How to use global variable in assembly function.

Silpa M

Hello,

1.How to use global variable in "asm" function which is declared in "c" file

2.How to copy the registers(ex R14,R15) to a global variable and how to store them back to the registers from Global variables.

Please share if there is any examples for the above queries.

Thanks in Advance.

Regards,

Shilpa

over 13 years ago

0 Zhaohong Zhang over 13 years ago

TI__Mastermind 22715 points

Shilpa,

You can try the following example. I assume that you use "eabi" library.

.global Test

.global R14_SAVE

Test:
    ldr R0, R14_SAVE_ ADD   ; Load address for the global variable
    str R14, [R0] ; save R14 to global variable

bx lr

R14_SAVE_ADD .word R14_SAVE

In your C code, you need to define the following.

extern void Test();

extern unsigned int R14_SAVE;

Thanks and regards,

Zhaohong

0 Silpa M over 13 years ago in reply to Zhaohong Zhang

Prodigy 250 points

Thank you Zhang.

Can you tell me how to use #pragma INTERRUPT & #pragma DATA_SECTION in assembly language.

Regards,

Silpa Muppalla

0 Zhaohong Zhang over 13 years ago in reply to Silpa M

TI__Mastermind 22715 points

Silpa,

The pragmas are not applicable for assembly code. If you want to create an assembly ISR, you have to follow alll the requirement from ARM R4 TRM.

Thanks and regards,

Zhaohong

0 Silpa M over 13 years ago in reply to Zhaohong Zhang

Prodigy 250 points

Thank you Zhang..

Can you please tell me how to reserve a register (expression regisrer) for the user means compiler should not use that register as temporary register.

Regards,

Shilpa

0 Zhaohong Zhang over 13 years ago in reply to Silpa M

TI__Mastermind 22715 points

Silpa,

I assume that you are using TI Code Composer. In Code Composer, open the build option for the project. There is a compiling option which allows to reserve registers.

Thanks and regards,

Zhaohong

0 Chuck Davenport over 13 years ago in reply to Zhaohong Zhang

TI__Guru 59540 points

Hello Silpa:

Did the information that Zhaohoang provided help answer your questions? If so, please verify his answer so that we can close the thread. Once the thread is closed, you can open a new thread to get any additional questions answered.

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How to use global variable in assembly function.