Here is another way to boot into a single rom on a pi. This is using retropie 4.02
Use win32diskimager to install retropie on your sd card.
Setup retropie as per normal configuring controllers and adding roms etc.
Exit emulationstation to the retropie prompt.
type sudo nano /boot/cmdline.txt
when this opens you should see one line of commands, it must stay as one line.
look for console=tty1 replace it with console=tty3
at the end of the line add, quiet loglevel=3 then add logo.nologo
control x to bring up exit hit Y then enter to overwrite
type sudo nano /boot/config.txt
scroll to bottom of file add the following lines
this will stop the raspberry temperture icon showing during boot.
You need to enable splashscreens.
The Splash Screen Menu can be accessed from the RetroPie Menu in EmulationStation or through the setup script under option 3.
Choose Own Splashscreen: Once you've opened up the splashscreen menu in the setup script at least once a folder will be created in /home/pi/RetroPie/splashscreens you can also access this splashscreens folder from samba shares once its created. (Note you may need to install or restart samba shares from the setup script for the splashscreens folder to show up over samba shares) Make sure you create a new folder to place your splashscreen in
I created a folder called splashscreen black and placed the png file in there.
Open the splashscreen menu, choose splashscreen you then should see your custom splashscreen folder choose the file you added as your splashscreen.
reboot and hopefully you should see no boot messages
booting into a single rom
On RetroPie 4.0 there is /opt/retropie/configs/all/autostart.sh edit it
and add as the top line
/opt/retropie/supplementary/runcommand/runcommand.sh 0 _SYS_ mame-mame4all ~/RetroPie/roms/mame-mame4all/romname
/opt/retropie/supplementary/runcommand/runcommand.sh 0 _SYS_ mame-libretro ~/RetroPie/roms/mame-libretro/romname
Here is a quick vid of it booting up, no boot text, straight into the rom.https://www.youtube.com/watch?v=5cfR2VTzPI0