MMU相关指令学习（二）（主要是页表设置指令）

作者：wogoyixikexie@gliet

    本来打算在《MMU相关指令学习（一）（主要是页表设置指令）》搞定MMU指令问题的，但是这个实在是太长太多，太复杂了，现在就新开一文，就地解决！——刚好是第一百篇原创，值得纪念。

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Assembly code

; ——在OAL的startup.s有如下：
; add     r0, pc, #g_oalAddressTable - (. + 8)
;         bl      KernelStart
; ——以前真的没有仔细看过这些汇编，看过才能知道这个wince的流程到底是怎么回事。
; 这相当于一到OAL阶段就要重新初始化页表，MMU，cache使能控制等 其实是一级、二级页表都在这里设置的
; 在C:/WINCE500/PRIVATE/WINCEOS/COREOS/NK/KERNEL/ARM/armtrap.s有KernelStart，现在好好分析一下。
; ----------------------------------------------------------------------------------------
; KernelStart - kernel main entry point
;
;        The OEM layer will setup any platform or CPU specific configuration that is
; required for the kernel to have access to ROM and DRAM and jump here to start up
; the system. Any processor specific cache or MMU initialization should be completed.
; The MMU and caches should not enabled.
;
;        This routine will initialize the first-level page table based up the contents of
; the MemoryMap array and enable the MMU and caches.
;
; NOTE: Until the MMU is enabled, kernel symbolic addresses are not valid and must be
;        translated via the MemoryMap array to find the correct physical address.
;
;        Entry   (r0) = pointer to MemoryMap array in physical memory
;        Exit    returns if MemoryMap is invalid
; -------------------------------------------------------------------------------
        LEAF_ENTRY KernelStart
; add     r0, pc, #g_oalAddressTable - (. + 8)
        mov      r11, r0                         ; (r11) = &MemoryMap (save pointer)

        ; figure out the virtual address of OEMAddressTable
        mov      r1, r11                         ; (r1) = &MemoryMap (2nd argument to VaFromPa)
        bl      VaFromPa
        mov      r6, r0                          ; (r6) = VA of MemoryMap

        ; convert base of PTs to Physical address
        ldr     r4, =PTs                        ; (r4) = virtual address of FirstPT
        mov      r0, r4                          ; (r0) = virtual address of FirstPT
        mov      r1, r11                         ; (r1) = &MemoryMap (2nd argument to PaFromVa)
        bl      PaFromVa

        mov      r10, r0                         ; (r10) = ptr to FirstPT (physical)

;        Zero out page tables & kernel data page

        mov      r0, # 0                           ; (r0-r3) = 0's to store
        mov      r1, # 0
        mov      r2, # 0
        mov      r3, # 0
        mov      r4, r10                         ; (r4) = first address to clear
        add      r5, r10, #KDEnd-PTs             ; (r5) = last address + 1
18       stmia   r4!, {r0-r3}
        stmia   r4!, {r0-r3}
        cmp      r4, r5
        blo     %B18


;        Setup 2nd level page table to map the high memory area which contains the
; first level page table, 2nd level page tables, kernel data page, etc.

        add      r4, r10, #HighPT-PTs            ; (r4) = ptr to high page table
        orr     r0, r10, #0x051                 ; (r0) = PTE for 64K, kr/w kr/w r/o r/o page, uncached unbuffered
        str      r0, [r4, #0xD0* 4 ]               ; store the entry into 8 consecutive slots
        str      r0, [r4, #0xD1* 4 ]
        str      r0, [r4, #0xD2* 4 ]
        str      r0, [r4, #0xD3* 4 ]
        add      r8, r10, #ExceptionVectors-PTs  ; (r8) = ptr to vector page
        bl      OEMARMCacheMode                 ; places C and B bit values in r0 as set by OEM
        mov      r2, r0
        orr     r0, r8, #0x002                  ; construct the PTE
        orr     r0, r0, r2
        str      r0, [r4, #0xF0* 4 ]               ; store entry for exception vectors
        orr     r0, r0, #0x500                  ; (r0) = PTE for 4k r/o r/o kr/w kr/w C+B page
        str      r0, [r4, #0xF4* 4 ]               ; store entry for abort stack
        str      r0, [r4, #0xF6* 4 ]               ; store entry for FIQ stack  (access permissions overlap for abort and FIQ stacks, same 1k)
        orr     r0, r8, #0x042
        orr     r0, r0, r2                      ; (r0)= PTE for 4K r/o kr/w r/o r/o (C+B as set by OEM)
        str      r0, [r4, #0xF2* 4 ]               ; store entry for interrupt stack
        add      r9, r10, #KPage-PTs             ; (r9) = ptr to kdata page
        orr     r0, r9, #0x002
        orr     r0, r0, r2                      ; (r0)=PTE for 4K (C+B as set by OEM)
        orr     r0, r0, #0x250                  ; (r0) = set perms kr/w kr/w kr/w+ur/o r/o
        str      r0, [r4, #0xFC* 4 ]               ; store entry for kernel data page
        orr     r0, r4, #0x001                  ; (r0) = 1st level PTE for high memory section
        add      r1, r10, #0x4000
        str      r0, [r1, #- 4 ]                   ; store PTE in last slot of 1st level table
  IF {FALSE}
        mov      r0, r4
        mov      r1, # 256                         ; dump 256 words
        CALL     WriteHex
  ENDIF

;        Fill in first level page table entries to create "un-mapped" regions
; from the contents of the MemoryMap array.
;
;        (r9) = ptr to KData page
;        (r10) = ptr to 1st level page table
;        (r11) = ptr to MemoryMap array

        add      r10, r10, #0x2000               ; (r10) = ptr to 1st PTE for "unmapped space"
        mov      r7, # 2                           ; (r7) = pass counter

        mov      r0, #0x02
        orr     r0, r0, r2                      ; (r0)=PTE for 0: 1MB (C+B as set by OEM)
        orr     r0, r0, #0x400                  ; set kernel r/w permission
20       mov      r1, r11                         ; (r1) = ptr to MemoryMap array


25       ldr     r2, [r1], # 4                     ; (r2) = virtual address to map Bank at
        ldr     r3, [r1], # 4                     ; (r3) = physical address to map from
        ldr     r4, [r1], # 4                     ; (r4) = num MB to map

        cmp      r4, # 0                           ; End of table?
        beq     %F29

        ldr     r5, =0x1FF00000
        and      r2, r2, r5                      ; VA needs 512MB, 1MB aligned.

        ldr     r5, =0xFFF00000
        and      r3, r3, r5                      ; PA needs 4GB, 1MB aligned.

        add      r2, r10, r2, LSR # 18
        add      r0, r0, r3                      ; (r0) = PTE for next physical page

28       str      r0, [r2], # 4
        add      r0, r0, #0x00100000             ; (r0) = PTE for next physical page

        sub      r4, r4, # 1                       ; Decrement number of MB left
        cmp      r4, # 0
        bne     %B28                            ; Map next MB

        bic     r0, r0, #0xF0000000             ; Clear Section Base Address Field
        bic     r0, r0, #0x0FF00000             ; Clear Section Base Address Field
        b       %B25                            ; Get next element


29
        bic     r0, r0, #0x0C                   ; clear cachable & bufferable bits in PTE
        add      r10, r10, #0x0800               ; (r10) = ptr to 1st PTE for "unmapped uncached space"
        subs    r7, r7, # 1                       ; decrement pass counter
        bne     %B20                            ; go setup PTEs for uncached space if we're not done
        sub      r10, r10, #0x3000               ; (r10) = restore address of 1st level page table
  IF {FALSE}
        mov      r0, r10
        mov      r1, # 4096                        ; dump 4096 words
        CALL     WriteHex
  ENDIF

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上面的代码已经很多注释，已经非常明了了，我就不多废话了。

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MMU，cache，TTB设置

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现在，大体的方法明白了 

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一些重要的汇编宏定义

  
  
  
  

   
   
   
   
 
    
MACRO
 
    
        mtc15   $cpureg, $cp15reg
 
    
        mcr     p15,0,$cpureg,$cp15reg,c0,0
 
    
        MEND
 
    
 
    
        MACRO
 
    
        mfc15   $cpureg, $cp15reg
 
    
        mrc     p15,0,$cpureg,$cp15reg,c0,0
 
    
MEND
 
   
  
  
  
  
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Assembly code

    
    
    
    

     
     
     
     
     ;
     
     
     
      The page tables and exception vectors are setup. Initialize the MMU and turn it on.
     
     
     
      ;
     
     
     
     页表和异常向量表建立之后，初始化MMU并打开
     
     
     
      
     
     
     
      
     
     
     
     mov
     
     
     
      r1, #
     
     
     
     1
     
     
     
      mtc15 r1, c3 
     
     
     
     ;
     
     
     
      Setup access to domain 0 and clear other
     
     
     
      
     
     
     
      
     
     
     
     ;
     
     
     
      domains including 15 for PSL calls (see above)
     
     
     
      
     
     
     
      mtc15 r10, c2 
     
     
     
     ;
     
     
     
     ;mtc15 是宏定义 把TTB（L1转换基地址放到C2）
     
     
     
      
     
     
     
      
     
     
     
     mov
     
     
     
      r0, #
     
     
     
     0
     
     
     
      mcr p15, 
     
     
     
     0
     
     
     
     , r0, c8, c7, 
     
     
     
     0
     
     
     
      
     
     
     
     ;
     
     
     
      Flush the I&D TLBs
     
     
     
      
     
     
     
      mfc15 r1, c1 
     
     
     
     ;
     
     
     
     mfc15 宏定义 读出C1的值到r1
     
     
     
      
     
     
     
      orr r1, r1, #0x007F 
     
     
     
     ;
     
     
     
      changed to read-mod-write for ARM920 Enable: MMU, Align, DCache, WriteBuffer
     
     
     
      
     
     
     
      orr r1, r1, #0x3200 
     
     
     
     ;
     
     
     
      vector adjust, ICache, ROM protection
     
     
     
      
     
     
     
      ldr r0, VirtualStart 
     
     
     
     ;
     
     
     
     这个很关键在代码中有 VirtualStart DCD VStart
     
     
     
      
     
     
     
      
     
     
     
     cmp
     
     
     
      r0, #
     
     
     
     0
     
     
     
      
     
     
     
     ;
     
     
     
      make sure no stall on "mov pc,r0" below
     
     
     
      
     
     
     
      mtc15 r1, c1 
     
     
     
     ;
     
     
     
      enable the MMU & Caches
     
     
     
      
     
     
     
      
     
     
     
     mov
     
     
     
      pc, r0 
     
     
     
     ;
     
     
     
      & jump to new virtual address 跳到VStart运行
     
     
     
      
     
     
     
      
     
     
     
     nop
    
    
    
    

总结：填写好二级页表，把二级页表的首地址存放到一级页表的表项最后最后；根据OEMAddresstable初始化L1页表；把L1的转换表的基地址放到协处理器的c1的寄存器。启动MMU等功能即可。 
——现在基本没有什么疑问了，完成博客，今天晚上回去结贴。——目前对于一些domain、AP的设置等还是不是很明白。不过都是一个样，看看数据手册即可。阿门！大功告成。 

如果还有疑问，请看CSDN论坛帖子： http://topic.csdn.net/u/20081231/10/bbde79c2-2884-48e3-9718-90d7fcc1afa8.html?seed=1947589160

这个讲的较详细。哈哈，最难的都理解了。我对ARM越来越有信心。

http://www.cnblogs.com/we-hjb/archive/2008/10/12/1309596.html 
——这篇博客也讲得比较好，值得参考。

转载请标明:作者wogoyixikexie@gliet.桂林电子科技大学一系科协，原文地址：http://blog.csdn.net/gooogleman——如有错误，希望能够留言指出;如果你有更加好的方法，也请在博客后面留言，我会感激你的批评和分享。