1.MMU功能

将虚拟地址转化为物理地址；
访问权限管理。

2.地址转化

2.1 总体分析

MMU

2.2 一级转换格式

MMU

位解释：（段设置）

B：表示是否使能write buffer；

C: 表示是否开启cache；

XN（The Execute-Never ）：determines if the region is Executable (0) or Not-executable(1)。

Domain：the ARM1176JZF-S supports 16 Domains in the Secure world and 16 Domains in the Non-secure world. Domains provide support for multi-user operating systems.
P：If the P bit is supported and set for the memory region, it indicates to the system memory controller that this memory region has ECC enabled. ARM1176JZF-S processors do not support the P bit. （设为0）
AP：访问权限

APX：provides an extra access permission bit.
TEX：remap bit

S:determines if the translation is for Non-Shared (0), or Shared (1)memory.

nG：determines if the translation is marked as global (0), or process-specific (1) in the TLB.
NS:The Non-secure (NS) bit determines if the program execution is in the Secure or Non-secure world.

3.MMU配置与使用

3.1 建立一级页表

 void create_page_table(void)

 {

     unsigned long *ttb = (unsigned long *)0x50000000;

     unsigned long vaddr, paddr;

     vaddr = 0xA0000000;

     paddr = 0x7f000000;

     *(ttb + (vaddr >> )) = (paddr & 0xFFF00000) | MMU_SECDESC;

     vaddr = 0x50000000;

     paddr = 0x50000000;

     while (vaddr < 0x54000000)

     {

         *(ttb + (vaddr >> )) = (paddr & 0xFFF00000) | MMU_SECDESC_WB;

         vaddr += 0x100000;

         paddr += 0x100000;

     }

 }

create_page_table

3.2 初始化MMU

 void mmu_init()

 {

    __asm__(

     /*设置TTB*/

     "ldr    r0, =0x50000000\n"

     "mcr    p15, 0, r0, c2, c0, 0\n"    

     /*不进行权限检查*/

     "mvn    r0, #0\n"

     "mcr    p15, 0, r0, c3, c0, 0\n"    

    /*使能MMU*/

     "mrc    p15, 0, r0, c1, c0, 0\n"

     "orr    r0, r0, #0x0001\n"

     "mcr    p15, 0, r0, c1, c0, 0\n"

     :

     :

   );

 }

void mmu_init

3.3 主函数

#define GPKCON (volatile unsigned long*)0xA0008800

#define GPKDAT (volatile unsigned long*)0xA0008808

/*

 * 用于段描述符的一些宏定义

 */

#define MMU_FULL_ACCESS     (3 << 10)   /* 访问权限 */

#define MMU_DOMAIN          (0 << 5)    /* 属于哪个域 */

#define MMU_SPECIAL         (1 << 4)    /* 必须是1 */

#define MMU_CACHEABLE       (1 << 3)    /* cacheable */

#define MMU_BUFFERABLE      (1 << 2)    /* bufferable */

#define MMU_SECTION         (2)         /* 表示这是段描述符 */

#define MMU_SECDESC         (MMU_FULL_ACCESS | MMU_DOMAIN | MMU_SPECIAL | MMU_SECTION)

#define MMU_SECDESC_WB      (MMU_FULL_ACCESS | MMU_DOMAIN | MMU_SPECIAL | MMU_CACHEABLE | MMU_BUFFERABLE | MMU_SECTION)

int main()

{

    create_page_table();

    mmu_init();

    *(GPKCON) = 0x11110000;

    *(GPKDAT) = 0xa0;

    return ;

}

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MMU