初次接触嵌入式开发，请教一个问题，希望大侠们指教

[wwangxt]

问一个问题，在开发基于at91rm9200的驱动时在访问I/O端口时，在linux系统下我如何来访问这个I/O端口，可以直接通过物理地址 就行访问么？我如果这样写#define PIOA_PER (*(volatile unsigned *)0xfffff400)定义了该端口，然后通过这样PIOA_PER ｜＝0x00000001对其进行赋值是否可行，还是通过ioremap函数将其定位到内核的虚拟地址然后进行访问？希望大侠们帮我指点一下，不胜感激！

[bienilz]

在 LDD 中的 Communication with Hardware 中的 Platform Dependencies 中是这样描述的：

• ARM
  
  Ports are memory-mapped, and all functions are supported; string functions are
  implemented in C. Ports are of type unsigned int.

Accessing I/O Memory 中又讲到：

• To read from I/O memory, use one of the following:
  unsigned int ioread8(void *addr);
  unsigned int ioread16(void *addr);
  unsigned int ioread32(void *addr);
  Here, addr should be an address obtained from ioremap (perhaps with an integer offset);
  the return value is what was read from the given I/O memory.
  There is a similar set of functions for writing to I/O memory:
  void iowrite8(u8 value, void *addr);
  void iowrite16(u16 value, void *addr);
  void iowrite32(u32 value, void *addr);

所以按我的理解，应该要用 ioremap 函数。