/*
 * Copyright 1993,1994,1995 Emin Gun Sirer
 * MIPSI - Mips Instruction Set Simulator.
 */
#include <stdio.h>
#include "config.h"
#include "main.h"
#include "mem.h"
#include "tlb.h"
#include "mt_os.h"
#include <assert.h>

#define TLB_SIZE   64
#define TLB_MASK   (TLB_SIZE-1) 

typedef struct tlb_elt {
    unsigned long vpage;
    unsigned long ppage;
    unsigned flags;
} tlb_elt;

tlb_elt TLB[TLB_SIZE];

void tlb_flush() {
    int i;
    for (i = 0; i < TLB_SIZE; i++) {
        TLB[i].vpage = INVALID;
    }
}

void tlb_invalidate (unsigned long vpage)
{
  int i;
  for (i = 0; i < TLB_SIZE; i++) {
    if (TLB[i].vpage == vpage) {
      TLB[i].vpage = INVALID;
    }
  }
}

unsigned long tlb_translate(unsigned long vaddr,c_rw rw) {
    unsigned long offset,paddr,vpage,ppage;
    unsigned long index;

    /* figure out the offset and the page */
    offset = GET_OFFSET(vaddr);
    vpage  = GET_PAGE(vaddr);
    
    /* figure out the table index */
    index = vpage & TLB_MASK;

    if (TLB[index].vpage == vpage) { /* check the tag */
        ppage = TLB[index].ppage;
    } else {
        return INVALID;
    }

    /* if attempt to write to a protected page */
    if ( (TLB[index].flags & TLB_WRITE_PROTECT) && (rw == C_WRITE)) {

        /* fault */
        unsigned long V0,A0,A1,A2,A3,RES;
	unsigned long vpage, flags;


	/* setup for a trap ---save the registers */
	V0 = R[REG_V0];  A0 = R[REG_A0]; A1 = R[REG_A1]; A2 = R[REG_A2];
	A3 = R[REG_A3];  RES = R[REG_RES];
	/* put in the trap number */
	R[REG_V0]  = MT_ENTRY;    /* to get an MT-OS call */
	R[REG_A0]  = MT_TLB_WRITE_FAULT; /* to pick the TLB fault */
	
	/* compute vpage */
	vpage = GET_PAGE(vaddr);
	
	/* put in the virtual page */
	R[REG_A1]  = vpage;
	
	dosyscall();   /* perform the trap */
	
	/* get the resulting flags */
	TLB[index].flags = R[REG_RES];

 	/* restore the registers */
	R[REG_V0] = V0;  R[REG_A0] = A0; R[REG_A1] = A1; R[REG_A2] = A2;
	R[REG_A3] = A3;  R[REG_RES] = RES;
    }

    /* put together the physical page and the offset */
    paddr = (ppage << PAGESHIFT) | offset;
    if (paddr & 3) {
       index = 5;
     }

    return paddr;
}


void set_tlb_ppage(unsigned long vpage, PTE ptentry) {
    unsigned long index;
    index = vpage & TLB_MASK;
    TLB[index].ppage = TLB_GETPAGE(ptentry);
    TLB[index].flags = TLB_GETFLAGS(ptentry);
    TLB[index].vpage = vpage;
}

void set_tlb_flags(unsigned long vpage, unsigned flags) {
    unsigned long index;

    index = vpage & TLB_MASK;
    assert(vpage == TLB[index].vpage);
    TLB[index].flags = flags;

}