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Instruction Summary C–21
C.13 Opcodes Reserved to Compaq
The opcodes listed in Table C–18 are reserved to Compaq.
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.
Table C–18: Opcodes Reserved for Compaq
Mnemonic Mnemonic Mnemonic
OPC01 01 OPC02 02 OPC03 03
OPC04 04 OPC05 05 OPC06 06
OPC07 07