AWR2944: HWA FFTclip Register is always 11

Geogia

Part Number: AWR2944

Hi experts,

We want to monitor the HWA FFT data overflow, and found that after the DPU_DopProcHWA_process, the last two bits in the FFT_CLIP Register are 11, indicating that there is an overflow.

However, when we set the input data to 0 (memset 0 in decompSctrachBuf), it stands to reason that it will not overflow again, but the last two bits of the FFT_CLIP are still 11. I would like to ask you what is the reason for this?

over 1 year ago

0 Samhitha Bobba over 1 year ago

TI__Mastermind 19930 points

Hi Geogia,

You can perform FFT butterfly scaling to resolve this. If FFT size is N ( N>256) there is a chance that the FFT data could get clipped and saturate as the HWA bit-width still remains to be 24 bits. Eg: A 256 point FFT, can grow as much as 2^8 times the input. In terms of the HWA, the register bit width is 24 bits. Therefore, if there is no input scaling performed, the FFT output can grow all the way up to 24 bits after its 8 stages. (2^16 * 2^8 = 2^24).

Refer to AWR294x Technical Reference Manual (Rev. C) (ti.com) for more details.

Regards,

Samhitha

0 Geogia over 1 year ago in reply to Samhitha Bobba

Prodigy 170 points

Thank you for your reply. But in fact, my FFT size is 192, and I have already tried to set the butterflyScaling=1<<6-1, butterflyScalingFFT3X=2, and it will not change the 11 in FFTCLIP. As I said, I have already forced the input data to 0, why does saturation still appear?

0 Samhitha Bobba over 1 year ago in reply to Geogia

TI__Mastermind 19930 points

Hi Geogia,

Today is a holiday in India. I'll get back to you early next week.

Regards,

Samhitha

0 Samhitha Bobba over 1 year ago in reply to Geogia

TI__Mastermind 19930 points

Hi Geogia,

Did you apply butterfly scaling to all the stages?

Regards,

Samhitha

0 Geogia over 1 year ago in reply to Samhitha Bobba

Prodigy 170 points

I mentioned it before, I have already tried to set the butterflyScaling=1<<6-1, butterflyScalingFFT3X=2. Is this what you said about "apply butterfly scaling to all the stages"?

+1 Samhitha Bobba over 1 year ago in reply to Geogia

TI__Mastermind 19930 points

Hi Geogia,

I didn't understand what you meant by butterflyScaling=1<<6-1. So I am asking if you applied butterfly scaling to all the stages. Is it 1<<5?

Regards,

Samhitha

0 Geogia over 1 year ago in reply to Samhitha Bobba

Prodigy 170 points

1<<6-1 means the value is 63, which means I applied 6 stages butterfly scaling.

0 Samhitha Bobba over 1 year ago in reply to Geogia

TI__Mastermind 19930 points

Hi Geogia,

Is your issue resolved? If yes, how did you resolve it?

Regards,

Samhitha

0 Geogia over 1 year ago in reply to Samhitha Bobba

Prodigy 170 points

No, my issue is not resolved. That's why I am seeking your help here.

0 Samhitha Bobba over 1 year ago in reply to Geogia

TI__Mastermind 19930 points

Hi Geogia,

Thank you for the confirmation. I thought that the issue is resolved as you have marked it as resolved.

Can you please confirm if you have checked the FFTCLIP register after Rangeproc and if there is any clipping, did you clear it by writing to CLR_FFTCLIP register?

Regards,

Samhitha

0 Geogia over 1 year ago in reply to Samhitha Bobba

Prodigy 170 points

1.After Rangeproc, I have checked there is no clipping.

2.After Rangeproc, read and clear CLR_FFTCLIP register. Then after Dopplerproc, also read and clear CLR_FFTCLIP register. There is no clipping after Rangeproc, but clipping after Dopplerproc.

0 Samhitha Bobba over 1 year ago in reply to Geogia

TI__Mastermind 19930 points

Hi Geogia,

Create a unit test with the same paramset and check if you are seeing this issue. Also provide same input in both the cases.

Regards,

Samhitha

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AWR2944: HWA FFTclip Register is always 11