TMS320F28377D: Dual MAC Required Build Options

Hi George,

Thanks for your reply!  This is a good solution, I will give you feedback after trying it!

Hi George,

As you said, I used  an intrinsic named __dmac. In the performance comparison, I wrote the code as follows：

• for (i = 0; i < 3; i++)
  {__dmac(p1_32[i], p2_32[i], acc1, acc2, 0);}

• for (i = 0; i < 3; i++)
  {re2 += (int32_t) p1_32[i] * p2_32[i];}

I used 28388 for testing and found that both of them took 76 cycles. I check the assembly instructions, the latter does not generate DMAC instructions. That is, the result cannot explain the efficiency of DMAC, please help!

A DMAC instruction by itself offers little improvement.  To get the improvement you expect, the surrounding code, especially the loop control, must be optimized too.  You want the compiler to ultimately generate something similar to ...

        RPT       AR5
||      DMAC      ACC:P,*XAR4++,*XAR7++
        ADDL      P,ACC

Because of this constraint ...

Bruce(Shanghai) Liu said:

the customer is unwilling to increase the optimization level(--opt_level ==0)

... the compiler will never generate that code.  Generating that code requires, among other things, use of --opt_level=2 or higher.

Thanks and regards,

-George

Fine...Recently, customer accepted to modify the optimization level of a single function. However, they encountered a new problem. when they use #pragma FUNCTION_OPTIONS(func , " --opt_level=2") to increase function's optimization level, They found that the calculation time of the function hardly decreased. 

It is worth mentioning that many loop operations and ternary operators are used in this function. I have asked customers to observe the assembly code, but there is no reply yet. What are the possible reasons for this result?

For this ...

Bruce(Shanghai) Liu said:

#pragma FUNCTION_OPTIONS(func , " --opt_level=2")

... to work, you have to compile with at least --opt_level=0.

In addition, please be sure you are taking all the steps described in pages 25-30 of the C28x optimization presentation available in the article TI Compiler Presentations.

Thanks and regards,

-George

Thanks for reply!

 The project are compiled with --opt_level=0 now. Optimizer Assistant is a good tool, I will try to use it.

So George, back to the first question, when I compile with --opt_level=3, the C code is as follow:

int32_t a[6]={1,2,3,4,5,6};
int32_t b[6]={1,2,3,4,5,6};

long res = 0;
long temp = 0;
for (i=0; i < 3; i++) // N does not have to be a known constant
__dmac(((long *)a)[i], ((long *)b)[i], res, temp, 0);
res += temp;

The generated assembly code is as follows：

So why I cannot generate assembly code as follow even if I compile with --opt_level=3

RPT AR5

DMAC ACC:P,*XAR4++,*XAR7++
ADDL P,ACC

Unfortunately, I am unable to generate the same code you do.  I must be doing something different.  To be sure I am doing everything the same, for the source file which contains the DMAC loop, please follow the directions in the article How to Submit a Compiler Test Case.

Thanks and regards,

-George

Hi George,

I follow  the directions in the article How to Submit a Compiler Test Case, but I still cannot generate the desired assembly code. I attach my compiler configuration, please help and give some suggestions

If everything seems ok, you can attach your code sample so that I can refer to it. Thanks！

Bruce(Shanghai) Liu said:

I follow  the directions in the article How to Submit a Compiler Test Case, but I still cannot generate the desired assembly code.

I apologize.  The point of the article was for you to prepare a test case you submit to me.  Then I would use that test case to reproduce your results.  Once I can do that, I can probably tell you the changes to make to generate the faster code I see.  

So, please follow the directions in that article so that I have a the code, and other details, that allow me to reproduce your results.

Thanks and regards,

-George

"C:/ti/ccs1040/ccs/tools/compiler/ti-cgt-c2000_20.2.5.LTS/bin/cl2000" -v28 -ml -mt --cla_support=cla2 --float_support=fpu64 --idiv_support=idiv0 --tmu_support=tmu0 --vcu_support=vcrc -O2 --opt_for_speed=5 --fp_mode=relaxed --include_path="C:/Users/a0488871/workspace_v10/empty_driverlib_project" --include_path="C:/Users/a0488871/workspace_v10/empty_driverlib_project/device" --include_path="C:/ti/c2000/C2000Ware_3_04_00_00/driverlib/f2838x/driverlib" --include_path="C:/ti/ccs1040/ccs/tools/compiler/ti-cgt-c2000_20.2.5.LTS/include" --define=DEBUG --define=CPU1 --preproc_with_comment --preproc_with_compile --diag_suppress=10063 --diag_warning=225 --diag_wrap=off --display_error_number --gen_func_subsections=on --abi=eabi --include_path="C:/Users/a0488871/workspace_v10/empty_driverlib_project/CPU1_RAM/syscfg" "../empty_driverlib_main.c"

compiler version=  20.2.5.LTS

To see how this got resolved, please visit this forum thread.

Thanks and regards,

-George