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.
config.txt. Or try using the command
tvservice -e "CEA 5"which should make the same settings. See elinux.org/RPiconfig for more info on hdmi_group and hdmi_mode.