I just wanted to share my experiences using the vga666 adapter to output native 240p video to an analog TV. I am using an older sony profeel with 34 pin microcomputer (RGB) input. The combination seems to work fine if you can manage to align the TV sync and pixel clock issues. The RPi has a strange limit to its lower frequency pixel clock values in that it has to be a value of 19.2 Mhz ÷ n, where 'n' is an integer value. This gives an option for 240-ish lines, but I still haven't got a good one working for 480i resolution.
Hers's my config.txt lines:
dtoverlay=vga666
enable_dpi_lcd=1
display_default_lcd=1
dpi_group=2 #2 for custom DMT
dpi_mode=87 #87 is custom timing below
hdmi_timings= 320 1 16 8 72 240 1 8 5 9 0 0 0 60 0 6400000 1 #320x240 CGA monitor for progressive scan
And here's an example of image produced, I hope it helps someone who was looking for a solution that does not involve a scan converter or interlaced video.
