Mixing asm and C on C6474

The compiler's assembly output will show you how to write the function to accept the arguments and to return the arguments, and also how to handle the rest of the control of the function. You do not have to use the math contents of the compiler's assembly output, but you can learn from the compiler's techniques.

Also, you need to learn to use the CCS debugger if you plan to write assembly code. Using printf's for debugging assembly makes your job that much harder.

And writing the function in C first will also allow you to test your C testbench to find out what else you need to modify.

Here is my testbench C code:

#include <stdio.h>

long long fastmul(long long a,long long b);

void main()
{
    long long x = 0;
    long long a          = 0x01aaaaaabbbbbbbbLL;
    unsigned long long b = 0x02ccccccddddddddULL;
//    printf("a: %lld, b: %llu\n", a, b);
   
    x = fastmul( a, b );
}

Here is my testbench asm code:

    .global _fastmul

_fastmul:
        mvkl    0x03eeeeee, a5
        mvkh    0x03eeeeee, a5
        mvkl    0xffffffff, a4
        mvkh    0xffffffff, a4

        B        B3
        NOP        5

In CCS, I can see in the Core Registers display window that when I enter _fastmul, the correct registers are loaded as expected for the parameters passed through the function argument list. And I can see that after completing the assignment to x in main() the correct value is loaded into x.

Finally, you need to search the TI Wiki Pages for C6000 Optimization and study the Wiki topics and the workshop material. It would be best to take a class in C6000 optimization, but that may not be likely. Other than for trivial examples like my C code above, I always start with the C version, keep the assembly, strip it down to the parts I need, then start optimizing from there. Your code needs further optimization, as does mine above.

Regards,
RandyP

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