DS90UB954-Q1: TI FPD-link serdes question

Hello Feng,

Timing is very important in synchronization. 

"The forwarding engine attempts to send the video synchronized. If synchronization fails, the CSI-2 transmitter stops forwarding packets and attempts to restart sending synchronized video at the next FrameStart indication. Packets are discarded as long as the forwarding engine is unable to send the synchronized video."

I am understanding that the "correct" picture you send, is composed of video data from sensor A and B. 

What is the third portion (upper half of the "fail" picture)? Which sensor is that coming from?

What do you mean by, " If Image source output timing is slightly bouncing?"

Best Regards,

Shruti

Hi Shruti,

We're thinking about if the deserializer output data may not in the order SA-SB.

The corect picture is the image of IMX390, the image is deinterleaved.

The wrong picture upper half is from OV2778, the other is the image of IMX390, please check the hardware diagram.

We need to know is there a chance that the imx8mp receives the data not in the order SA-SB.

Please also check the video at 25 and 37 seconds.

Thanks.

Chris Liu.

Hello Chris,

I don't think there is an issue with DES outputs (SA-SB-SA-SB).

There might be a synchronization issue. Please refer to section "7.5.10 Timestamp - Video Skew Detection." "The skew detection can run in either a FrameSync mode or free-run mode. Skew detection can be individually enabled for each RX port.

Before reading timestamps, the TS_FREEZE bit for each port that will be read should be set. This will prevent overwrite of the timestamps by the detection circuit until all timestamps have been read. The freeze condition will be released automatically once all frozen timestamps have been read. 

Please check register TS_STATUS (0x29).

Best Regards,

Shruti

Hi Shruti,

We know there may have synchronization issue, what we want to know is: if there is synchronization issue occur, will the DES output incorrect or incomplete frame?

We have done some long time testing and found that there're some frame incorrect. Each incorrect frame are coupled, it means imx390 and ov2778 have the same incorrect frame at the same time, the same incorrcet format.

I guess in the frame begining, the synchronization is ok, after some lines the synchronization failed, the imx8mp just recieved some lines int the beginning of frame.

Please check the below picture, all the incorrcet frame like that.

Hello Chris,

No, if there is synchronization issue, the DES will not output incorrect or incomplete frames. If synchronization fails, the DES "stops forwarding packets and attempts to restart sending synchronized video at the next FrameStart indication. Packets are discarded as long as the forwarding engine is unable to send the synchronized video."

FS_A – SA_L1 – SB_L1 – SA_L2 – SB_L2 – SA_L3 … . . .  SA_LN – SB_LN – FE_A 

If a sync failure occurs in the middle, the DES stops and restarts sending data at the next frame start.

You can also check frame sync error with register 0x22[2]

It could be that the SoC might not be understanding how to process the video after a synchronization failure and that is why you might be seeing those images on the screen.

Best Regards,

Shruti

Hi Shruti,

Thanks for your explanation.

I think the main problem is sync failure occurs in the middle, so I have a question, if a sync failure occurs in the middle, will the DES send FE_A?

Hello Chris,

No, the DES does not send FE_A.

Best Regards,

Shruti

Hi Shruti,

Thanks for the quick reply.

GEO ISP vendor has a question, for synchronization, for 1920x1080, 30fps image, the line period is about 1/1080/30 = 30 us, isn't it?

Hello Chris,

The line period would based on the Vtotal, not just the Vactive. 

So line period = 1/(Vtotal x fps)

Best Regards,

Shruti