DM368 Slice Level Capture Driver

Derek Richardson

Hi, I've been asked to implement slice level data exchange for capture, encode, decode and display in order to minimize latency in the video processing pipeline. I'll start with capture and encode.

I found this link which describes some of the steps required to setup slice level transfers: http://processors.wiki.ti.com/index.php/DM36x_H.264_encoder_FAQ#How_to_use_DM36x_H.264_Encoder_Low_latency_call_back_APIs_for_achieving_slice_level_captue_and_encode.C2.A0.3F

The note says it assumes that slice level capture is already implemented in the capture driver.

My question is how to implement the slice level capture? What code do I need to modify to achieve this? Is there any documentation describing how to approach slice level capture?

Thanks alot

Derek

over 14 years ago

0 Yashwant Dutt over 14 years ago

TI__Genius 17215 points

Hi Derek,

Last I knew, slice level capture was not supported by DM36x linux driver. Let me again check and get back.

regards

Yashwant

0 Derek Richardson over 14 years ago in reply to Yashwant Dutt

Intellectual 610 points

Yashwant, thanks

By not supported, do you mean not possible?

I found this thread: http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/100/t/63487.aspx#228379 which talks about a possible solution to implementing slice based capture. It talks about using the 3 VDINT interrupts, plus the resizer EOF to indicate end of frame, so slicing the frame into 4, which means 8.33ms slices for 30fps. I'm not sure though if this solution synchronizes well to the sliced based encoding scheme as described in the link I provided in my previous post.

This link: http://processors.wiki.ti.com/index.php/H.264_DM36x_Ver_2.0_Codec#Low_latency_API_and_fixed_packet_size_support says that with slicing, latency of the codec is reduced from 33ms to <2ms. I assume this is achieved by slicing the frame into something much greater than 4 parts, more like 16-20 slices. If it's not possible to slice more than 4 times, then my guess is that <2ms codec latency is not possible.

Any insights into the sliced based capture would be greatly appreciated!

Thanks alot

Derek

0 Manjunath Hadli56783 over 14 years ago in reply to Derek Richardson

TI__Prodigy 650 points

Slice based support on DM36X is not supported. It could be done in the way some of the posts suggest . Like Kedar explains, the VDINT support is provided to give interrupts after X lines from the START and not the LAST SLICE END. this being the case, the whole frame can be broken into a max of 4 parts. The codec example talks of a 2MB buffer but not how many lines. If the slice size is lesser than 1/4 of the height of the capture buffer, the capture device cannot be made to support the slicing.

-Manju

0 Derek Richardson over 14 years ago in reply to Manjunath Hadli56783

Intellectual 610 points

Hi thanks Manju,

Just to clarify, "not supported" means there are no provisions in the DM36X software libraries for implementing sliced based capture, however, if I make appropriate modifications to the capture driver source code as Kedar describes, I can, at best, achieve a 4 part slicing. Is my understanding here correct?

Thanks

Derek

0 Manjunath Hadli56783 over 14 years ago in reply to Derek Richardson

TI__Prodigy 650 points

Yes. That is correct.

-Manju

0 Derek Richardson over 14 years ago in reply to Manjunath Hadli56783

Intellectual 610 points

Great, thanks alot for your help! Much appreciated

Cheers

Derek

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DM368 Slice Level Capture Driver