AddData block in Purepath (miniDSP, TLV320AIC3253): overflow mode not working as expected

Filip Zalio

Other Parts Discussed in Thread: TLV320AIC3253EVM-K, TLV320AIC3254EVM-K

Hi,

I am experimenting with the math. I have the following flow running on the TLV320AIC3253EVM-K. The left channel outputs a sinewave, which proves that I have my system setup correctly. I would expect that the right channel would show a saw tooth. Or maybe an inverted saw tooth?

I am getting this waveform:

Would anyone be able to help with debugging this? What are the data types?

Thank you.

-- Filip

over 9 years ago

0 Filip Zalio over 9 years ago

Prodigy 70 points

Additional information:

- the constant in the C_to_D_1 block is set to 0.01.

- the AddData_1 block has OverflowMode set to "wrap".

- the delay in the delay block is set to 1.

0 Luis Fernando Rodriguez S. over 9 years ago in reply to Filip Zalio

TI__Guru* 84915 points

Hi, Filip,

I'm using the TLV320AIC3254EVM-K. I obtained a different result.

I attached the process flow for details.

ProcessFlow1.zip

Best regards,
Luis Fernando Rodríguez S.

0 Filip Zalio over 9 years ago in reply to Luis Fernando Rodriguez S.

Prodigy 70 points

I since realised what the issue was: The output of the "Adddata" block is 3.29 format. Not sure if this means it's 32 bits in total. Anyway, the DAC has a smaller bit width at its input. So, the data is getting truncated, and we see a clipped saw tooth, rather than the expected complete saw tooth. I fixed it by right-shifting the Adddata output . TI has not documented this anywhere as far as I can tell, which seems like an omission.

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AddData block in Purepath (miniDSP, TLV320AIC3253): overflow mode not working as expected