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Concepts
The emulator has been designed to ensure that the emulation-bus analyzer
and the emulation memory system will have access to the equivalent of the
internal processor 24-bit address bus, function codes, and size information.
The external bus decoder circuitry can recreate these signals for all possible
combinations of processor pin usage that make sense to the target system.
The external bus decoder must be given knowledge of how the processor
pins will be used; this knowledge is defined by the EMSIM and EMRAM
register sets.
Because the emulation-bus analyzer always receives the full 24-bit address,
the user can trace activity based upon the way the code was written, not on
the chip selects that are used to access the code. The analyzer can display
address symbols in the trace list and accept symbolic address information
entered in trace commands.
Because the emulation memory system also receives the full 24-bit address,
memory can be allocated (mapped) between the target system and emulation
(overlay) memory based upon the full address, not upon chip selects and a
subset of the full address bus. When a program download is performed, the
program information can be properly directed to emulation or target memory
based upon the full 24-bit address contained in the executable file.
The concept of register copies has been implemented in order to accomplish
external bus decoding. As part of the emulator configuration, the user can
indicate the desired SIM and RAM values by loading the EMSIM and EMRAM
copy registers. Once these register copies have been loaded, memory
resources (either emulation or target memory) can be accessed in the same
manner that the processor will access them when running target code. Note
that the default programming of the EMSIM and EMRAM registers is exactly
the same as the reset values of the SIM and RAM registers, as defined by the
Motorola 6833x User Manuals.
In addition to providing the programming knowledge for the external bus
decoder, the EMSIM and EMRAM registers provide a very helpful feature.
Suppose the emulator user wants to load target memory RAM which has been
implemented to be accessible via processor chip selects. In order to access
this memory, the processor SIM registers must typically be changed from the
reset default values. This can be done by individually modifying each SIM
register or by running some processor initialization code. If the EMSIM
registers hold the desired values, it can also be done by simply transferring
the EMSIM registers into the SIM registers. As a convenience to the user,
this transfer is performed automatically each time the monitor is entered
from emulation reset. This is the only time that this transfer is performed
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