`

关于IO ports和IO memory

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在IA32 Manuals-Basic Architecture中， 对于IO有二种寻址方式：1, IO Port(IO Address Space); 2,
Memory-Mapped IO.

        1) IO Port方式.
        使用体系结构相关的in/out指令来访问IO端口，并且能够保证每一条指令都在下一条之前完成，也就是in/out
指令是自然有序的。 一共有2^16(64K)个单独的8-bit端口，编号从0到FFFFH(其中从0F8H到0FFH被保留),任意两个连续
的8bit端口可以被看做是一个16bit端口，同样，任意4个连续的8bit端口可以被看做是一个32bit端口。

        2) IO Address Space方式.
        可以使用任意的mov、and、or等指令来访问，就象访问主存一样。

        对于Linux内核来说，若想访问io ports，需要request_region来分配io ports， 返回之后的struct resource
就包含了start和end，在此之间的区域可以用in/out指令来访问。 /proc/ioports记录了目前已分配的所有IO端口。
        对memory-mapped io来说，需要request_mem_region来分配IO内存（也就是外设的寄存器或者存储体），它也是
返回一个struct resource结构，其中有start和end字段，可以用来作为ioremap函数的参数。 对request_mem_region分配
的IO内存进行了ioremap之后，就可以在程序中象访问普通内存区那样来访问它们了。
        IO Ports和IO Momory之间的转换，可以用ioport_map/ioport_unmap来实现。

 

Quote : http://linux.chinaunix.net/bbs/viewthread.php?tid=890288&page=1#pid6311319

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