2008年最后一帖——了结MMU和cache（顺便纠正以前的错误）

这两天，重新看了MMU和cache，对它有了一点了解，现在再把疑问放到论坛上来，希望大家帮忙（前几天参与押宝，现在分数还没有回来，没有分发帖了，以后有分再补回吧，sorry）
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我看了的ADS bootloader部分，发现一个很奇怪的问题，它居然只是对一级页表做了配置，并且把虚拟内存和物理内存映射成相等
不知道为什么会这样。这不是多此一举吗？
看如下代码（三星提供）

/************************************************ 
  NAME    : MMU.C
  DESC	  :
  Revision: 2002.2.28 ver 0.0
 ************************************************/

#include "def.h"
#include "option.h"
#include "2440addr.h"
#include "2440lib.h"
#include "2440slib.h"
#include "mmu.h"

// 1) Only the section table is used. 
// 2) The cachable/non-cachable area can be changed by MMT_DEFAULT value.
//    The section size is 1MB.

 

void MMU_Init(void)
{
    int i,j;
    //========================== IMPORTANT NOTE =========================
    //The current stack and code area can't be re-mapped in this routine.
    //If you want memory map mapped freely, your own sophiscated MMU
    //initialization code is needed.
    //===================================================================

    MMU_DisableDCache();
    MMU_DisableICache();

    //If write-back is used,the DCache should be cleared.
    for(i=0;i<64;i++)
    	for(j=0;j<8;j++)
    	    MMU_CleanInvalidateDCacheIndex((i<<26)|(j<<5));
    MMU_InvalidateICache();
    
    #if 0
    //To complete MMU_Init() fast, Icache may be turned on here.
    MMU_EnableICache(); 
    #endif
    
    MMU_DisableMMU();
    MMU_InvalidateTLB();

    //MMU_SetMTT(int vaddrStart,int vaddrEnd,int paddrStart,int attr)
    MMU_SetMTT(0x00000000,0x07f00000,0x00000000,RW_CNB);  //bank0
    MMU_SetMTT(0x08000000,0x0ff00000,0x08000000,RW_CNB);  //bank1
    MMU_SetMTT(0x10000000,0x17f00000,0x10000000,RW_NCNB); //bank2
    MMU_SetMTT(0x18000000,0x1ff00000,0x18000000,RW_NCNB); //bank3
    //MMU_SetMTT(0x20000000,0x27f00000,0x20000000,RW_CB); //bank4
    MMU_SetMTT(0x20000000,0x27f00000,0x20000000,RW_CNB); //bank4 for STRATA Flash
    MMU_SetMTT(0x28000000,0x2ff00000,0x28000000,RW_NCNB); //bank5
    MMU_SetMTT(0x30000000,0x30f00000,0x30000000,RW_CB);	  //bank6-1
    MMU_SetMTT(0x31000000,0x33e00000,0x31000000,RW_NCNB); //bank6-2
    MMU_SetMTT(0x33f00000,0x33f00000,0x33f00000,RW_CB);   //bank6-3
    MMU_SetMTT(0x38000000,0x3ff00000,0x38000000,RW_NCNB); //bank7
    
    MMU_SetMTT(0x40000000,0x47f00000,0x40000000,RW_NCNB); //SFR
    MMU_SetMTT(0x48000000,0x5af00000,0x48000000,RW_NCNB); //SFR
    MMU_SetMTT(0x5b000000,0x5b000000,0x5b000000,RW_NCNB); //SFR
    MMU_SetMTT(0x5b100000,0xfff00000,0x5b100000,RW_FAULT);//not used

    
    MMU_SetTTBase(_MMUTT_STARTADDRESS);
    MMU_SetDomain(0x55555550|DOMAIN1_ATTR|DOMAIN0_ATTR); 
    	//DOMAIN1: no_access, DOMAIN0,2~15=client(AP is checked)
    MMU_SetProcessId(0x0);
    MMU_EnableAlignFault();
    	
    MMU_EnableMMU();
    MMU_EnableICache();
    MMU_EnableDCache(); //DCache should be turned on after MMU is turned on.
}    


// attr=RW_CB,RW_CNB,RW_NCNB,RW_FAULT
void ChangeRomCacheStatus(int attr)
{
    int i,j;
    MMU_DisableDCache();
    MMU_DisableICache();
    //If write-back is used,the DCache should be cleared.
    for(i=0;i<64;i++)
    	for(j=0;j<8;j++)
    	    MMU_CleanInvalidateDCacheIndex((i<<26)|(j<<5));
    MMU_InvalidateICache();
    MMU_DisableMMU();
    MMU_InvalidateTLB();
    MMU_SetMTT(0x00000000,0x07f00000,0x00000000,attr);	//bank0
    MMU_SetMTT(0x08000000,0x0ff00000,0x08000000,attr);	//bank1
    MMU_EnableMMU();
    MMU_EnableICache();
    MMU_EnableDCache();
}    
    

void MMU_SetMTT(int vaddrStart,int vaddrEnd,int paddrStart,int attr)
{
    volatile U32 *pTT;
    volatile int i,nSec;
    pTT=(U32 *)_MMUTT_STARTADDRESS+(vaddrStart>>20);
    nSec=(vaddrEnd>>20)-(vaddrStart>>20);
    for(i=0;i<=nSec;i++)*pTT++=attr |(((paddrStart>>20)+i)<<20);
}

但是在eboot中使用 的映射就是使用OEMAddresstable来初始化页表，这是wince真正的虚实映射
说道这里OEMAddresstable的虚拟起始地址0x80000000是wince规定的还是本来ARM决定的？
我觉得这个虚拟地址是可以改变的，所以才会可以把物理地址和虚拟地址映射成相等的？
各位有什么看法，多多交流啊。