I have a Pioneer rear projection TV that only allows HD in the form of a VGA connector and ONLY 1080i.
I am going out of the Pi in HDMI into an HDMI to VGA adapter box shown here on amazon.
I have in the
config.txt the following:
hdmi_group=1 hdmi_mode=5 arm_freq=850 core_freq=375 force_turbo=1 disable_overscan=1 gpu_mem=128 start_file=start_x.elf fixup_file=fixup_x.dat hdmi_force_hotplug=1 hdmi_drive=2 #hdmi_ignore_hotplug=1
When the pi starts to boot, I see the Logo in what seems to be in 1080i clearly and stable, then as it continues to boot everything goes nuts as if it is going into a resolution that is not supported by my tv.
I then tried to boot with the same config on my samsung plasma and it does indeed start in 1080i, then drops back to 640x480.