On Thu, 21 Feb 2002, Atsushi Nemoto wrote:
> TX39 satisfy this on uncached load/store. "sync" does not flush a
> write buffer, but any uncached load are executed AFTER completion of
> pending uncached store. On combination of cached and uncached
> operation, TX39 does not satisfy this order.
With respect to cache refills (what is already cached is irrelevant,
obviously, as read accesse to it don't appear externally), "32-bit RISC
Microprocessor TX39 Family Core Architecture User's Manual" seems to
contradict. In the description of the "sync" instruction it states:
"Interlocks the pipeline until the load, store or data cache refill
operation of the previous instruction is completed. The R3900 Processor
Core can continue processing instructions following a load instruction
even if a cache refill is caused by the load instruction or a load is made
from a noncacheable area. Executing a SYNC instruction interlocks
subsequent instructions until the SYNC instruction execution is completed.
This ensures that the instructions following a load instruction are
executed in the proper sequence."
It's clear "sync" is strong on the TX39, stronger then required by MIPS
> TX39 has a function called "non-blocking load". This function is
> described on chapter 4.4 of TX39/H2 manual. "sync" operation is
> meaningful with this function.
Chapter 4.3 ("") of the quoted manual. The statement I quoted assures
indeed (modulo errata, which hopefully don't exist here).
> Chapter 4.9.4 in TX39/H2 Japanese manual describes write buffer. But
> I could not find it in the English manual...
The write buffer is described in the part about "TMPR3901F" (it appears
two manuals are concatenated in a single file), chapter 2.3 ("Bus
Interface Unit (Bus Controller / Write Buffer)"). It looks like a "bc0f"
loop is needed for mb(). The only difference comparing to R2020/R3220 is
only a single "nop" is needed after a write for the coprocessor status to
become valid, it would seem. It's not documented explicitly but the
supplied example code suggests so.
The document I'm referring to is available at:
+ Maciej W. Rozycki, Technical University of Gdansk, Poland +
+ e-mail: firstname.lastname@example.org, PGP key available +