Re: A89: Re: FYI: added info to J89hw.txt


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Re: A89: Re: FYI: added info to J89hw.txt




Johan wrote:
> The bus activity when executing the code fragment above is:
> 
>    fetch NOP instruction
>    fetch NOP instruction
>    fetch NOP instruction
>    fetch MOVE #xxx,SR instruction
> -> fetch immediate data to MOVE instruction ("$2700")
> -> fetch MOVE D0,(A0) instruction
> -> fetch instruction following the MOVE
> -> write to $1Cxxxx (execute the MOVE instruction)
>    fetch next instruction etc...
> 
> The four lines with "->" are the important ones. As you can see, the NOPs
> are not necessary! Note that the write is "delayed" -- the 68000 has a
> one-word prefetch queue. (Who said you never learn anything useful at
> school?!? :-) )

Smart :) When you say it, I learn't that in school too, but it didn't occour to
me. Easy to forget that prefetch thing. I guess we took the same course, or
almost at least.
obviously, the coders at TI should take that course too ;)

//Olle



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