c - 我们在嵌入式 c 或嵌入式 c++ 中有 '@' 运算符吗？如果是，请向我解释以下代码？

Question

代码:

static volatile unsigned char   TMR0    @ 0x01;

static volatile unsigned char   PORTA   @ 0x05;

static volatile unsigned char   PORTB   @ 0x06;

static volatile unsigned char   PORTC   @ 0x07;

此代码来自PIC16F877A的HT-PICC编译器pic.h库文件

我理解 static volatile 和其他关键字的含义。 这里 Timer0 寄存器地址是 0x01 但为什么他们在它前面使用 @？跟指针有关系吗？

Answer 1

它是许多嵌入式编译器中常见的编译器扩展，允许您将变量放置在绝对内存地址中。

来自 HI-TECH C 编译器手册:

3.5.4 Absolute Variables

Most variables can be located at an absolute address by following its declaration with the construct @ address, where address is the location in memory where the variable is to be positioned. Such a variables is known as an absolute variables.

3.5.4.1 ABSOLUTE VARIABLES IN DATA MEMORY

Absolute variables are primarily intended for equating the address of a C identifier with a special function register, but can be used to place ordinary variables at an absolute address in data memory.

在你的例子中:

static volatile unsigned char   TMR0    @ 0x01;

TMR0 大概是 8 位无符号硬件寄存器，位于地址 0x01。