I've noticed that I don't get any HDMI output to a monitor if I connect the HDMI cable to the Pi after I plug in the power supply, because I have two RPis for one monitor -- one running Raspbmc, the other running RetroPie. Does anyone else have this problem / is this normal? If it is normal, why? And if not, what am I doing wrong with my setup?
/boot/config.txt and apply this settings:
hdmi_force_hotplug=1to force hot plugin of your screen,
config_hdmi_boostto boost the signal. Lower values are meant to be for short HDMI cables, larger for longer ones. But this can also apply for (older) HDMI displays, whose HDMI receivers are not sensitive enough, irrespective of cable length.
You can find more info here: elinux.org.
you're doing everything right, CEC negotiations happen once during the boot process, and this is the only time your TV could be properly detected. this is perfectly normal and most Pi's work the same way.
you may get some success trying to detect your TV later using "cec-client", however I did not try this myself and could not confirm nor deny the possibility.