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I'm trying to use fbcp to mirror /dev/fb0 (the built in framebuffer) to /dev/fb1 however i just cannot get a picture with the native resolution of /dev/fb1 (320x240). I tried different settings in /boot/config.txt (i'm only stating the difference from default):

boot/config.txt:

framebuffer_width=320, framebuffer_height=240
disable_overscan=1

/var/log/messages:

Kernel command line: ... bcm2708_fb.fbwidth=320 bcm2708_fb.fbheight=240
fbcp[2113]: Primary display is 720 x 480

and a second try:

/boot/config.txt

disable_overscan=1
hdmi_ignore_edid=0xa5000080 
hdmi_group=1
hdmi_mode=13  # 240p

/var/log/messages:

Kernel command line: ... bcm2708_fb.fbwidth=720 bcm2708_fb.fbheight=240
fbcp[2116]: Primary display is 720 x 240

All this seems very inconsistent to me.

Edit: this might actually be a firmware bug. I have submitted a bug-report here: https://github.com/raspberrypi/firmware/issues/409

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framebuffer_width/height only set's the resolution of the text console.

hdmi_mode 13 is 720x240, what you are seeing is correct, I had the same initial dramas however found some information on how to set 320x240 using a custom mode:

Add the below to your config.txt file:

# uncomment if hdmi display is not detected and composite is being output
hdmi_force_hotplug=1

# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=2
hdmi_mode=87
hdmi_cvt=320 240 60 1 0 0 0

https://github.com/watterott/RPi-Display/blob/master/docu/FAQ.md

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