關(guān)于ARM9協(xié)處理器CP15及MCR和MRC指令
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寄存器1：Control register
對該寄存器讀寫指令如下：
MRC
MCR
該寄存器功能如下表
Registe bits | Name | Function | Value |
31 | iA bit | Asynchronous clock select | |
30 | nF bit | notFastBus select | |
29:15 | Read = Unpredictable Write = should be zero | ||
14 | RR bit | Round robin replacement | 0 = Random replacement 1 = Round robin replacement |
13 | V bit | Base location of exception register(異常寄存器基地址) | 0 = Low address = 0x0000 0000 1 = High address = 0xFFFF 0000 |
12 | I bit | Instruction cache enable | 0 = Instruction cache disable 1 = Instruction cache enable |
11:10 | Reserved | Read = 00 Write = 00 | |
9 | R | ROM protection | |
8 | S | System protection | |
7 | B | Big-endian/little-endian | 0 = Little-endian operation 1 = Big-endian operation |
6:3 | Read = 1111 Write = 1111 | ||
2 | C bit | Data cache enable | 0 = data cache disable 1 = data cache enable |
1 | A bit | Alignment fault enable | Data address alignment fault checking (地址對齊檢查) 0 = 1 = |
0 | M bit | MMU enable | 0 = MMU disable 1 = MMU enable |
Clocking mode(時鐘模式) | iA | |
Fastbus mode (快速總線模式) | ||
Reserved | ||
Synchronous (同步模式) | ||
Asynchronous (異步模式) |
寄存器2：Translation Table Base(TTB) Register
Register bits | Function |
31:14 | Pointer to first level translation table base . |
13:0 | Reserved Read = Unpredictable Write = Should be zero |
訪問C2寄存器指令如下：
MRC
MCR
該寄存器存放第一級轉(zhuǎn)換表基地址。寫入時，位[13：0]必須為0，讀出時，位[13：0]的值不可預(yù)知。
寄存器3：Domain Access Control Register
寄存器3是可讀寫的域訪問控制寄存器，分為16組，每組占用2個位
訪問該寄存器的指令如下：
MRC
MCR
Interpreting Access Control Bits in Domain Access Control Register
寄存器4：保留
對該寄存器的讀寫會產(chǎn)生不可預(yù)料的結(jié)果。
寄存器5：Fault Status Register
寄存器6：Fault Address Register
寄存器7：Cache Operations
該寄存器是只寫寄存器，用于管理指令緩存和數(shù)據(jù)緩存。
對該寄存器的寫操作所實現(xiàn)的功能，是通過MCR指令中的opcode_2和CRm兩者的組合來選擇的，具體組合如下。
寄存器8：TLB Operations
Register 8 is a write-only register used to manage the translation lookaside buffer(TLBs),the instruction TLB and the data TLB.
Five TLB operations are defined and the function to be performed is selected by the opcode_2 and CRm fields in the MCR instruction used to write CP15 register 8.Writing other opcode_2 or CRm values id unpredictable. Reading from CP15 register 8 is unpredictable.
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