#: 13963 S1/General Interest
    12-Jan-92  08:24:47
Sb: #Fast 6809 emulator!
Fm: John Semler 70324,633
To: Kevin Darling 76703,4227 (X)

Kevin,

    I got my "fast mode" emulator running!  Here is some CPU timing results
when running the floating point intensive program "ALMANAC":

 Machine    Time (seconds)    Comments

 CoCo3         55 secs
 CoCo2        110 secs       CoCo3 times * 2 (estimated)
 MacIIcx      132 secs       Running the "Fast mode" emulator

Programs are preloaded when performing the timing studies (just to be fair to
the CoCo3!).  The "fast" mode of emulation requires that the program does not
generate and execute new code.  As you can see, I almost break even with the
CoCo2. If it were not for the half carry flag calculations, the emulator would
probably match or beat the CoCo2.

This "fast mode" emulator is a little bit different from what I have previously
envisioned .  Each IOC quad word is composed of a jump vector (4 bytes) for
executing 6809 primitives and a variation word (4 bytes). Total IOC memory
requirement is 65536*8 bytes (In addition to 65536 bytes of "real" memory).
Instructions are incrementally compiled into IOC when first encountered.  Under
the "slow mode" IOC that becomes dirty will also be recompiled if executed.

Size of the emulator:

    Total 68020 instructions:      150,980 bytes
    Total data space requirement:  593,324 bytes

This emulator developement work was made much easier by the fact that I
developed a user state OS9/6809 debugger that operates like the OS9/68K
version.  I set up this debugger on both systems so that I can verify the
proper executions of millions of instructions!  The last bug I smashed didn't
occur until about 1.5 million instructions into the program "ALMANAC"!  This
debugger will have nearly everything that the OS9/68K version has including
symbolic debugging.

John

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