Force HDMI Resolution to get a working dipslay

The newer image releases seem to be improving the operation of HDMI
"out of the box", but it still looks like many people are having
problems. If you don't see HDMI output or are having problems (like
the display disappears once the 'Bone has booted), you can try forcing
your resolution to something your monitor supports.

*ALL* HDMI monitors are *REQUIRED* to support 640x480@60 and one of
720x480@60 (NTSC) or 720x576@50 (PAL) depending on their native format.

To force the resolution, you need to add a kernel command line
parameter in the uBoot file on the FAT partition of the SD Card (or in
the eMMC boot partition if you're running out of the on-board memory).

The kernel command line parameter you need to pass is one of:

  video=HDMI-A-1:640x480@60
  video=HDMI-A-1:720x480@60
  video=HDMI-A-1:720x576@50

...and typically you would add this to the optargs= setting to get it
passed to the kernel, ie:

  optargs=video=HDMI-A-1:640x480@60

If your HDMI is still not working, you can verify you got the setting
actually passed to the kernel by looking at the kernel command line in
/proc. Here's mine (from a Debian based SD card boot):

$ cat /proc/cmdline
console=ttyO0,115200n8 video=HDMI-A-1:640x480@60 root=/dev/mmcblk0p2
ro rootfstype=ext4 rootwait fixrtc ip=

...if you see the "video=..." section and HDMI still isn't working,
something lower level is wrong.

Once you get HDMI working at all, you can start to play around and see
if you can get a higher resolution to work. The 'Bone can't handle
full 1080p, but 720p should work on almost any modern HDMI display:

NTSC (North America, Japan):
  video=HDMI-A-1:1280x720@60

PAL (Europe):
  video=HDMI-A-1:1280x720@50

...configuring your HDMI display to disable overscan so you can see
the entire image is left as an exercise for the reader! :slight_smile:

Note that my Samsung monitor/TV only disables overscan on one of the
two HDMI inputs, and you have to set the source name to "DVI-PC" or it
assumes you're feeding it from a video source and stretches the image
to get rid of any garbage at the edges.

- --
Charles Steinkuehler
charles@steinkuehler.net