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 +
