🚀 go-pugleaf

In article <4126@altos86.Altos.COM> rcollins@altos86.UUCP (Robert Collins) writes:
>Just a friendly note in case you don't know much about '386's...But the
>SX and DX have the same size prefetch queue.  This can be confirmed by
>simply looking in the SX and DX hardware reference manuals (respectively)
>and verify that both have 16-byte prefetch queues.  So code that checks
>the length of the prefetch queue isn't going to determine anything...
>except the length of the prefetch queue.

Somebody with a manual should probably double-check this assertion.
I do not have a manual any more, but my recollection is that both processors
have 4-deep prefetch queues.. that is, each can prefetch up to 4 machine words.

On a DX, a machine word is 32 bits, whereas on an SX it is 16 bits (for the
BIU, that is).  Thus, a DX has a 16-byte prefetch queue, and an SX has only 8.

The posted code (I missed it) probably failed to properly preload the prefetch
queue.  To do this, one must cleverly code a loop which is 12-bytes in length,
and which executes twice in succession, modifying itself the second 
time around (but not the first time).  This is necessary to overcome problems
with bus bandwidtch, which might otherwise affect this test.

The actual coding of such a beastie is left as an exercise for The Reader.
-- 
 ___Mark S. Lord__________________________________________
| ..uunet!bnrgate!mlord%bmerh724 | Climb Free Or Die (NH) |
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