【译】x86程序员手册29-第8章 输入输出

Chapter 8 Input/Output 输入/输出

This chapter presents the I/O features of the 80386 from the following perspectives:

本章从以下方面来介绍80386的I/O特性:

• Methods of addressing I/O ports

I/O端口的寻址方式

• Instructions that cause I/O operations

引起IO操作的指令

• Protection as it applies to the use of I/O instructions and I/O port addresses.

应用在IO指令和IO端口地址的保护措施。

8.1 I/O Addressing IO地址

The 80386 allows input/output to be performed in either of two ways:

80386允许输入/输出用以下两种方式运行：

• By means of a separate I/O address space (using specific I/O instructions)

通过独立的IO地址空间（使用特殊的IO指令）

• By means of memory-mapped I/O (using general-purpose operand manipulation instructions).

通过内存映射（使用通用目的操作数的操作指令）。

8.1.1 I/O Address Space IO地址空间

The 80386 provides a separate I/O address space, distinct from physical memory, that can be used to address the input/output ports that are used for external 16 devices. The I/O address space consists of 2^(16) (64K) individually addressable 8-bit ports; any two consecutive 8-bit ports can be treated as a 16-bit port; and four consecutive 8-bit ports can be treated as a 32-bit port. Thus, the I/O address space can accommodate up to 64K 8-bit ports, up to 32K 16-bit ports, or up to 16K 32-bit ports.

80386从物理内存上明确的提供一个独立的IO地址空间，它们可以用来对外部16位设备的输入输出端口进行寻址。IO地址空间由2^16（64K）大小的独立的可寻址的8位端口组成；任何两个连续的8位端口可以被视做16位端口；四个连接的8位商品可以被视做32位端口。这样，IO地址空间可以容纳最多64K个8位端口，或32K个16位商品，或16K个32位端口。

The program can specify the address of the port in two ways.程序可以使用两种方式指定端口的地址。

Using an immediate byte constant, the program can specify:

使用立即数据字节常量，程序可以指定：

• 256 8-bit ports numbered 0 through 255.

共256个，8位端口号0到255

• 128 16-bit ports numbered 0, 2, 4, . . . , 252, 254.

128个16位端口号，从0，2，4，直到252，254。

• 64 32-bit ports numbered 0, 4, 8, . . . , 248, 252.

64个32位端口号0，4，8，...，248，252。

Using a value in DX, the program can specify:

使用DX寄存器中的值，程序可以指定上：

• 8-bit ports numbered 0 through 65535

8位端口号，从0到65535

• 16-bit ports numbered 0, 2, 4, . . . , 65532, 65534

16位端口号，从0，2，4...，65532，65534

• 32-bit ports numbered 0, 4, 8, . . . , 65528, 65532

32位端口号，从0，4，8，...，65528，65532

The 80386 can transfer 32, 16, or 8 bits at a time to a device located in the I/O space. Like doublewords in memory, 32-bit ports should be aligned at addresses evenly divisible by four so that the 32 bits can be transferred in a single bus access. Like words in memory, 16-bit ports should be aligned at even-numbered addresses so that the 16 bits can be transferred in a single bus access. An 8-bit port may be located at either an even or odd address.

80386可以一次向位于IO空间的设备传送32、16或8位。就象内存中的双字一样，32位端口应当在能被4整除的地址上对齐，这样32位就能在一个单独的总线访问中被传送。就象内存中的字一样，16位端口应当在偶数对齐的地址上，这样16位就能在一个单独的总线访问中被传送。8位端口可以定位在奇数或偶数地址上。

The instructions IN and OUT move data between a register and a port in the I/O address space. The instructions INS and OUTS move strings of data between the memory address space and ports in the I/O address space.

指令IN和OUT通过IO地址空间，在寄存器和端口之间传输数据。指令INS和OUTS在内存地址与IO地址空间中的端口之间传送字符串数据。

8.1.2 Memory-Mapped I/O IO的内存映射

I/O devices also may be placed in the 80386 memory address space. As long as the devices respond like memory components, they are indistinguishable to the processor.

IO设备也可以被放在80386的内存地址空间。由于设备响应就象内存组件一样，对于处理器平说，几乎没有什么区别。

Memory-mapped I/O provides additional programming flexibility. Any instruction that references memory may be used to access an I/O port located in the memory space. For example, the MOV instruction can transfer data between any register and a port; and the AND, OR, and TEST instructions may be used to manipulate bits in the internal registers of a device (see Figure 8-1 ). Memory-mapped I/O performed via the full instruction set maintains the full complement of addressing modes for selecting the desired I/O device (e.g., direct address, indirect address, base register, index register, scaling).

IO内存映射提供额外的程序的便利性。任何内存引用指令都可以被用来访问一个被映射到内存空间的IO端口。例如，MOV指令可以在任何寄存器与端口之间传送数据；AND、OR和TEST指令也可被用来操作设备内部寄存器上的位（见图8-1）。IO内存映射通过全部指令集，对选定的需求IO设备允许使用全部可用的寻址模式（如：直接寻址，间接寻址，基址寄存器寻址，索引寄存器寻址，以比例因子寻址）。

Memory-mapped I/O, like any other memory reference, is subject to access protection and control when executing in protected mode. Refer to Chapter 6 for a discussion of memory protection.

IO内存映射，就象其他的内存引用一样，在保护模式下，也是访问控制和保护的主题。参见第6章关于内存保护的讨论。