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#include <paging.h>

unsigned long page_directory[1024] __attribute__ ((aligned (4096)));
unsigned long page_table[1024] __attribute__ ((aligned (4096)));

void paging_install() {
   int i = 0;
   unsigned long address=0;

   page_directory[0] = address;
   page_directory[0] = page_directory[0] | PG_PRESENT | PG_READWRITE | !PG_US | PG_SIZE;
   
   for(i=1; i<1024; i++) {
      page_directory[i] = 0 | !PG_PRESENT;
   }
   
   write_cr3(page_directory);
   write_cr4(read_cr4() | CR4_PSE_ENABLE );
   write_cr0(read_cr0() | 0x80000000 );
}

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// Page Attributes

#define PG_PRESENT 1   // 0 = not present, 1 = present
#define PG_READWRITE 2 // 0 = read-only, 1 = read-write
#define PG_US 4   // 0 = supervisor, 1 = user
#define PG_PWT 8   // Page write-through 0 = disabled, 1 = enabled
#define PG_PCD 16   // Page cache disable 0 = cached, 1 = not cached
#define PG_ACCESSED 32 // 0 = not accessed, 1 = accessed


#define PG_DIRTY 64 // 0 = not written to, 1 = written to  For page table
#define PGDT_SIZE 64 // For Page Directory table, should always be set to 0

#define PG_SIZE 128 // 0 = 4kbytes page, 1 = 4 mbyte page
// PG_PAT 0x256 ; don't want to support this yet.
/*
PG_GLOBAL if set, will not get invalidated in the TLB table. 
In order to work, the PGE flag in CR4 needs to be set
*/
#define PG_GLOBAL 512

// Bits 9,10,11 are available to software
// If PG_PRESENT is clear, bits 1 to 31 are available to software.

extern void paging_install();

#define CR4_PSE_ENABLE 16   // Page size extension