＃定义与枚举解决外设 [英] #define vs. enums for addressing peripherals

问题描述

我要在基于ARM9微控制器外设寄存器进行编程。

I have to program peripheral registers in an ARM9-based microcontroller.

例如，对于USART，我相关的存储器地址存储在一个枚举：

For instance, for the USART, I store the relevant memory addresses in an enum:

enum USART
{
    US_BASE = (int) 0xFFFC4000,
    US_BRGR = US_BASE + 0x16,
    //...
};

然后，我用指针的函数来初始化寄存器：

Then, I use pointers in a function to initialize the registers:

void init_usart (void)
{
    vuint* pBRGR = (vuint*) US_BRGR;
    *pBRGR = 0x030C;
    //...
}

但我的老师说我最好使用的#define S，如：

#define US_BASE (0xFFFC4000)
#define US_BRGR (US_BASE + 0x16)
#define pBRGR   ((vuint*) US_BRGR)

void init_usart (void)
{
    *pBRGR = 0x030C;
}

就像这样，他说，你没有在堆栈中分配指针的开销。

Like so, he says, you don't have the overhead of allocating pointers in the stack.

就个人而言，我不喜欢的#define 取值多少，也没有其他的preprocessor指令。
所以，问题是，在这种特殊情况下，为的#define 真是值得使用的，而不是枚举和stack-分配的指针？

Personally, I don't like #defines much, nor other preprocessor directives. So the question is, in this particular case, are #defines really worth using instead of enums and stack-allocated pointers?

相关问题：要配置的ARM9特定的外设寄存器基于芯片的

推荐答案

我有这种方法总是preferred是先定义一个结构反映了外设寄存器布局

The approach I've always preferred is to first define a struct reflecting the peripherals register layout

typedef volatile unsigned int reg32; // or other appropriate 32-bit integer type
typedef struct USART
{
    reg32 pad1;
    reg32 pad2;
    reg32 pad3;
    reg32 pad4;
    reg32 brgr;
    // any other registers
} USART;

USART *p_usart0 = (USART * const) 0xFFFC4000;

然后在code，我可以只使用

Then in code I can just use

p_usart0->brgr = 0x030C;

这方法是干净多了，当你有相同的排序周边的多个实例：

This approach is much cleaner when you have multiple instances of the same sort of peripheral:

USART *p_usart1 = (USART * const) 0xFFFC5000;
USART *p_usart2 = (USART * const) 0xFFFC6000;

用户sbass提供的链接<一个href=\"http://www.embedded.com/design/programming-languages-and-tools/4027659/Alternative-Models-for-Memory-Mapped-Devices\"相对=nofollow>由Dan Saks的一个很好的列，让这种技术更多的细节，并在其他方法指出了它的优势。

User sbass provided a link to an excellent column by Dan Saks that gives much more detail on this technique, and points out its advantages over other approaches.

如果你有幸使用C ++，那么你可以添加方法对周围所有的常用操作，并很好地封装设备的特殊性。为

If you're lucky enough to be using C++, then you can add methods for all the common operations on the peripheral and nicely encapsulate the devices peculiarities.

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