RPI3B+ disable HDMI

[bob prohaska]

On Sat, Oct 31, 2020 at 09:59:38PM +0200, Stefan Parvu wrote:
> Hi,
> 
> We have started now testing our product using FreeBSD 12.2 on RPI3 and 3B+. 
> 
> I have a question how one can start to disable things from the board which are not needed, to save as much as possible power. For example starting with HDMI port. I am trying to do some basic tests running our data recorders with FreeBSD 12.2 only on batteries. (4 x 18650 Li-ion 3500 mAh). Would it boot from batteries. Has anyone tried before this?

At one time ISTR that no monitor in the HDMI port on powerup turned off
the port, at least to the extent that if a monitor was subsequently plugged
in it got no signal. Not sure if this is still true, nor whether it actually
reduced power consumption. 

hth,

bob prohaska