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FRONTPANEL: Document best performance option for REGister content query

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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.
This commit is contained in:
Mark Pizzolato 2022-12-30 16:07:12 -10:00
parent 5f98bdcce6
commit ca79faf508
1 changed files with 35 additions and 0 deletions
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sim_frontpanel.h
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@ -150,6 +150,41 @@ and
The accumulated value will range from 0 thru the
the sample_depth specified when calling
sim_panel_set_sampling_parameters().
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.
*/
int