TMS320F28377S: Different timing for multiply instruction in structure

Johnny Chen

Expert 5140 points

Part Number: TMS320F28377S

Hi Champ,

I am asking for customer.

In C language, the operation of a ->b and (*a).b are the same meaning in structure in my understanding.

The customer has found the time consumption for processing two instructions, there is a gap.

In the function, the writing like this way, MathTemp = (f32)ADC * Gain_Matrix->Low_Gain, have all changed to the following way, MathTemp = (f32)ADC * (*Gain_Matrix). Low_Gain.

It is tested the time consumption reduces significantly to 3 us after modified. (a ->b to (*a).b )

The two meanings should be the same, but the result is quite different.

I would like to ask this kind of operation (especially the one with ->), is it not recommended to use in the CCS?

Why makes them different ? Did it make a mistake of using ?

May I clarify the use of the multiply instruction in structure between a ->b and (*a).b ?

Thanks.

BR, Johnny

over 4 years ago

0 Chester Gillon over 4 years ago

Guru 92251 points

Johnny Chen said:
The two meanings should be the same, but the result is quite different.

Agreed.

Can the customer follow How to Submit a Compiler Test Case?

0 Ashwini Athalye over 4 years ago

TI__Expert 7715 points

Hi Johnny,

The meaning is the same you are correct, but it may be that the two different C usages is resulting in different assembly code. It would help if you could send the following for our analysis:

1. Submit a test case using How-to-Submit-a-Compiler-Test-Case.html.

2. Compiler version

3. Compiler optimization level

4. Definition of structure "a"

Thanks,

Ashwini

0 Ashwini Athalye over 4 years ago in reply to Chester Gillon

TI__Expert 7715 points

Chester, Thanks for the reply.

0 Johnny Chen over 4 years ago in reply to Ashwini Athalye

TI__Expert 5140 points

Hi Chester and Ashwini,

Thank both of you. I see, the time consumption maybe the two different C usages is resulting in different assembly code.

I would ask my customer to provide the need as you said for your analysis.

But, thank you in advance.

Johnny

0 Ashwini Athalye over 4 years ago in reply to Johnny Chen

TI__Expert 7715 points

Hi Johnny,

Thank you, we will be happy to investigate once we have the details.

-Ashwini

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TMS320F28377S: Different timing for multiply instruction in structure