Long execution time using dsp 28335

Milarepa

Expert 1670 points

I am running a motor through an inverter.

My main code which is inside taking 130 us, which is too much for a small piece of code.

My switching frequency is currently 5kHz (T=200 us). If I use 10kHz, then I am getting erroneous results.

Epwm settings related to switching frequency are:

Regards

over 8 years ago

0 Gautam Iyer over 8 years ago

Guru 192875 points

Hi Shyam,

shyam nair said:
My main code which is inside interrupt void epwm1_isr(void) taking 130 us, which is too much for a small piece of code.

In short you'll have to do the 130us computations in a more optimized way to squeeze the same in 100us. This is what you're looking for right?

Can you be more specific on what you're seeking for?

Regards,

Gautam

0 Milarepa over 8 years ago in reply to Gautam Iyer

Expert 1670 points

No, Actually, that small piece of code should not take 130us.There is some error in settings or somewhere, which I am not able to figure out.
I am toggling a GPIO pin and found the execution time to be 130us for that part under epwm1 isr.
My switching frequency is 5kHz, which I have verified.

0 Janos Szeman over 8 years ago in reply to Milarepa

Intellectual 985 points

Hi,

Could you please share the code for the ISR?

J

0 Milarepa over 8 years ago in reply to Janos Szeman

Expert 1670 points

code

0 Janos Szeman over 8 years ago in reply to Milarepa

Intellectual 985 points

I did not do the calculations, but it looks like you set up the ADC to a slow conversion speed (low noise). You start the conversion inside the ISR and busy wait for the result. So, my bet is on the adc_example() function.

0 Milarepa over 8 years ago in reply to Janos Szeman

Expert 1670 points

Thanks for ur reponse.
I checked the execution time for adcexample()...its not much.
I am using rts2800.lib, which is a fixed point lib. I am doing floating point calc using fixed point lib. I am thinking thats the issue.
I am using CCSV3.3 and fpu32lib does not seem to be compatible with V3.3.

0 Gautam Iyer over 8 years ago in reply to Milarepa

Guru 192875 points

As far as I can see you're doing multiplication operation in ePWM isr, right?
EPwm1Regs.CMPA.half.CMPA =(1+VA)*7500*2*0.5;
EPwm2Regs.CMPA.half.CMPA =(1+VB)*7500*2*0.5;
EPwm3Regs.CMPA.half.CMPA =(1+VC)*7500*2*0.5;

The above 3 statements have 3 multiplication operations in a single statement! You can check the timing by commenting out the multiplications.

Regards,
Gautam

0 Milarepa over 8 years ago in reply to Gautam Iyer

Expert 1670 points

I haven't shown the full code. There are many multiplications like the one above.
Are u saying problem is in using rts2800.lib.

0 Gautam Iyer over 8 years ago in reply to Milarepa

Guru 192875 points

I mean to say, these computations are consuming lot of time which I want you to check by commenting and then toggling GPIO. Let me know what you observe.

0 Milarepa over 8 years ago in reply to Gautam Iyer

Expert 1670 points

Those 3 lines involving multiplication are taking 11us.

0 Gautam Iyer over 8 years ago in reply to Milarepa

Guru 192875 points

Ahhhh... now that 2 parts of the ISR are eliminated. What is the part that is consuming the maximum time?

Regards,
Gautam

0 Milarepa over 8 years ago in reply to Gautam Iyer

Expert 1670 points

Actually, isr part has many multiplications. I have shown only some lines here and there arbitrarily.
Do u suggest moving to CCS6 and using fpu32lib?

I dont want to use IQmath.

Thanks a lot

0 Gautam Iyer over 8 years ago in reply to Milarepa

Guru 192875 points

shyam nair said:
Do u suggest moving to CCS6 and using fpu32lib?

FPU32 should be automatically selected. Check your project properties for the same, here's an example:

0 Milarepa over 8 years ago in reply to Gautam Iyer

Expert 1670 points

Ok..fpu32 is not working with ccsv3.3...I think what u hav shown is ccs6?
Thanks

0 Gautam Iyer over 8 years ago in reply to Milarepa

Guru 192875 points

Yes. Its in 6.

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Long execution time using dsp 28335