Screen rotation issue with BT817 on 1280x800

[Rudolph]

I am using a RVT101HVBNWC00-B from Riverdi which is a BT817 with a 1280x800 panel.
And to rotate the screen does not work properly, just flipping it with either REG_ROTATE set to 1 or using CMD_SETROTATE(1) causes major distortion.

When I use CMD_SETROTATE(5) it curiously works fine though, I have no use for a mirrored image though.

0 - image is fine, just for reference
1 - image is distorted
2 - image is fine
3 - image is distorted
4 - image is distorted
5 - image is fine
6 - image is fine
7 - image is distorted

And right now it does not have to display much at all, it looks like this with more empty pixels:
https://github.com/RudolphRiedel/FT800-FT813/blob/5.x/example_pics/CFAF800480E0_050SC_Arduino_Uno.jpg

Pixelclock is 72MHz with REG_PCLK_2X set to 1.

Hmm, I dropped the pixel clock to 51MHz with REG_PCLK_2X set to 0 and now the flipped image is fine.
But this dropped the frames/s as well and the pixel-clock is now well below the minimum of 66.3MHz that is listed in the datasheet.

I set REG_PCLK_2X to 1 while still using 51Mhz -> image is distorted when flipped.
I set REG_PCLK_2X to 0 while using 72MHz -> image is fine.
I set REG_PCLK_2X to 0 while using 66MHz -> image is fine.

Any more advice on this why REG_PCLK_2X = 1 with REG_ROTATE = 1 leads to a distorted image?

At 72MHz pixel-clock with 72Mhz system clock the datasheet says that REG_PCLK_2X needs to be set to 1.
And 66MHz is out of spec for the panel, although barely, it is not possible though to set PLL2 to anything between 66MHz and 72MHz.

I reduced the pixel clock to 38MHz and it still works, here at my desk.
But there is no way to tell what will happen out in the field with -20°C....+60°C.

[BRT Community]

Hi Rudolph,

Are you seeing REG_UNDERRUN count up in the cases where you see the issue?

Best Regards, BRT Community

[Rudolph]

I am reading REG_UNDERRUN now and it just sits at zero.

And it should be as there is hardly anything to display, yet.
The external flash is also not in use.
Also tried my current playground app which puts significantly more stress on the pixel engine,
does not change though that the value for REG_UNDERRUN is printed out as zero.
Well, untill it crashes for good but there is a good chance that this is my software. :-)

I just tried using 78MHz pixel clock which is below the maximum for the panel.
And with REG_PCLK_2X set the distortion is the same.
But without setting REG_PCLK_2X it is rather unstable.

Using 66MHz without setting REG_PCLK_2X might be my only option, at least this is almost within spec.
And the drop to 54.7Hz is ok as well, I hope.