HP 64783A, User Manual

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Using an FPU with an MC68EC040 or MC68LC040
Target System
The MC68EC040 and MC68LC040 processors do not have an on-chip FPU. When
floating-point functionality is required, all floating-point operations must be
implemented in software using integer instructions. Language systems usually
provide a floating-point software library for this purpose.
The HP 64783A/B emulator uses an MC68040 processor with an on-chip FPU.
Because there is no way to disable the FPU, floating-point operations may execute
differently, depending on the language system used. If your language system
generates calls directly to the floating-point software library and does not emit any
opcodes for floating-point instructions, then there should be no difference in
floating-point operations whether you are using the emulator or the
MC68EC040/LC040 processor plugged into your target system.
If your language system emits opcodes for floating-point instructions and relies on
an F-Line exception handler to call the floating-point software library when the
instruction is executed, then your target system will operate differently when the
emulator is plugged in. When using the emulator, most floating-point instructions
will be executed on the FPU in hardware instead of generating an F-Line exception
and allowing the floating-point operations to be implemented in software. For this
scenario, the following three points should be taken into consideration:
•
Floating-point software libraries cannot be tested while the emulator is plugged
in. Floating-point instructions are always executed on-chip, not by your
floating-point libraries. This will definitely cause a problem for anyone trying
to develop floating-point software libraries.
•
Target programs containing FPU instructions will run faster when the emulator
is plugged into the target system because they are executed in the hardware of
the MC68040 instead of by the floating-point software libraries, as they will be
when the MC68EC040/LC040 processor is plugged in. This will cause
performance measurements to show much better results when using the
emulator than you will actually obtain when you use the MC68EC040/LC040
processor.
•
If you are unaware that your language tools use floating-point instructions (and
you do not actively provide floating-point libraries and F-Line exception
handling), you may find that your target system does not work when you
unplug the emulator and plug in your MC68EC040/LC040 target processor.
Chapter 4: Using the Emulator
Using an FPU with an MC68EC040 or MC68LC040 Target System
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