/// <summary>
/// Initializes the GDT
/// </summary>
public static unsafe void Init()
{
// Allocate data
m_entries = new GDT_Entry[6];
m_ptr = new GDT_Pointer();
// Set GDT table pointer
m_ptr.Limit = (ushort)((6 * sizeof(GDT_Entry)) - 1);
fixed(GDT_Entry *ptr = m_entries)
{
m_ptr.BaseAddress = (uint)ptr;
}
// NULL segment
setEntry(0, 0, 0, 0, 0);
// Kernel code segment
setEntry(1, 0, 0xFFFFFFFF, (int)GDT_Data.ER | (int)GDTFlags.DescriptorCodeOrData | Privilege(0) | (int)GDTFlags.Present, (int)GDTFlags.Size32 | (int)GDTFlags.Granularity);
// Kernel data segment
setEntry(2, 0, 0xFFFFFFFF, (int)GDT_Data.RW | (int)GDTFlags.DescriptorCodeOrData | Privilege(0) | (int)GDTFlags.Present, (int)GDTFlags.Size32 | (int)GDTFlags.Granularity);
// User code segment
setEntry(3, 0, 0xFFFFFFFF, (int)GDT_Data.ER | (int)GDTFlags.DescriptorCodeOrData | Privilege(3) | (int)GDTFlags.Present, (int)GDTFlags.Size32 | (int)GDTFlags.Granularity);
// User data segment
setEntry(4, 0, 0xFFFFFFFF, (int)GDT_Data.RW | (int)GDTFlags.DescriptorCodeOrData | Privilege(3) | (int)GDTFlags.Present, (int)GDTFlags.Size32 | (int)GDTFlags.Granularity);
// TSS
TSS_Entry = (TSS *)Heap.Alloc(sizeof(TSS));
setTSS(5, TSS_Entry);
// Flush GDT
fixed(GDT_Pointer *ptr = &m_ptr)
{
flushGDT(ptr);
}
// Flush TSS
flushTSS();
}
/// <summary>
/// Writes a TSS entry into the GDT
/// </summary>
/// <param name="num">The index of the corresponding GDT entry</param>
/// <param name="tss">The TSS</param>
private static unsafe void setTSS(int num, TSS *tss)
{
// Base and limit
uint baseAddr = (uint)tss;
uint limit = (uint)(baseAddr + sizeof(TSS));
// Set TSS
// Kernel Data Selector = 0x10, Kernel Code Selector = 0x08
Memory.Memclear(tss, sizeof(TSS));
tss->SS0 = 0x10;
tss->IOMap = (ushort)sizeof(TSS);
tss->CS = 0x08;
tss->DS = 0x10;
tss->ES = 0x10;
tss->FS = 0x10;
tss->GS = 0x10;
tss->SS = 0x10;
// Add TSS descriptor to GDT
setEntry(num, baseAddr, limit, (int)GDT_Data.EA | Privilege(3) | (int)GDTFlags.Present, 0);
}
public static void Init()
{
//ExceptionMethods.ThePageFaultHandler = HandlePageFault;
ActiveQueue.Name = "Active Queue";
InactiveQueue.Name = "Inactive Queue";
//Load first process and first thread
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Setting current process...");
#endif
ProcessManager.CurrentProcess = (Process)ProcessManager.Processes[0];
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Setting current thread...");
#endif
ProcessManager.CurrentThread = (Thread)ProcessManager.CurrentProcess.Threads[0];
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Setting current thread state...");
#endif
ProcessManager.CurrentThread_State = ProcessManager.CurrentThread.State;
//Init TSS
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Getting TSS pointer...");
#endif
TSS *tss = GetTSSPointer();
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Setting esp0...");
#endif
tss->esp0 = (uint)ProcessManager.CurrentThread_State->KernelStackTop;
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Setting ss0...");
#endif
//Note: KM CS is loaded from IDT entry on ring 3 -> 0 switch
tss->ss0 = 0x10; //Kernel mode stack segment = KM Data segment (same for all processes)
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Setting cr3...");
#endif
tss->cr3 = VirtMem.x86.GetCR3();
//Load Task Register
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Loading TR...");
#endif
LoadTR();
//Enable timer
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Adding timer handler...");
#endif
/*Multiply by 1000000 to get from ms to ns*/
Hardware.Devices.Timer.Default.RegisterHandler(OnTimerInterrupt, /* MSFreq * 1000000 */ 5000000, true, null);
#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Enabling process switching...");
#endif
Interrupts.Interrupts.EnableProcessSwitching = true;
//#if SCHEDULER_TRACE
BasicConsole.WriteLine(" > Enabling scheduler...");
//#endif
UpdateCountdown = UpdatePeriod;
Initialised = true;
Enable();
}