Question about register usage in C called assembly code for C6000

Rather than write hand-coded assembly, you should consider implementing this function in linear assembly.  This is a level of programming abstraction that is between C and assembly.  Please see the chapter titled Using the Assembly Optimizer in the C6000 C manual.  Among other benefits, you can use the directives .cproc and .endproc around your assembly function, and that will take care of all these register convention details for you.  

For now, I presume you still want to implement in hand coded assembly.

Robert W said:

What registers should I save in assembly code?

Please show me the C prototype for this assembly function.  Then I can show you which registers will have the input parameters and which register to use to return the result.

Robert W said:

I notice that A0 to A9 are reserved by parent function while others reserved for child.

Any register noted as preserved by parent can be modified in your assembly function without having to worry that you are messing up something in the calling function.  Try to avoid using any register noted as preserved by child.  If you do change one of those registers, you need to add code at the beginning and end of the function to save and restore it.

Thanks and regards,

-George

Thank you George!

The main C code is like this:

int main()
{
short ii=256;
int dec_out[256/32];
int trace_bk[256*2];
int i;

// initialize decoded data array
for (i=0; i<256/32; i++)
{
dec_out[i]=0;
}

// call assembly decode algorithm
vtbasmfunc(data_in, dec_out, trace_bk, ii, metrics);
// print out decode data in hex, reversed bit format,
for (i=0; i<256/32; i++)
{
printf("data_out[%d]=%X\n", i, dec_out[i]);
}

return 1;

}

In asm code, almost all registers are used. According to your reply, I have to save A10--A15, B10--B15

STW B3, *B15--[2]
STW B0, *B15--[2]
STW B14, *B15--[2]
STW B4, *B15--[2]

MV A4, in_data_ptr                                    ; short data pointer
MV A6, trans_sta_ptr 
MV B6, input_cnt
SUB input_cnt,1, input_cnt                     ; account for BDEC

.............

On spru187t.pdf, it says that B15 is preserved by Child. I don't know how to do it in assembly code because B15 itself is stack pointer. Is there other method to save it?

[quote]Please show me the C prototype for this assembly function.   [/quote] 

I don't know the above code snippet is your required. Thanks.