请教关于MSP430 inline ASM 的问题

MPY32CTL0在C的头文件中定义了，但是在汇编中没有不认识。有以下两种处理办法：

1、可以将这部分汇编代码放到一个asm文件中，调用汇编函数。

2、从User's Guide中查MPY32CTL0的地址，直接对地址操作。

以下是我从TI的e2e中查找的类似的问题，他提供了一种方式，但是我做实验还是报错，供参考：

P1DIR is actually a C variable that happens to reside right on top of the P1DIR register.

On assembly level, P1DIR is unknown.

Usually, since the position of P1DIR is known at compile time, the compiler will not forward a variable of this name to the linker for later linking. It will use the direct location instead when generating the assembly level code.

In an assembly file, you'd include a different header, where P1DIR would be just a number. But both ways won't help you on inline assembly.

The mspgcc compiler uses an extended syntax for inline assembly. You code would look like that:

asm(" bis.b #0x01, %0":"=m"(P1DIR):);

This tells the compiler that the placeholder %0 is a destination memory location that is associated with the content of the variable P1DIR. Since P1DIR has a fixed memory location, it will generate an instruction like "bis.b #0x01, &0x200".. However, if P1DIR is a local variable on stack something like "bis.b #0x01, 0x02(SP)" will be generated. And if it is a register variable, it will be put on stack first.

If your code requires a register rather than memory, a "=r" will tell the compiler that your ASM instruction is returning something in a register, and will take it and put it into P1DIR. The compiler will choose the register 8one it doesn't need) and insert it into the instruction.

A really smart way to do things - just not easy to understand by the existing documentation.

Whether the comiler you use has something similar, or maybe other means to provide a C variable's location to assembly code, should be written in the compiler documentation.

E.g. you might add the symbol value for P1DIR to the linker script file, so the liker will find it and put it into the assembly instruction at link stage.

Or it may be that the compiler provides assembly-level symbols like _P1DIR for the C variables. It depends on the compiler.