[GSoC] BAT vs Pages on PowerPC [Please give a feedback]

Chris Johns chrisj at rtems.org
Sun Jun 23 10:55:25 UTC 2013

Thomas Doerfler wrote:
> Chris,
> Am 23.06.2013 03:46, schrieb Chris Johns:
>> Thomas Dörfler wrote:
>>> Note that the pages usually only cover 4K of
>>> memory, and the "translation lookaside buffer" (TLB) only maintains the
>>> last 16-64 used pages,
>> The ARM which I am currently using and have handy seems to support 1MB,
>> 64K and 4K ranges depending on the TLB table level used. I would be
>> surprised if an entry was needed for each page in use.
> Classic PowerPC ist not that flexible. The 603(e) core, that is quite
> often used in PPC controllers, has a fixed page table entry size of 4K,
> so the number of TLB entries (the "page cache") will never cover the
> whole lot of pages for a suitable memory size.

Interesting and thanks. It is a difficult API to make because of these 
reasons. Hesham has some interesting challenges.

> So for this derivative (and many others) it's "Use (statically
> initialized) BATs or (dynamically reloaded) TLB entries".

Agreed. Is this worth adding to the API ?


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