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

[Hesham Moustafa]

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.

Thanks,
Hesham
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