OSDev.org

Code: Select all

// Map a region of virtual addresses to somewhere in RAM (allocate a region of virtual memory).
// Assumes length is a multiple of 4K.
bool allocateVirtualRegion(uintptr_t begin, size_t length)
{
  // For every page...
  for (uintptr_t page = begin; page < begin+length; page += PAGE_SIZE)
  {
    physical_uintptr_t physical = getPhysicalPage(); // This calls the physical memory allocator, and asks for it to allocate one page.
    mapPage(page, physical); // This tells the virtual memory manager to map the virtual page "page" to the physical page "physical".
  }
  return true;
}

Code: Select all

Virtual Memory Allocator is not based on Physical Memory Allocator

Code: Select all

unit pmm;

interface

var
  FrameStack: PLongWord;
  FrameStackTop: LongWord;
  NumOfFrames: LongWord;

function AllocFrame: PLongWord;
procedure FreeFrame(var Addr: PLongWord);
function FreeFramesLeft: LongWord;
procedure InstallPMM(FrameCount: LongWord);

implementation

uses
  console,paging;

function AllocFrame: PLongWord;
begin
  if FrameStackTop<NumOfFrames then begin
    AllocFrame:=PLongWord(FrameStack[FrameStackTop]);
    Inc(FrameStackTop);
  end else begin
    { Well, a swap should be tried before showing this }
    SetTextColor(scBlack,scRed);
    WriteString('Out of physical memory!');
    SetTextColor(scBlack,scLightGrey);
    WriteChar(#10);
    AllocFrame:=nil;
  end;
end;

procedure FreeFrame(var Addr: PLongWord);
begin
  Dec(FrameStackTop);
  FrameStack[FrameStackTop]:=PtrUInt(Addr);
  Addr:=nil;
end;

function FreeFramesLeft: LongWord;
begin
  FreeFramesLeft:=NumOfFrames-FrameStackTop+1;
end;

procedure InstallPMM(FrameCount: LongWord);
var
  i: LongWord;
begin
  WriteString('Installing Physical MM...'#9);
  FrameStack:=PageTable[768]+1024;
  FrameStackTop:=0;
  NumOfFrames:=FrameCount;
  for i:=0 to NumOfFrames-1 do
    FrameStack[i]:=PtrUInt(@FrameStack[NumOfFrames-1])+PageSize+(i*PageSize);
  WriteStrLn('[ OK ]');
end;

end.

Code: Select all

repeat
  WriteStrLn(HexStr(PtrUInt(p),8)+' = '+HexStr(p^,8));
  p:=AllocFrame;
until not Assigned(p);