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HP OpenVMS Systemsask the wizard |
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The Question is: When I call F$GETSYI with items CPUTYPE and REAL_CPUTYPE I get different values for the same processor. Why would that be? Which one should I rely on if I want to compile with the /architecture or /optimize=tune= qualifiers? The Answer is : If you are unfamiliar with the particular Alpha microprocessor installed in your system and wish to create a program to query for this information, please see the Alpha Microprocessor example program that is posted at the Ask The Wizard website. The OpenVMS FAQ sections on the Alpha instruction set and on the use of /ARCHITECTURE and /OPTIMIZE will also be of interest here. Note that current compilers will generate AMASK-protected code sequences within loops, permitting the appropriate instruction groups to be chosen (at run-time) and executed for the current platform. The itemcode SYI$_CPUTYPE returns the type code of the current Alpha CPU (from the EXE$GQ_CPUTYPE system data cell), while SYI$_REAL_CPUTYPE returns the type code (from EXE$GQ_REAL_CPUTYPE) of the primary CPU. These may or may not be the same Alpha processor, of course. The values in these system data cells are derived from the values in the HWRPB; from the Hardware Restart Parameter Block. The EXE$GQ_CPUTYPE value is the Alpha microprocessor core used for the particular microprocessor (IMPLVER), while EXE$GQ_REAL_CPUTYPE is the particular variant of the microprocessor core. In this case, you are interested not in the CPU type (or variant), but rather in the CPU capabilities, and likely specifically interested in determining hardware support for the byte-word instruction group. This information is available via the AMASK mechanism -- see the Alpha Microprocessor example program referenced earlier for details of the AMASK and IMPLVER instructions.
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