SN65DSI84: Test Pattern

Hey Michael,

Are you sure this datasheet is the correct one? It seem that the display in the datasheet is 1200x960. This may explain why the registers must be modified and flickering occurs sometime, as the timings are mismatched.

Hi,

yes i am sure that it is the right datasheet on page 2 it is mentioned that the display is a 1920x1200 display. 

As far as i know the display vendors describe in the timing settings only for one LVDS channel. The system is using a dual channel LVDS. 

Hey Michael,

Can you send a register dump when in the color bar is enabled but no video is showing?

It seems like the color bar is only coming out from one of the LVDS channels rather than both. But from the registers setting you have sent everything seems to be configured correctly for dual mode. Is this an issue that spans across multiple boards?

Hi,

here the register dumps. For the start with yocto 

This is the picture i got.

When i set the register 0x3C to 0x10 i got the following.

When reducing the resolution on register 0x20 and 0x21 to 960 i got the following picture.

This is the according register dump.

thanks michael

Hey Michael,

Thanks for the images and the register settings. I wanted to see the status of register 0xE5 (error register) when the color bar is failing. Are you able to send the register dump when the screen is blank? I'm looking into the register config as well.

In all cases the the error register 0xE5 is 0x00

Even when the device is flickering 0xE5 remains at 0? 

The flickering is most likely due to some timing mismatches or a jittery DSI clock. What is the frequency of the DSI clock you are using?

The reason the register must be modified for the color bar is due to channel A and channel B have the same setting in this mode. when they are programmed at 1920x1200 the channel are trying to output a stream of 3840x1200. This is why the screen is blank.

Hi,

yes even when it is flickering 0xe5 is zero. What I at the moment not understand is, why i have to modify the resolution register to activate the color bar. I have another 21" Display with a resolution of 1920x1080. Also as dual channel configuration. The resolution register is set to 1920. When i activate the color bar. The color bar is displayed. Why is this the case? 

Another topic i do not really can catch is the following. The values for the mipi dsi inside the imx8mm is calculated in the samsung-dsim.c based on the settings in the panel-simple.c of the display. The values for the display i have taken from the datasheet. But the display is only showing content when i manually reduce the register 0x34 at least be factor 4. Any idea where this comes from?

Hey Michael,

Michael Schweikart said:

I have another 21" Display with a resolution of 1920x1080. Also as dual channel configuration. The resolution register is set to 1920. When i activate the color bar. The color bar is displayed. Why is this the case? 

Does this second display flicker as well? 

Michael Schweikart said:

The values for the display i have taken from the datasheet. But the display is only showing content when i manually reduce the register 0x34 at least be factor 4. Any idea where this comes from?

There is nothing in the SN65DSi84 that would cause the horizontal back porch to be divided by 4. Have you tried an ABA swap with the device?

These behaviors are abnormal as the bridge should not require changes to the timing to function properly. The input and output timings should be 1:1. 

Hey Michael,

I'm closing this thread due to inactivity.