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Revision as of 03:05, 7 March 2007 (view source) osdev>Jhawthorn No edit summary		Latest revision as of 04:30, 9 June 2024 (view source) Xtex (talk \| contribs) m (Bot: Replace deprecated source tag with syntaxhighlight)
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Line 1: Identity Paging, Identity Mapped ~~paging~~Paging and 1:1 ~~paging~~Paging are terms often used on the forum to describe a design choice where a portion of [virtual addresses~~\|Physical, Virtual, Paging, help?!?]~~ are mapped to physical addresses that have the same value. This means that if paging is enabled with identity paging, <tt>0xb8000</tt> '''is''' <tt>0xb8000</tt>, as long as that area is identity mapped.▼ ~~{{Convert}}~~ ==Advantages== ▲Identity Paging, Identity Mapped paging and 1:1 paging are terms often used on the forum to describe a design choice where a portion of [virtual addresses\|Physical, Virtual, Paging, help?!?] are mapped to physical addresses that have the same value. When switching to paged protected mode, your 1:1 mapping region doesn't care of whether paging is enabled or disabled. Placing your switching code and important data such as the core page directory and a few system page tables in this region gives you an easier way to set up paging without headaches.▼ ==Example== ~~For~~Let's ~~instance~~say you ~~may~~ decide to use ~~IdentityPaging~~Identity Paging in the lowest 1MB,. inIn ~~which~~this case vaddr =<tt>00000000</tt>..<tt>00000fff=</tt> are mapped to frame #00000, vaddr =<tt>00001000</tt>..<tt>00001fff=</tt> are mapped to frame #00001, and so on. (vaddr =<tt>000ff000</tt>..<tt>000fffff=</tt> are mapped to frame #000ff) You can easily do this with a loop filling the page table: <syntaxhighlight lang="c"> ~~<verbatim>~~ void idpaging(~~dword~~uint32_t first_pte, vaddr from, int size) { from = from & 0xfffff000; // discard bits we don't want▼ { for(; size>0; from += 4096, size -= 4096, first_pte++) {▼ ▲ from = from & 0xfffff000; // discard bits we don't want first_pte = from \| 1; // mark page present.▼ ▲ for(;size;from+=4096,first_pte++) { } ▲ first_pte=from\|1; // mark page present. } </syntaxhighlight> } ~~</verbatim>~~ ==See Also== ~~!What's the advantage of 1:1 paging~~ ===Articles=== [[Memory Management]] * [[Paging]] [[Category:Memory management]] ▲When switching to paged protected mode, your 1:1 mapping region doesn't care of whether paging is enabled or disabled. Placing your switching code and important data such as the core page directory and a few system page tables in this region gives you an easier way to set up paging without headaches.