Apple Inc.

John E Morley

Mark I Himelstein

An emulation system contains reorganized instruction code sequences for a computer, so that the native code which is used to emulate instructions that occur most frequently in a typical environment are grouped together, to thereby minimize instruction cache conflicts. A representative set of programs which operate with the emulated code are run, and statistics are recorded to determine the most frequently occurring emulated instructions. The native code which emulates these most frequently occurring instructions is then arranged so that the portions of the code are statically stored in main memory at consecutive memory locations. As a result, when the native code for a frequently occurring emulated instruction is loaded from the memory into the cache, the likelihood that the cache will contain the native code for subsequent emulated instructions is maximized, and the likelihood of cache conflicts is minimized.

Method and system for increasing cache efficiency during emulation

Memory requirements for an emulation system are reduced by generating semantic routines on demand during emulation, rather than statically storing all routines in the body of a software emulation system. The static portion of the emulator code that is loaded into the memory of the computer comprises only one copy of each different type of semantic routine. For the emulated instruction that corresponds to the one routine stored in the emulator code, a dispatch table entry comprises a pointer to the stored semantic routine. The dispatch table entries for the other emulated instructions of the same type comprise pointers to a semantic routine generator for instructions that have the same number of operands. This semantic routine generator locates the statically stored semantic routine and makes a copy of it, substituting the appropriate operands for the desired instruction in place of those in the statically stored routine. Once this modified copy of the static semantic routine has been generated and stored in memory, its address is entered into the dispatch table, in place of the pointer to the semantic routine generator. All subsequent calls to the new instruction are then emulated by using the dynamically generated semantic routine.

Software emulation system with reduced memory requirements

The execution time overhead of software emulation is reduced by selecting frequently emulated instruction sequences in the software being emulated, and translating those instruction sequences into the instruction set of the emulating processor. In a first phase, frequently repeated sequences of emulated computer code are identified and selected for translation. In a second phase, the selected sequences from the instruction set of the emulated processor are translated into equivalent sequences for the instruction set of the emulating processor. In a third phase, the instruction sequence of the emulating processor is executed in lieu of emulating the original instructions from the emulated software.

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Kapaa, HI, United States of America

John E Morley