#include	"u.h"
#include	"lib.h"
#include	"mem.h"
#include	"dat.h"
#include	"fns.h"
#include	"io.h"
#include	"ureg.h"

#define	DATASEGM(p) 	{ 0xFFFF, SEGG|SEGB|(0xF<<16)|SEGP|SEGPL(p)|SEGDATA|SEGW }
#define	EXECSEGM(p) 	{ 0xFFFF, SEGG|SEGD|(0xF<<16)|SEGP|SEGPL(p)|SEGEXEC|SEGR }
#define	TSSSEGM(b,p)	{ ((b)<<16)|sizeof(Tss),\
			  ((b)&0xFF000000)|(((b)>>16)&0xFF)|SEGTSS|SEGPL(p)|SEGP }

Segdesc gdt[6] =
{
[NULLSEG]	{ 0, 0},		/* null descriptor */
[KDSEG]		DATASEGM(0),		/* kernel data/stack */
[KESEG]		EXECSEGM(0),		/* kernel code */
[UDSEG]		DATASEGM(3),		/* user data/stack */
[UESEG]		EXECSEGM(3),		/* user code */
[TSSSEG]	TSSSEGM(0,0),		/* tss segment */
};

#define PDX(va)		((((ulong)(va))>>22) & 0x03FF)
#define PTX(va)		((((ulong)(va))>>12) & 0x03FF)

static void
taskswitch(ulong pagetbl, ulong stack)
{
	Tss *tss;

	tss = m->tss;
	tss->ss0 = KDSEL;
	tss->esp0 = stack;
	tss->ss1 = KDSEL;
	tss->esp1 = stack;
	tss->ss2 = KDSEL;
	tss->esp2 = stack;
	tss->cr3 = pagetbl;
	putcr3(pagetbl);
}

void
mmuinit(void)
{
	ulong x;
	ushort ptr[3];

	m->tss = malloc(sizeof(Tss));
	// this is redundant  memset(m->tss, 0, sizeof(Tss));

	memmove(m->gdt, gdt, sizeof(m->gdt));
	x = (ulong)m->tss;
	m->gdt[TSSSEG].d0 = (x<<16)|sizeof(Tss);
	m->gdt[TSSSEG].d1 = (x&0xFF000000)|((x>>16)&0xFF)|SEGTSS|SEGPL(0)|SEGP;

	ptr[0] = sizeof(m->gdt);
	x = (ulong)m->gdt;
	ptr[1] = x & 0xFFFF;
	ptr[2] = (x>>16) & 0xFFFF;
	lgdt(ptr);

	ptr[0] = sizeof(Segdesc)*256;
	x = IDTADDR;
	ptr[1] = x & 0xFFFF;
	ptr[2] = (x>>16) & 0xFFFF;
	lidt(ptr);

	taskswitch(PADDR(m->pdb),  (ulong)m + BY2PG);
	ltr(TSSSEL);
}