DM8148 Display Latency

nandish mj

Intellectual 420 points

Hello,

We are using DM8148 with DVRRDK_03.50.00.05. We are using the following pipeline,

Capture(720p@50) --> DEI & Resize --> SwOSD(DSP) --> Display (720x576).

With this pipeline we are seeing a latency of around 190msec.

In my prints says,

DISPLAY: SDDAC(SEC1): 12 fps, Latency (Min / Max) = ( 255 / 0 ), Callback Interval (Min / Max) = ( 255 / 0 ) !!!

Latency Min and Callback Interval Min numbers seems to be not convincing.

We are expecting around 100msec.

I have gone through the following links which suggest to implement display ISR which helps to improve 1fps (40msec), but still not close to as expected.

http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/t/282790

http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/717/p/249459/904005#904005

over 9 years ago

0 Margarita Gashova over 9 years ago

TI__Guru* 80190 points

Hello,

e2e.ti.com/.../224844

BR
Margarita

0 Brijesh Jadav over 9 years ago

TI__Guru**** 399120 points

Hi Nandish,

How are you measuring your latency of 190ms? You capture is at 50fps, so capture takes around 20ms, there could be at max 8ms latency introduced by the capture driver. Also display is 25fps, so single frame takes around 40ms. Display could have input queue, if we assume 2 frames, 80ms is introduced by display alone.

DEI and SWMs should not take mode 20ms, so total latency should not be more than 150ms..

How are you measuring this latency of 190ms?

Regards,

Brijesh

0 nandish mj over 9 years ago in reply to Brijesh Jadav

Intellectual 420 points

Hi Brijesh,
1. We used HD camera focusing stopwatch timer and a display and used a high speed shutter camera to take the snapshot. In the captured snapshot, we could find the difference to be around 290msec. Since the display alone introduces around 100msec, we assumed the display latency around 190msec.

2. Visually, when we move our hand we could see lots of delay in the display.

3. The message printed seems to be not convincing.
DISPLAY: SDDAC(SEC1): 12 fps, Latency (Min / Max) = ( 255 / 0 ), Callback Interval (Min / Max) = ( 255 / 0 ) !!!

0 Brijesh Jadav over 9 years ago in reply to nandish mj

TI__Guru**** 399120 points

Hi Nandish,
Can you try reducing the links and check which link is taking maximum time? Lets say just run capture + display and check the latency. It should be less than 100ms, this path itself requires to be optimized first. You could try reducing number of primed buffer in the display to 1.
Please note that there is a fps missmatch between capture and display, capture is 50fps and display 25 fps, so need to drop almost every alternate frame in the capture.
Regards,Brijesh

0 nandish mj over 9 years ago in reply to Brijesh Jadav

Intellectual 420 points

Hi Brijesh,

1. We integrated the dspling ISR patch from the below link and were able to achieve around 40msec.

http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/717/p/249459/904005#pi239031349=7&pi317334=3

2. Now the latency is around 150msec.

3. We checked the latency by disabling SwOSD, but no use.

Is there any other option to achieve another 40 to 50msec improvements?

0 Brijesh Jadav over 9 years ago in reply to nandish mj

TI__Guru**** 399120 points

What does DEI do in your link? Also are you setting up the input fps and output fps correctly in the SWMS?
It could be because of the fps missmatch between capture and display you are seeing this latency.. can you drop alternate frame in the capture and see how latency looks?
Also have you tried reducing primed buffers in the display?Regards,Brijesh

0 nandish mj over 9 years ago in reply to Brijesh Jadav

Intellectual 420 points

Hi Brijesh,

1. Below is our DEI settings,

RESIZE_WIDTH = 720

RESIZE_HEIGHT = 576

if(i == 1) //HD camera
{
deiPrm[i].enableDeiForceBypass = TRUE;
deiPrm[i].outScaleFactor[DEI_LINK_OUT_QUE_VIP_SC][0].scaleMode = DEI_SCALE_MODE_ABSOLUTE;
deiPrm[i].outScaleFactor[DEI_LINK_OUT_QUE_VIP_SC][0].absoluteResolution.outWidth = RESIZE_WIDTH;
deiPrm[i].outScaleFactor[DEI_LINK_OUT_QUE_VIP_SC][0].absoluteResolution.outHeight = RESIZE_HEIGHT;
}

As per the above settings, DEI is turned off.

2. Changed display fps in Vdis_params_init(),

//pContext->mosaicParams[i].outputFPS = 30; //old setting
pContext->mosaicParams[i].outputFPS = 25; //changed now

But still, no improvements in latency.

0 Brijesh Jadav over 9 years ago in reply to nandish mj

TI__Guru**** 399120 points

Hi Nandish,
150ms latency is just too much for capture -> DEI -> Display. It looks like somewhere buffers just pilling up or not getting released. can you press 'p' on the console to get the performance statistics? It can tell use fps for each link.
There is a was to drop frames in the capture link. there is an ioctl to set the frame drop in the capture link. You could try dropping alternate fields in the capture and check the output?
Rgds,Brijesh

0 nandish mj over 9 years ago in reply to Brijesh Jadav

Intellectual 420 points

Hi Brijesh,

1. I tried pressing 'p' on the console, didn't get to see anything happening. Can you please help me in understanding this mechanism. Is there any function expecting the keyword 'p'?

2. I changed the parameter in function CaptureLink_drvInstSetFrameSkip(), to skip the alternate frames. But, no improvements.