codes for opcodes defined as reserved in the Version 5 Alpha architecture specification produce an illegal instruction trap. Those opcodes are 01, 02, 03, 04, 05, 06, 07, 0A, 0C, 0D, 0E, 14, 19, 1B, 1C, 1D, 1E, and 1F. Unused function codes for those opcodes reserved to PALcode produce an illegal instruction trap only if not used in the PALcode environment.

Instruction Summary C–21

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Compaq ECQD2KCTE Opcodes Reserved to Compaq, Unused Function Code Behavior, OPC01 OPC02 OPC03 OPC04 OPC05 OPC06 OPC07