@符号在C变量声明 [英] @ sign in C variable declaration
问题描述
我发现通过pic1250.h的名称PIC单片机这个头文件，我无法得到它使用的一些语法的窍门。
I found this header file for PIC microcontrollers by the name of pic1250.h and I'm unable to get the hang of some syntax used in it.
该文件的来源是：
/*
* Header file for the Microchip
* PIC 12c508 chip
* PIC 12c509 chip
* Baseline Microcontrollers
*/
static volatile unsigned char RTCC @ 0x01;
static volatile unsigned char TMR0 @ 0x01;
static volatile unsigned char PCL @ 0x02;
static volatile unsigned char STATUS @ 0x03;
static unsigned char FSR @ 0x04;
static volatile unsigned char OSCCAL @ 0x05;
static volatile unsigned char GPIO @ 0x06;
static unsigned char control OPTION @ 0x00;
static volatile unsigned char control TRIS @ 0x06;
/* STATUS bits */
static bit GPWUF @ (unsigned)&STATUS*8+7;
static bit PA0 @ (unsigned)&STATUS*8+5;
static bit TO @ (unsigned)&STATUS*8+4;
static bit PD @ (unsigned)&STATUS*8+3;
static bit ZERO @ (unsigned)&STATUS*8+2;
static bit DC @ (unsigned)&STATUS*8+1;
static bit CARRY @ (unsigned)&STATUS*8+0;
/* OPTION bits */
#define GPWU (1<<7)
#define GPPU (1<<6)
#define T0CS (1<<5)
#define T0SE (1<<4)
#define PSA (1<<3)
#define PS2 (1<<2)
#define PS1 (1<<1)
#define PS0 (1<<0)
/* OSCCAL bits */
static bit CAL7 @ (unsigned)&OSCCAL*8+7;
static bit CAL6 @ (unsigned)&OSCCAL*8+6;
static bit CAL5 @ (unsigned)&OSCCAL*8+5;
static bit CAL4 @ (unsigned)&OSCCAL*8+4;
/* GPIO bits */
static bit GP5 @ (unsigned)&GPIO*8+5;
static bit GP4 @ (unsigned)&GPIO*8+4;
static bit GP3 @ (unsigned)&GPIO*8+3;
static bit GP2 @ (unsigned)&GPIO*8+2;
static bit GP1 @ (unsigned)&GPIO*8+1;
static bit GP0 @ (unsigned)&GPIO*8+0;
#define CONFIG_ADDR 0xFFF
#define FOSC0 0x01
#define FOSC1 0x02
#define WDTE 0x04
#define CP 0x08
#define MCLRE 0x0F
我无法了解整个修改器，数据类型@声明出头。是否有人可以帮助我吗？我在此只是个新手。
I'm unable to understand the whole modifer-datatype @ declaration-something. Can someone please help me out? I'm just a newbie at this.
推荐答案
这是一个编译器扩展。
从PIC MPLAB XC8 编译器文档（重点煤矿）：
From PIC MPLAB XC8 compiler documentation (emphasis mine):
5.5.4绝对变量
大多数变量可以在一个绝对地址与下面的声明位于
构建@地址，其中地址是在内存中的位置在哪里
变量是被定位。这样的变量被称为绝对变量
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.
5.5.4.1绝对变量数据存储器
5.5.4.1 ABSOLUTE VARIABLES IN DATA MEMORY
绝对变量主要用于与等同一个C标识符的地址
特殊功能寄存器，但可以用来放置普通变量在绝对
解决数据存储。
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.
例如：
挥发性unsigned char型Portvar @ 0×06;
将声明一个称为Portvar变量位于在数据存储器06h中。编译器
会预留存储该对象（如果地址落入通用RAM）和
将等同变量的标识符到该地址。
will declare a variable called Portvar located at 06h in the data memory. The compiler will reserve storage for this object (if the address falls into general-purpose RAM) and will equate the variable’s identifier to that address.
注意，MPLAB XC8是不是有同样的 @ 结构将对象放置在特定的存储位置仅有的编译器。
Note that MPLAB XC8 is not the only compiler to have the same @ construct to place an object in the specific memory location.
另一个公知的编译器是Freescale codeWarrior（至少HCS08）
Another well known compiler is Freescale CodeWarrior (at least for HCS08).
另外一个是IAR C编译器（至少MSP430和AVR）。
Another one is IAR C Compiler (at least for MSP430 and AVR).
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