Display frontend on VGA666 CRT instead of HDMI with Pi4 and KMS

TomBruise

Hello! I am using RetroPie 4.8.4 on a Pi4. Image was installed using RaspberryPi Imager.
I am using libretro from master (installed from source after instructing retropie-setup.sh to fetch from master).

I have a setup with a CRT screen connected to a VGA666 adapter, and a second screen connected via HDMI to be used as a dynamic marquee.

Using fkms/legacy I am able to display emulators/frontends (tried with attractmode and emulationstation) on the CRT screen while the HDMI is connected. To my understanding, this is accomplished with these lines in config.txt:

enable_dpi_lcd=1
display_default_lcd=1

I then switched to KMS, mainly because I am interested in using the KMS-based SwitchRes integration recently added in Retroarch. After generating an EDID for the CRT screen using SwitchRes, I am able to display emulators on the CRT screen when the HDMI marquee is unplugged.

When I boot with the marquee plugged in (either HDMI 0 or 1) , the HDMI screen becomes the "main" display, emulators are shown there instead of the CRT, and I can only see console output on the CRT.

What is the correct way to display frontends and emulators on the CRT with KMS and this configuration?

I am attaching my config and cmdline files below.

Thanks!

config.txt:

# For more options and information see
# http://rpf.io/configtxt
# Some settings may impact device functionality. See link above for details

# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1

# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
#disable_overscan=1

# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
#overscan_left=16
#overscan_right=16
#overscan_top=16
#overscan_bottom=16

# uncomment to force a console size. By default it will be display's size minus
# overscan.
#framebuffer_width=1280
#framebuffer_height=720

# uncomment if hdmi display is not detected and composite is being output
#hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1

# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
#hdmi_drive=2

# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
#config_hdmi_boost=4

# uncomment for composite PAL
#sdtv_mode=2

#uncomment to overclock the arm. 700 MHz is the default.
#arm_freq=800

# Uncomment some or all of these to enable the optional hardware interfaces
#dtparam=i2c_arm=on
#dtparam=i2s=on
#dtparam=spi=on

# Uncomment this to enable infrared communication.
#dtoverlay=gpio-ir,gpio_pin=17
#dtoverlay=gpio-ir-tx,gpio_pin=18

# Additional overlays and parameters are documented /boot/overlays/README

# Enable audio (loads snd_bcm2835)
dtparam=audio=on 
dtparam=i2c_arm=off
dtparam=i2s=off
dtparam=spi=off
enable_uart=0
boot_delay=5

[pi4]
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
#dtoverlay=vc4-fkms-v3d
#dtoverlay=vga666

dtoverlay=vc4-kms-v3d-pi4,nohdmi0
dtoverlay=vc4-kms-vga666,ddc


gpio=2-21=a2
disable_overscan=1
max_framebuffers=2
enable_dpi_lcd=1
display_default_lcd=1
dpi_group=2
dpi_mode=87
hdmi_drive=1
hdmi_timings 320 1 15 30 42 240 1 4 3 15 1 0 0 60 0 6400000 1

cmdline.txt:

console=serial0,115200 console=tty1 root=PARTUUID=e643d180-02 rootfstype=ext4 fsck.repair=yes rootwait loglevel=3 consoleblank=0 plymouth.enable=0 video=VGA-1:320x240M@60e drm.edid_firmware=VGA-1:arcade_15.bin video=HDMI-A-1:800x600@60e

mitu

[...]
What is the correct way to display frontends and emulators on the CRT with KMS and this configuration?
[...]

I'm surprised this configuration worked with fkms, but I think it's no longer going to work on kms alone. I've seen your - similar - post on the RPI forums, the definitive answer if this configuration is supported should come from a RP engineer (6by9 is their expert on this).

EDIT: one thing to note, the RetroPie image is currently based on the legacy RaspiOS buster version, a lot of work has been done on the pure KMS driver on the current Linux kernel. You can get the current RP Linux kernel with rpi-update (not recommended) or by manually installing RetroPie on current RaspiOS bullseye (still in beta at the moment), my recommendation would be the latter.

I guess you're using the RetroArch master for the switchres support added after v1.15 ?

TomBruise

@mitu said in Display frontend on VGA666 CRT instead of HDMI with Pi4 and KMS:

Thanks for taking the time to answer!

I'm surprised this configuration worked with fkms, but I think it's no longer going to work on kms alone. I've seen your - similar - post on the RPI forums, the definitive answer if this configuration is supported should come from a RP engineer (6by9 is their expert on this).

Yeah, that's the first place I asked. I was hoping it was some stupid mistake on my side.

EDIT: one thing to note, the RetroPie image is currently based on the legacy RaspiOS buster version, a lot of work has been done on the pure KMS driver on the current Linux kernel. You can get the current RP Linux kernel with rpi-update (not recommended) or by manually installing RetroPie on current RaspiOS bullseye (still in beta at the moment), my recommendation would be the latter.

I did try a rpi-update as an extreme attempt, ready to start from scratch. Unfortunately the situation didn't change.

The other idea is to have a second Pi driving the marquee, which is a solution I have mostly working with one last annoying quirk that I wasn't able to iron out yet.
It would be great to do everything from one device though.

I guess you're using the RetroArch master for the switchres support added after v1.15 ?

Yes that's correct. And it seems to work great, possibly much better than the "old" Pi3-style runcommand trickery based on fbset and vcgencmd.