Hardware Reference
In-Depth Information
FIGURE C.57
Scoreboard tables just before the
DIV.D
goes to write result
.
ADD.D
was able to complete as soon as
DIV.D
passed through read operands and
got a copy of F6. Only the
DIV.D
remains to finish.
Now we can see how the scoreboard works in detail by looking at what has
to happen for the scoreboard to allow each instruction to proceed.
Figure C.58
shows what the scoreboard requires for each instruction to advance and the
bookkeeping action necessary when the instruction does advance. The score-
board records operand specifier information, such as register numbers. For ex-
ample, we must record the source registers when an instruction is issued. Be-
cause we refer to the contents of a register as
Regs[D]
, where
D
is a register name,
there is no ambiguity. For example,
Fj[FU]
←
S1
causes the register
name
S1
to be
placed in
Fj[FU]
, rather than the
contents
of register
S1
.
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