/// <summary>
/// Converts the virtual address into a physical address, then returns the address.
/// </summary>
/// <param name="address">The address.</param>
/// <returns>Returns the physical address</returns>
public string Read(int address)
{
var virtualAddress = new VirtualAddress(address);
if (tlb != null)
{
var pa = DoesEntryExist(virtualAddress);
if (pa != -1)
{
return("h " + pa);
}
}
var pageTable = GetPageTable(virtualAddress.segment);
if (pageTable == -1 || pageTable == 0)
{
return(pageTable.ToString());
}
var page = GetPage(pageTable + virtualAddress.page);
if (page == -1 || page == 0)
{
return(page.ToString());
}
if (tlb != null)
{
InsertEntry(virtualAddress);
}
return(tlb != null ? "m " + (page + virtualAddress.word) : (page + virtualAddress.word).ToString());
}
/// <summary>
/// Converts the virtual address into a phsyical address. If the segment table's value is
/// 0, then create a new page table. Consequently this will then have 0 for the page table,
/// and a new page needs to be created.
/// </summary>
/// <param name="address">The address.</param>
/// <returns>Returns the physical address</returns>
public string Write(int address)
{
var virtualAddress = new VirtualAddress(address);
if (tlb != null)
{
var pa = DoesEntryExist(virtualAddress);
if (pa != -1)
{
return("h " + pa);
}
}
var pageTable = GetPageTable(virtualAddress.segment);
if (pageTable == -1)
{
return(pageTable.ToString());
}
// Create page table
if (pageTable == 0)
{
var frame = GetFreePageTable();
EmptyFrame(frame);
pageTable = frame * FrameSize;
SetSegmentToPageTable(virtualAddress.segment, pageTable);
}
var page = GetPage(pageTable + virtualAddress.page);
if (page == -1)
{
return(page.ToString());
}
// Create page
if (page == 0)
{
var frame = GetFreeFrame();
EmptyFrame(frame);
page = frame * FrameSize;
SetPageToPageTable(pageTable + virtualAddress.page, page);
}
if (tlb != null)
{
InsertEntry(virtualAddress);
}
return(tlb != null ? "m " + (page + virtualAddress.word) : (page + virtualAddress.word).ToString());
}
/// <summary>
/// Inserts the tlb entry if it does not exist. If the entry exists, return
/// the frame number of the entry. Otherwise, return -1;
/// </summary>
/// <param name="page">The page.</param>
/// <param name="frame">The frame.</param>
/// <returns></returns>
private void InsertEntry(VirtualAddress va)
{
// Entry was not found, so replace the least recently used entry
foreach (var entry in tlb)
{
if (entry.priority == 0)
{
entry.priority = 3;
entry.sp = va.sp;
entry.f = physicalMemory[physicalMemory[va.segment] + va.page];
}
else
{
entry.priority -= 1;
}
}
}
private int DoesEntryExist(VirtualAddress va)
{
// search TLB for entry, then update it's priority and return PA
for (var i = 0; i < tlb.Count; i++)
{
if (tlb[i].sp == va.sp)
{
foreach (var entry in tlb)
{
if (entry.priority > tlb[i].priority)
{
entry.priority -= 1;
}
}
tlb[i].priority = 3;
return(tlb[i].f + va.word);
}
}
return(-1);
}
