Low_latency_mode question

[miaofeiyu1991]

We use TX2-NX board on version 32.7.2

We are using an ISX019,10fps camera, but due to hardware reasons, when we use a trigger signal, we will lose 3-5 frames

When we use the regular v4l2 command like this
v4l2-ctl --set-ctrl --set-ctrl bypass_mode=0 --stream-mmap -d /dev/video0

result is that：

<<<<<<<<<< 10fps
<<<<<<<< 9fps （sync signal）
<<<<<<< 8fps
<<<<<<<<<< 9fps

This is in line with our expectations,

But we encountered two difficult to explain phenomena

1. When we use low_latency_mode, once a trigger signal is generated, the application will block

When using the following v4l2 command
v4l2-ctl --set-ctrl low_latency_mode=1 --set-ctrl bypass_mode=0 --stream-mmap -d /dev/video0

result is that：

<<<<<<<<<< 10fps
<<<<<<<<<< 10fps
<<<<< （sync signal）

The application is blocking here

dmesg continuously displays the following information

tgra-vi4 15700000.vi: PXL_SOF syncpt timeout! err = -11
tgra-vi4 15700000.vi: PXL_SOF syncpt timeout! err = -11
tgra-vi4 15700000.vi: PXL_SOF syncpt timeout! err = -11
tgra-vi4 15700000.vi: ATMOP_FE syncpy timeout! err = -11
tgra-vi4 15700000.vi: PXL_SOF syncpt timeout! err = -11
…

2. This is an occasional issue, and sometimes, after the trigger signal is generated, the following situations occur, and the frame rate seems to have decreased by half

v4l2-ctl --set-ctrl --set-ctrl bypass_mode=0 --stream-mmap -d /dev/video0

result is that：

<<<<<<<<<< 10fps
<<<<<<<<<< 10fps
<<<<< 8fps （sync signal）
<<<< 8fps
…
<<<<< 5fps
<<<< 5fps

This is clearly missing a lot of frames

dmesg continuously displays the following information

tgra-vi4 15700000.vi: PXL_SOF syncpt timeout! err = -11
tgra-vi4 15700000.vi: PXL_SOF syncpt timeout! err = -11
tgra-vi4 15700000.vi: PXL_SOF syncpt timeout! err = -11
tgra-vi4 15700000.vi: ATMOP_FE syncpy timeout! err = -11
tgra-vi4 15700000.vi: PXL_SOF syncpt timeout! err = -11
…

In addition:

In both cases, we can observe a mipi signal of 10 frames per second using an oscilloscope

And even if we don’t perform any operations on the camera, we only turn on dev/video0 again (we have turned off all operations in the sensor driver), and the camera can still function normally again

[ShaneCCC]

Increase the timeout in the vi4_fops.c to verify.

chan->timeout = msecs_to_jiffies(200);

[ShaneCCC]

Please use below command to check the timestamp.

v4l2-ctl --stream-mmap --verbose