How do I force the correct screen resolution in /boot/config.txt?

Question

I've recently set up a Retropie which I have plugged into my TV. If I have the right input selected on the TV before powering on the Pi, then the image looks crisp and wonderful. However if I turn on the Retropie first and then flip the input over, it seems as though it chooses a default resolution which is not ideal because it isn't able to auto-detect anything.

Currently I have these two lines uncommented in my /boot/config.txt file:

hdmi_force_hotplug=1
hdmi_drive=2

I believe I need to set some combination of hdmi_group and hdmi_mode in order to force it to automatically choose the proper resolution (or maybe overscan_ or framebuffer_ values?). But I found the documentation to be very terse and am unsure what the proper values would be.

For reference, here is the output I get when I call fbset -s when the input is correct:

mode "1824x984"
    geometry 1824 984 1824 984 32
    timings 0 0 0 0 0 0 0
    rgba 8/16,8/8,8/0,8/24
endmode

And here's what I get from that same command when the input is not correctly set before booting:

mode "640x480"
    geometry 640 480 640 480 32
    timings 0 0 0 0 0 0 0
    rgba 8/16,8/8,8/0,8/24
endmode

What do I need to change to ensure it always boots with a fixed resolution of 1824x984?

Answer 1

You simply uncomment the line and set it with the resolution of the TV :

framebuffer_width=1824 #set the resolution of the TV
framebuffer_height=984 #set the resolution of the TV    

in /boot/config.txt

Answer 2

Setting only framebuffer_width/framebuffer_height was not enough for me.

Had to resort to raspi-config which set these parameters in /boot/config.txt:

framebuffer_width=1920
framebuffer_height=1080
hdmi_force_hotplug=1
hdmi_group=2
hdmi_mode=82