问题描述
我必须在基于ARM9的微控制器中编程外设寄存器。
I have to program peripheral registers in an ARM9-based microcontroller.
例如，对于USART，我将相关内存地址存储在枚举：
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，我使用函数中的指针来初始化寄存器：
Then, I use pointers in a function to initialize the registers:
void init_usart (void)
{
vuint* pBRGR = (vuint*) US_BRGR;
*pBRGR = 0x030C;
//...
}
但是我的老师说我会更好地使用 #define s，例如：
But my teacher says I'd better use #defines, such as:
#define US_BASE (0xFFFC4000)
#define US_BRGR (US_BASE + 0x16)
#define pBRGR ((vuint*) US_BRGR)
void init_usart (void)
{
*pBRGR = 0x030C;
}
像这样，他说，你没有分配指针的开销在堆栈中。
Like so, he says, you don't have the overhead of allocating pointers in the stack.
个人而言，我不喜欢 #define ，也不是其他预处理指令。
所以问题是，在这种特殊情况下， #define 真的值得使用，而不是枚举 s和堆栈分配的指针？
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?
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推荐答案
我一直喜欢的方法是首先定义反映外设寄存器布局的结构
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;
然后在代码中我可以使用
Then in code I can just use
p_usart0->brgr = 0x030C;
当您有多个外设相同类型的实例时，这种方法会更加清晰：
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提供了一个链接到，以及指出其优于其他方法的优势。
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.
如果你很幸运地使用C ++，那么你可以添加外设上所有常见操作的方法，并且很好地封装设备特性。
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.
这篇关于#define与枚举寻址外设的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！