TMS320C6747: PING PONG buffer delay

Jagdish Patange

Part Number: TMS320C6747

Sir/madam,

I am using Codec AIC3106 and ADC6140 interfaced DSP TMS320C6747 via McAsp1 and McAsp0 ports.

Codec or ADC samples are read/written using EDMA peripheral. EDMA will generate interrupt after collecting/sending one frame of data i.e. 32 samples @16k Sampling rate i.e. frame duration is 2 msec.

I am using PING PONG buffer concept, hence I expect total absolute delay of 4 msec between audio input to audio output.

0th instant--> PING buffer is filled

2msec-->PING buffer processed and PONG buffer filled

4msec-->PING buffer filled and PONG buffer processed.

But, when I measured, I am getting absolute delay of 6.5 msec. This additional 2.5 msec delay is not understood. Please explain?

Measurement method.

Input: AM modulation with 50 Hz modulating input and 1 kHz carrier input and 90% modulation depth.

Difference between input peak to output peak is measured.

Snapshot of measurement is attached

over 2 years ago

0 Suren Porwar over 2 years ago

TI__Mastermind 31440 points

Hi Jagdish,

I have assigned this query to our expert. In the meantime, do look at the below thread and see if it helps.

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/436726/edma-mcasp-ping-pong-buffer-read-problems

Also, if you refer section 16.3.4.4 on Ping Pong buffering in the TRM (SPRUH91D) https://www.ti.com/lit/pdf/spruh91

Hope these help.

Best Regards,

Suren

0 Jagdish Patange over 2 years ago in reply to Suren Porwar

Intellectual 290 points

Hi Suren,

I have checked the thread which talks about EDMA access. For me, EDMA and McAsp are working fine. Only concern is, expected absolute delay is 4 msec but actually measured is 6.5 msec.

Is it that codec AIC3106 or ADC6140 introduces this delay while applying internal decimation? If it is so, can it be reduced?

What has caused this additional delay of 2.5 msec. Awaiting for Reply.

0 Jagdish Patange over 2 years ago in reply to Jagdish Patange

Intellectual 290 points

Hi Suren,

in AIC3106 datasheet, it is mentioned that Group delay for Decimation filter is 17/fs and interpolation is 21/fs.

if fs is 16k then, 2.375 msec is the total group delay. I feel this is the additional delay which I am getting.

Am I right?

0 Suren Porwar over 2 years ago in reply to Jagdish Patange

TI__Mastermind 31440 points

Hi Jagdish,

I am forwarding your query regarding Audio codec to the codec expert. If you don't get to hear from them in a day or two, reach out to me for further assistance.

Best Regards,

Suren

0 Shenghao Ding over 2 years ago

TI__Genius 12320 points

Hi,

Have you check whether the time consumption of the procession is always a stable value or fluctuation?

if it is the fluctuation, you need add more buffers to create a circular queue instead of PING-Pong buffer to smooth up fluctuation.

0 Jagdish Patange over 2 years ago in reply to Shenghao Ding

Intellectual 290 points

My processing time varies between 0.6 ms to 1.5 ms. Frame length is 2 ms, hence processor is always read to process new buffer in real time. This absolute delay is always fixed, even if remove processing and simply copy input buffer to output still this delay is fixed.

Is, codec adding the delay? please explain.