paging.c

一个操作系统的源代码

/** paging.c                                  
 **
 ** Original Author: Kasper Verdich Lund                         
 ** Date: 10.30.99     
 ** 
 ** Description:
 **                                       
 ** Revision History: 
 ** First version     
 **
 ** 0.0.1 10.30.99 Kasper Verdich Lund - (no comments)
 **
 ** This program is free software, you can redistribute it and/or
 ** modify it under the terms of the GNU General Public License  
 ** as published by the Free Software Foundation; either version 
 ** 2 of the License, or (at your option) any later version.     
 **                                                              
 ** This program is distributed in the hope that it will be      
 ** useful, but WITHOUT ANY WARRANTY; without even the implied   
 ** warranty or MERCHANTABILITY or FITNESS FOR A PARTICULAR      
 ** PURPOSE.  See the GNU General Public License for more       
 ** details.                                                     
 **                                                              
 ** You should have received a copy of the GNU General Public    
 ** License along with this program; if not, write to the        
 ** Free Software Foundation, Inc., 59 Temple Place, Suite 330,  
 ** Boston, MA 02111-1307 USA                                    
 **                                                              
 *********************************************************Apostle OS**/

#include <paging.h>
#include <mem.h>
#include <string.h>
#include <types.h>

dword CR3;

void setupPaging(dword available)
{
  dword *PD, *PT;
  int i, tables = 0;

  CR3 = (dword) pmalloc();
  PD = (dword *) CR3;
  PT = NULL;

  /* do not map more than 256Mb of physical memory */
  if (available > 256*1024*1024)
    available = 256*1024*1024;
  for(i=0; i<(available >> 12); i++)
    {
      if ((i & 0x3FF) == 0) 
	{
	  PT = p2malloc();
	  tables++;
	  PD[i>>10] = (dword)PT + PAGE_PRESENT;
	  memset((void *)((dword)PT + PAGE_SIZE), 0, PAGE_SIZE);
	}
      PT[i & 0x3FF] = (i << 12) + PAGE_PRESENT;
    }
}

void enablePaging(void)
{
  dword CR0 = get_CR0();
  set_CR3(CR3);
  /* set most significant bit of CR0 */
  set_CR0(CR0 | 0x80000000); 
}