Hello Ron, These are the excellent points! I did not know/had no clue this myself. It is a good remark, I would not know to search/discover for this!?
The other good point is that CAR/NEM was developed by student in INTEL, doing his internship (which I always asked myself why such major things were developed by students???)?! ;-) I have one question here: > Basically, in the classic car we got in 2005, the steps on x86 are: > enable cache *> do references to set tags* > disable cache (really!) > then cache as ram works. I am interested how this is implemented, in *RED* (if you can point to some Coreboot implementation)? Hello Qureshi, Any quick points about *do reference to set tags *(implementation wise)? Thank you all, Zoran On Tue, Aug 9, 2016 at 6:44 PM, ron minnich <rminn...@gmail.com> wrote: > I have not read this thread closely and maybe I'm telling you something > you know. But I want to warn you about CD. I know it is named 'cache > disabled' > but that's not quite what it means. > > I'm trying and failing to find the original slide deck from the UNM grad > student (and intel employee) who first implemented our cache as ram in > 2005. His point to me was that CD doesn't *really* mean cache hardware is > disabled, just that it changes cache hardware behavior such that refills > from memory are disabled. If there are valid tags in the cache then loads > that hit those tags will work. So the task for CAR on x86 is to create > valid tags, then set CD. His point was the breakthrough for me on > understanding CAR on x86. Ollie Lo and I had been stuck on this point for a > while, we kept thinking we could not set CD and have CAR work; in fact, > setting CD is part of ensuring CAR works. The Intel employee's point was > "you have to read between the lines in section III". > > you can > git grep DO.NOT.INVALIDATE > for a few comments on this and it may help. > > Basically, in the classic car we got in 2005, the steps on x86 are: > enable cache > do references to set tags > disable cache (really!) > then cache as ram works. > > Things have changed on some CPUs since then and we now even have > chipset-dependent x86 CAR code but I suspect the basic idea remains the > same on x86. > > You may already know this, just wanted to make sure. > > ron > > -- > coreboot mailing list: coreboot@coreboot.org > https://www.coreboot.org/mailman/listinfo/coreboot >
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