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Ski provides a functional IA-64 simulator, meaning that it simulates the
IA-64 architecture, as opposed to a particular implementation (such as
Itanium). The advantage of a functional simulator is that it executes
quickly---Ski simulatues in excess of 2 million IA-64 instructions per
second on a fast Pentium-III. On the other hand, since it doesn't
simulate the micro-architecture, it cannot be used for performance
tuning as the results would be completely meaningless. For example,
Ski simulates instructions one at a time, whereas all IA-64 chips
allow simultaneous execution of multiple instructions.
Ski simulates the complete architecture, as defined by the IA-64
architecture manuals that can be found at the following URLs:
http://developer.intel.com/design/ia-64/manuals/
http://devresource.hp.com/devresource/Docs/Refs/IA64ISA/
Ski can execute in one of two modes: system-mode or user-mode. In
system-mode, both application and system-mode execution is simulated.
In user-mode, only application-level instructions are simulated. All
system calls are intercepted and translated into corresponding calls
on the host OS (i.e., Linux/x86). Since user-mode involves less
simulation, it executes faster. On the other hand, certain things
(such as multi-threading) are not supported in user-mode execution.
Thus, for perfect simulation accuracy, it's best to use system-mode.
For more details on the internal works of the user-mode environment,
please refer to HP Labs technical report HPL-2000-85
(http://www.hpl.hp.com/techreports/2000/HPL-2000-85.html).
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