How to define global absolute constants

Miguel S

Intellectual 830 points

Hi,

I need to define global constants that are visible for both .asm and .c files.

I have resolved this using the .set + .global directives:

__NO .set 0

__YES .set 1

.global __NO, __YES

Then, I reference these constants in C:

extern unsigned int _NO;

extern unsigned int _YES;

#define NO ((UINT)(&_NO))

#define YES ((UINT)(&_YES))

This way, I use the constants as if they were defined in C. I have checed the assembly code generated from the C code, and everything is correct.

The only problem is that the compiler shows the following warning each time I assign one of these constants to a 16-bit variable:

warning: integer conversion resulted in truncation

I guess this is because the constant is considered to have more than 16 bits. So, Is there a way to define a constant globally (visible for .asm and .C files) and avoid this warning?

Thanks in advance,

Miguel

over 13 years ago

0 Archaeologist over 13 years ago

TI__Guru* 84285 points

You are defining these constants as linker constants, which will cripple potential optimizations of the constants. Try:

x.h

#define NO 0
#define YES 1

x.asm

        .cdecls LIST, "x.h"
        .word YES
        .word NO

0 Miguel S over 13 years ago in reply to Archaeologist

Intellectual 830 points

I have tried that, but it didn't work

I get the following messages from the compiler:

[E9999] Syntax Error

[E9999] Invalid mnemonic specified

Should my compiler v3.2.2 recognize the .cdecls directive?

Regards,

Miguel

0 Archaeologist over 13 years ago in reply to Miguel S

TI__Guru* 84285 points

0640.example.zip

I assume from the compiler version that you are using MSP430 compiler version 3.2.2. Yes, that version of the MSP430 compiler supports .cdecls. Please try the files I have attached.

0 Miguel S over 13 years ago in reply to Archaeologist

Intellectual 830 points

I have tried the files attached and I am getting the same error messages:

[E9999] Syntax Error

[E9999] Invalid mnemonic specified

Regarding my compiler version, it is: cl55 compiler revision 3.2.2

Should the example files work with that compiler revision?

Regards,

Miguel

0 Archaeologist over 13 years ago in reply to Miguel S

TI__Guru* 84285 points

That version of the C5500 compiler (and assembler) does support .cdecls. However, the C5500 assembly only supports .cdecls in algebraic mode. You would have to write the assembly file in algebraic notation and use the '-mg' compiler option.

Your best bet may be to maintain two header files defining these constants, one in C syntax, and one in assembly syntax.

0 Miguel S over 13 years ago in reply to Archaeologist

Intellectual 830 points

OK.

That's not good news for me. I will finally have to maintain two header files. That's what I was tryint not to do.

Thanks for your answers.

Miguel

Processors

Processors forum

How to define global absolute constants