/*
 * This file contains the scheduler.  It implements a basic task switching
 * routine, as well as the schedule() function.  The scheduler can be called
 * from anywhere, and will switch to the next task decided by the scheduler
 * rules.  If it cannot find a task to schedule, it just idles until one becomes
 * available.  This avoids the need for an idle task.
 */

#include <nucleus/panic.h>
#include <nucleus/task.h>

/* Read the EIP */
static uintptr_t
read_eip(void)
{
	uintptr_t eip;
	asm volatile("movl 4(%%ebp), %0" : "=r" (eip));
	return eip;
}

/* Switch to a task */
static void
switch_to_task(Task *task)
{
	uintptr_t esp, ebp, eip;
	asm volatile("mov %%esp, %0" : "=r" (esp));
	asm volatile("mov %%ebp, %0" : "=r" (ebp));
	eip = read_eip();
	if (eip == 0x10032004) /* Magic number */
		return;

	current->esp = esp;
	current->ebp = ebp;
	current->eip = eip;
	current = task;
	esp = current->esp;
	ebp = current->ebp;
	eip = current->eip;

	asm volatile (
		"cli;"
		"movl %0, %%ecx;"
		"movl %1, %%esp;"
		"movl %2, %%ebp;"
		"movl %3, %%cr3;"
		"movl $0x10032004, %%eax;"
		"sti;"
		"jmp *%%ecx"
		:: "g" (eip), "g" (esp), "g" (ebp), "g" (current->pageDir)
	);
}

/* Schedule the next task */
void
schedule(void)
{
	Task *task = current;
	if (!task->next)
		return;
	switch_to_task(task->next);
}