HP MC68360 User Manual page 466

Chapter 13: Concepts of the EMSIM and EMRAM
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 32-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 32-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 32-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 32-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 68360 User Manuals.
In addition to providing the programming knowledge for the external bus decoder,
the EMSIM and EMRAM registers provide another helpful feature. Suppose you
want to load target memory RAM that 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, you can access
this memory by simply transferring the EMSIM registers into the SIM registers.
As a convenience, this transfer is performed automatically each time the monitor is
entered from emulation reset. This is the only time that this transfer is performed
automatically; you can manually transfer the EMSIM to the SIM or the SIM to the
EMSIM or display their differences at any time.
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