BeagleBone Black Tips && Tricks

Beaglebone X uses framebuffer device, So adding a modeline in xorg.conf won't work. Likewise any fb-resolutions given on the kernelCL depend on that framebuffer-resolution already defined. In the end, none of that is really needed.

Steps:

1. generate a new fb config, using gtf <width> <height> <refreshrate> -f
2. add it to /etc/fb.modes
3. you're done, the rest happens automatically

fb.modes

mode "1440x900-60"
    # PCLK: 106.47 MHz, H: 55.92 kHz, V: 60.00 Hz
    geometry 1440 900 1440 900 32
    timings 9392 232 80 28 1 152 3
    hsync low
    vsync high
endmode

This can and should be done use X. Downside is you can't rotate the console like on the RPi. Accomplish it using the Rotate X-Option of the Framebuffer Device.

xorg.conf

Section "Device"
        Identifier      "Builtin Default fbdev Device 0"
        Driver          "fbdev"
        Option  "Rotate" "CCW"
EndSection
 
Section "Screen"
        Identifier      "Builtin Default fbdev Screen 0"
        Device          "Builtin Default fbdev Device 0"
        DefaultDepth    16
EndSection
 
Section "ServerLayout"
        Identifier      "Builtin Default Layout"
        Screen          "Builtin Default fbdev Screen 0"
EndSection

Basically, until the Device-Tree-Overlays are loaded, the Beageblone-Blacks gpio pins are in INPUT mode and sometimes, during bootup, may switch devices your relays and other stuff that depends on your pins being configured for OUTPUT at level 0, when powering up.

There are two possible solution that I know of.

1. Don't power up your external gpio-controlled hardware before the BeagleBoneBlack has booted
2. Guard your GPIO Pins with some Peripheral-Buffer IC's that need an ENable signal.

In both cases, you still need a pin to connect the EN signal or power-relay for our peripherals, a PIN that you can trust to pull your pheripheral LOW even during bootup.

A good choice for that are most pins that, per default, are muxed not to the GPIOchips but to internal devices like UART, SPI, I2C.

The following is a list of measurement, which pins pull which direction (HIGH/LOW) during bootup.

DTO-Generator