HP 3000 Manuals

System Debug Reference Manual

Appendix C  Emulated/Translated CM Code 

Compatibility mode code segments are executed in emulation mode, unless
they have been translated by the Object Code Translator (OCT).

Emulation of an instruction can be described in the following way:

   1.  Fetch the instruction at the current program counter (CMPC).

   2.  Emulate that instruction with NM precision architecture
       instructions.

   3.  Update the program counter to point at the next instruction.

Note that multiple NM Precision Architecture instructions must be
executed during the emulation of every single CM instruction.  Besides
the obvious cost of fetching and emulating the instruction, there is
usually additional, less obvious overhead, such as indirection and
indexing, and updating STATUS register bits (that is, condition code,
carry).

                 CM Object Code

                 CM Instructions

                 +-------------+
                 | PROC+%0     |
                 | PROC+%1     |
                 | PROC+%2     |
                 | PROC+%3     |
           P >   | PROC+%4     |  ----> Fetch    PUSH S-2,X
                 | PROC+%5     |
                 | PROC+%6     |
                 | PROC+%7     |
                 | PROC+%10    |
                 | PROC+%11    |
                 | PROC+%12    |
                 | PROC+%13    |
                 | PROC+%14    |
                 | PROC+%15    |
                 | PROC+%16    |
                 +-------------+

MPE/iX 5.0 Documentation