PPC 405 in Virtex 2 Pro 30-Turning off "Critical-word first" loads

From: Nju Njoroge (njoroge_at_stanford.edu)
Date: 02/18/05

Date: Thu, 17 Feb 2005 15:06:30 -0800


I'm trying to disable "Critical-word first" loads for cache loads. That
is, when the cache is performing a cache refill, it first loads the target
data from memory, then loads the remaining words in the cacheline from
memory--all as part of a burst transaction. I'm looking for a way to
disable this type of cache fill. Instead, I would like the cache to load
the cacheline starting from the base address of the cacheline. Any one
tried this before? The reference guide claims that the PLB memory
controller can send back the data in the order it desires
(http://www.xilinx.com/bvdocs/userguides/ppc_ref_guide.pdf, page 146).
However, in reality, when my PLB slave pcore sends back the data in order
of ascending addresses, the processor assumes that I sent it back the
target data first, so it uses the wrong word.