why C callable assembly function?

Naveen Rangu

Intellectual 600 points

Hi,

could anyone tell me about C Callable assembly functions? why it will be useful ?

I am not understanding why these files are written in ASM language instead of C languge

is it okay to write this asm files in c language

please help me

Thanks & regards,

Naveen Rangu

over 16 years ago

0 BrandonAzbell over 16 years ago

TI__Guru 64820 points

Naveen Rangu said:

could anyone tell me about C Callable assembly functions? why it will be useful ?

Generally this is done to optimize a particular function for the purpose of speed of execution. While a C compiler may be good at producing efficient code from a space and speed standpoint, hand optimized assembly designed code can offer even more performance.

This comes at a cost of development, portability and maintenance.

Naveen Rangu said:

is it okay to write this asm files in c language

Certainly.

0 Lori Heustess over 16 years ago in reply to BrandonAzbell

TI__Guru* 93800 points

Adding to Brandon's reasons

- You may require precise timing in the routine and don't want it tied to the compiler version or optimization level. For example a delay() function (wait so many uS).

- You may want to access CPU resources that are not accessible in C directly. This is a very rare case - but for 28x CPU the DBGIER register is one I can think of.

Cheers

Lori

0 Naveen Rangu over 16 years ago in reply to Lori Heustess

Intellectual 600 points

Thank you Lori

0 Naveen Rangu over 16 years ago in reply to BrandonAzbell

Intellectual 600 points

Thank You Brandon

0 MikeH over 15 years ago in reply to BrandonAzbell

Guru 15580 points

Brandon, Lori,

Can either of you point me the documentation for writing c-callable asm functions? I have looked thru both the SPRU281F Compiler User Guide and the SPRU280H Assy User Guide and do not see any reference to c-callable functions.....unless I missed something.

thx

MikeH

0 Lori Heustess over 15 years ago in reply to MikeH

TI__Guru* 93800 points

MikeH said:
Can either of you point me the documentation for writing c-callable asm functions? I have looked thru both the SPRU281F Compiler User Guide and the SPRU280H Assy User Guide and do not see any reference to c-callable functions.....unless I missed something.

Mike

The key is to follow the calling conventions for the compiler. These are described in the compiler ref guide http://www.ti.com/lit/spru514.

Also see this wiki article:

http://processors.wiki.ti.com/index.php/C28x_Code_Generation_Tips_and_Tricks#Q:_I_have_a_function_in_assembly_and_I_want_to_call_it_from_C_-_How_can_I_access_the_arguments_inside_the_function.3F

Regards,

-Lori

0 MikeH over 15 years ago in reply to Lori Heustess

Guru 15580 points

Thanks Lori.

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why C callable assembly function?