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Altera_Forum
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16 years ago

Linux with MMU on NEEK

Hi, all. I'm testing Linux MMU version, on my NEEK. http://www.nioswiki.com/linux It works fine and I can use "bash" shell. This is the evident proof that we are using the true 'fo...
Altera_Forum's avatar
Altera_Forum
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16 years ago

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Hmmm, AFAIR, the hardware manual states that with MMU, bit 31 is not use for cache enabling purpose, but that you need to create dedicated MMU pages for non-caching accesses (with the appropriate cacheable bit setting in the page descriptor). But of course nobody prevents you from defining all pages with the virtual address bit 31 set as non-cacheable. I have no idea how all this is done in the Kernel code.

-Michael

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OK, I found the manual (http://www.altera.com/literature/hb/nios2/n2cpu_nii51003.pdf), and you are right, bit 31 is not used that way. However, virtual addresses 0xe0000000 and above are are mapped for I/O, skipping the TLB and the cache. So the behavior of ioremap is correct.