DS90UB960-Q1: Line-Concatenated CSI-2 Forwarding mode got CSI-2 Sync Error

user4289837

Part Number: DS90UB960-Q1

Hello

I'm using 960 with two 913 in Line-Concatenated CSI-2 Forwarding mode. Sometime we can get the correct video .But sometime,we saw synchronization errors in 960(Register (Address 0x37) = 0x0c) ,and we only got a video with frame rate about 27、28.

the resolution of the sensor working with 913 is 1280x720 ,data type is RAW10;

Two sensors are synchronizied by a framesync signal generated by 960.

below are the two framesync signals output by two 913.

one HSync is faster than another about 340 ns . 340ns is much shorter than one line's time(37us)

So I'm not sure that 340ns is a acceptable delay? if yes ,than why I still got sync error occasionally？

Two VSync signals , still 340ns delay

Best Regards

NickLi

over 4 years ago

0 Jiashow Ho over 4 years ago

TI__Genius 11340 points

Hi Nick,

Could you re-attach the picture?

The start of the frame needs to be within the video line time. Sync error refers that the videos are not synchronized enough, or possible there's drift over time causing the videos to go out of sync.

Best,

Jiashow

0 user4289837 over 4 years ago in reply to Jiashow Ho

Intellectual 435 points

Hi Jiashow

the two framesync signals are almost the same.

Here are the two Vsync signals， 340ns delay

0 user4289837 over 4 years ago in reply to user4289837

Intellectual 435 points

Hello，Jiashow

Here are the two Vsync in 1s. It's just 30fps , but 960 still got sync error. Any other reason?

Nick Li

0 Jiashow Ho over 4 years ago in reply to user4289837

TI__Genius 11340 points

Hi Nick,

What's your video line time? You can measure it or calculate it using the equation: Video Line Time= 1 / PCLK * Horizontal Resolution in Pixels

You will need to make sure your videos come in within the video line time.

Best,

Jiashow

0 user4289837 over 4 years ago in reply to Jiashow Ho

Intellectual 435 points

Hello, Jiashow

Two HSync as below

After expanding the axis ，we can see that one video came after another about 340ns as below . And this is the first line of the first frame

0 Jiashow Ho over 4 years ago in reply to user4289837

TI__Genius 11340 points

Hi Nick,

It's sill unclear what the video line time is based on the scope shots. What's your PCLK and horizontal resolution?

Also, are the imagers identical? What type of forwarding method are you using?

Best,

Jiashow

0 user4289837 over 4 years ago in reply to Jiashow Ho

Intellectual 435 points

Hi Jiashow

PCLK ：45MHz

Resolution：1280x720

Two imagers are identical, and were syncronized by a framsync signal

We are using line-concatenated CSI-2 Forwarding mode

0 Jiashow Ho over 4 years ago in reply to user4289837

TI__Genius 11340 points

Hi Nick,

Based on the parameters you gave, the line time is 28ms. A 340ns delay should not cause any sync issues.

The 340 is the delay between the start of the frames right? Are you seeing any other issues?

Jiashow

0 user4289837 over 4 years ago in reply to Jiashow Ho

Intellectual 435 points

Hi Jiashow

The 340ns is the delay between the start of the frames， Yes，and as the two frames are identical . every delay between the start of the lines is 340ns too.

Didn't see any other issue , Only the host detected a mipi error ,that there was frame lost, while 960 Register (Address 0x37) = 0x0c

Best regards

Nick Li

0 Jiashow Ho over 4 years ago in reply to user4289837

TI__Genius 11340 points

Hi Nick,

Did you set all the virtual channel IDs to 0? In line concatenation mode, the VC IDs all need to be 0.

Best,

Jiashow

0 user4289837 over 4 years ago in reply to Jiashow Ho

Intellectual 435 points

Hi Jiashow

Yes ， Both VC ID are 0. And host can get the right video except frame lost sometimes .

Below is the video

Best regards

Nick Li

0 Jiashow Ho over 4 years ago in reply to user4289837

TI__Genius 11340 points

Hi Nick,

Regarding frame lost, there are two likely possibilities:

1. The imagers doesn't output the frames (or outputs frames with errors). I would suggest checking the imager output

2. There's drift over time which causes the imagers to go out of sync. Check the scopeshots when frames are lost.

Best,

Jiashow

0 user4289837 over 4 years ago in reply to Jiashow Ho

Intellectual 435 points

Hi Jiashow

Below is the imager vsync output when frames are lost， didn't see any frames lost and drift. And here‘s another information，after power up. If host get the right video at 30Hz, it will be right all along , but if host get the wrong video (like 27Hz or 28Hz), it will kept losing frames all along. After checking the imager's output , we didn't see any difference between imager's outputs when host get right or wrong video.

Best regards

Nick Li

0 Jiashow Ho over 4 years ago in reply to user4289837

TI__Genius 11340 points

Hi Nick,

Why would the CSI frame rate between different at start up? Is the clock to the imager not stable?

Jiashow

0 user4289837 over 4 years ago in reply to Jiashow Ho

Intellectual 435 points

Hi Jiashow

The clock to the imager is stable，After start up， the output of the imagers is stable and synchronized，frame rate is always 30Hz.

It's just some times, 960 didn't work correctly and we saw synchronization errors in 960(Register (Address 0x37) = 0x0c), at this time ,the frame rate of 960's output will not be 30Hz

best regards

Nick Li

0 Jiashow Ho over 4 years ago in reply to user4289837

TI__Genius 11340 points

Hi Nick,

Based on my understanding, the frame rate of 960 output is unstable only when there's sync errors. When the frame rate is unstable, is the input frame rate to the serializer stable?

0 user4289837 over 4 years ago in reply to Jiashow Ho

Intellectual 435 points

Hi Jiashow

When the frame rate is unstable, the input frame rate to the serializer is stable and 30Hz.Below are the two inputs

Best regards

Nick Li

0 Jiashow Ho over 4 years ago in reply to user4289837

TI__Genius 11340 points

Hi Nick,

If the input is always stable, the only other reason I can think of is that there's drift in the two input cameras over time. I believe if you simply use best effort round robin forwarding, the CSI data can be processed without issues.

Best,

Jiashow

Interface

Interface forum

DS90UB960-Q1: Line-Concatenated CSI-2 Forwarding mode got CSI-2 Sync Error