On Fri, 15 Feb 2002, Dominic Sweetman wrote:
> That's only a problem if the CPU permitted reads to overtake buffered
> writes. [Early R3000 write buffers did that (with an address check to
> avoid the disaster of allowing a read to overtake a write to the same
> location).]
The R2020 and the R3220 write buffers that are used in older DECstations
seem to provide buffered values themselves if hit by a read. This way
they are completely safe for ordinary memory references and there is no
need to stall for a write-back completion for memory operations. At least
this is what DECstation specifications imply -- it seems hard to get to
original docs for the chips these days.
For I/O resources implying side effects a stall is needed, of course.
The way the chips work is not that uncommon -- e.g. Intel's i486 does
exactly the same.
--
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+--------------------------------------------------------------+
+ e-mail: macro@ds2.pg.gda.pl, PGP key available +
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