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

[Hesham Moustafa]

Eight: 4 for data and 4 for instructions. BAT areas can not overlap.

Hesham
On Jun 22, 2013 12:39 AM, "Chris Johns" <chrisj at rtems.org> wrote:

> Hesham Moustafa wrote:
>
>> Hi there,
>>
>> I am working on providing memory protection for many targets/BSPs that
>> RTEMS support through a library called libmm. Previous MMU projects
>> depended on "Pages" to provide memory protection. I was thinking of
>> using BATs for extending libmm for PowerPC targets. The following are
>> some characteristics for BAT (Block Address Translation) and Pages for
>> PowerPC/mpc6xx.
>>
>> For BATs :
>> - BAT sizes varies from 128KB up to 256 MB.
>> - 8 pairs of register to describe blocks of memory: 4 for data blocks
>> and 4 for instructions blocks.
>> - It's faster than Page translation.
>> - Simple.
>>
>> For Pages :
>> - Page sizes begins from 4KB.
>> - Hash function are used for Page tables search and insert.
>> - Slower than BAT.
>> - Complex Code and cost much time when dynamically change attributes.
>>
>> The current code for libmm/PowerPC is using Pages. Do you think it's
>> suitable to implement libmm to use BAT also ?
>>
>> Waiting for your feed back.
>>
>>
> How many BAT areas can you have ?
>
> Chris
>
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