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Notes: There are two categories of REGisters in simulators:
1) Many simulators contain every interesting simh REGisters
in single variables and use those variables directly
throughout the simulator as needed by the system being
simulated.
2) Some simulators have some of their REGisters in a single
variable, but during instruction execution, the actual
contents of that REGister is split into possibly multiple
pieces which are assembled into the single variable when
the simulator stops instruction execution and split apart
again when simulation starts executing instructions again.
An example of this case is the PSL on the VAX simulator.
In the VAX architecture, the PSL register contains the
condition code information which is a field in the PSL.
For efficiency sake, while sim_instr() is executing
instructions, the condition code is stored a separate
variable CC. Whenever sim_instr() exits, the pieces
that comprise this register are put together into the
PSL variable. This allows the PSL register to be examined
and/or deposited to directly from SCP as needed. The PDP11
simulator handles its PSW in a similar way breaking it
into pieces during sim_instr() execution and reassembling
it upon exit.
Therefore, if every REGister that an application that
uses the sim_frontpanel register APIs is always stored
in single variables (case 1 above), then front panel
access to registers can be most efficient if, at
initialization time, the simulator calls the
sim_set_stable_registers_state() API.
Having called this API allows the internals of the
frontpanel access activities to be significantly more
efficient.
24 KiB
24 KiB