Working KMS image with newest RetroPie on Pi 4? Help with config with VGA666?

[phos]

Hello,

I have a working install of RetroPie that has been updated to 4.7.7 and has been updated over SSH using rpi-update.

I am using a Pi 4 with VGA666 with a RGB-composite converter box to a consumer CRT which is providing a very clean 240p image whenever still.

240p test suite (Mega Drive) reveals subtle but annoying juddering when scrolling. The image is not actually tearing though, it appears more like a slight hitch or shake on scrolling elements.

I am using a 1:1 PAR in Retroarch at 320x240 and I have tried every video option available. Turning VSYNC off makes the juddering slightly worse. Everything else makes no difference or causes frame rate issues.

My idea was to try the KMS driver to fix this issue but I haven't gotten it to boot Emulation Station. Trying to boot ES over SSH gives me "error creating SDL window".

Here is my config:

# Turn off conflicting peripheral overlays using GPIO pins.
dtparam=i2c_arm=off
dtparam=spi=off
dtparam=i2s=off
enable_uart=0

# Set default display.
dtoverlay=vga666
enable_dpi_lcd=1
display_default_lcd=1

# Enable custom dpi timings.
dpi_group=2
dpi_mode=87

# Set custom dpi timings.
dpi_timings=320 1 23 25 39 240 1 4 3 15 1 0 0 60 0 6400000 1

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
#  dtoverlay=vc4-fkms-v3d
dtoverlay=vc4-kms-v3d-pi4
max_framebuffers=2

Any suggestions? Does anyone simply have a working IMG of a base install with working KMS? Would be very helpful as the juddering makes this system unplayable. If I could just solve the juddering with FKMS that would also work and I could forget about KMS. Maybe my dpi timing is screwed up?

[7ank0v1c]

@phos
Did you get anywhere with this in the end?