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# MMU
## 1. 概述
- 虚拟内存系统（VMSA）提供了一套内存管理单元（MMU）， 它控制着地址转换、访问权限和内存属性的确定和检查。
- 地址转换过程将CPU使用的虚拟地址(VAs)映射到物理内存系统的物理地址(PAs)上。
- 在本SDK中 aarch32 state 采用 section 格式的转换表
- 在本SDK中 aarch64 state 采用 4KB 粒度 格式的转换表
## 2. 功能
- MMU功能支持用户根据需要修改MMU表的默认内存属性。
## 3. 配置方法
## 4. 应用示例
"baremetal/example/system/amp/libmetal_test"
"baremetal/example/system/amp/openamp"
## 5. API参考
### 5.1 用户定义
/* 访问权限 */
```
#define MT_P_NA_U_NA /* higher Exception level access=NA, user=NA */
#define MT_P_RW_U_NA /* higher Exception level access=RW, user=NA */
#define MT_P_RW_U_RO /* higher Exception level access=RW, user=RO */
#define MT_P_RW_U_RW /* higher Exception level access=RW, user=RW */
#define MT_P_RO_U_NA /* higher Exception level access=RO, user=NA */
#define MT_P_RO_U_RO /* higher Exception level access=RO, user=RO */
```
/* 内存属性参数 */
```
#define MT_DEVICE_NGNRNE /* Device-nGnRnE , Outer Shareable */
#define MT_DEVICE_NGNRE /* Device-nGnRE , Outer Shareable */
#define MT_NORMAL_WT /* Outer and Inner Write-Through, Read-Allocate No Write-Allocate , Outer Shareable */
#define MT_NORMAL_WB_WCN /* Outer and Inner Write-Back, Read-Allocate No Write-Allocate , Outer Shareable */
#define MT_NORMAL_NC /* Outer and Inner Non-cacheable , Outer Shareable , Outer Shareable */
#define MT_NORMAL /* Outer and Inner Write-Back, Read-Allocate Write-Allocate , Outer Shareable , Outer Shareable */
```
### 5.2 用户API接口
- 此函数用于配置转换表中地址对应条目的内存属性与访问权限
```c
void FSetTlbAttributes(uintptr addr, fsize_t size, u32 attrib);
```
Note:
aarch32 state 采用 section 页表，由此addr 建议采用1MB 地址对齐，size 建议为MB的整数倍。
aarch64 state 采用 4KB 粒度 页表，由此addr 建议采用4KB 地址对齐，size 建议为4KB的整数倍。
Input:
- addr ， 需要为内存区域设置属性与权限的起始地址
- size ， 内存区域的范围
- attrib，指定内存区域的属性 ,内存属性的取值由 访问权限 与 内存属性参数 组成，具体类型参考 ### 5.1 用户定义
Return:
- void
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