[yocto] Making a derivative BSP layer - where did I go wrong?

[Adam Rossi]

Howdy folks. I am having trouble making a derivative BSP layer and am
asking for your help in determining what I am doing wrong.

I am developing a Yocto distro for a beaglebone-based prototype.  I
made a few small changes directly to the meta-yocto-bsp layer and
bitbaked the core-image-sato image, and everything worked great. The
tweaks I made included:

* Edited meta-yocto-bsp/conf/machine/beaglebone.conf to include
additional machine features:

     * MACHINE_FEATURES = "usbgadget usbhost vfat alsa touchscreen"

* Edited meta-yocto-bsp/recipes-kernel/linux/linux-yocto_3.14.bbappend
to include a cfg file with the following entries:

      * CONFIG_HID_MULTITOUCH=y
        CONFIG_INPUT_MOUSEDEV_SCREEN_Y=600
        CONFIG_INPUT_MOUSEDEV_SCREEN_X=1024

While this works perfectly, it does not feel like a clean solution to
be mucking with the meta-yocto-bsp layer directly. So I created my own
meta-custom BSP layer using the yocto-bsp script to hold these
changes. My bsp-layer has  the following attributes:

*  meta-custom/conf/machine/custom.conf contains the following:

       * require /home/me/poky/meta-yocto-bsp/conf/machine/beaglebone.conf

          MACHINEOVERRIDES = "beaglebone:custom"

          MACHINE_FEATURES = "usbgadget usbhost vfat alsa touchscreen"

*  meta-custom/recipes-kernel/linux/linux-yocto_3.14.bbappend contains
a single line    SRC_URI += to the cfg file mentioned above

When I bitbake the new layer with the new custom machine and the same
image target, I get file outputs which look very similar to the edited
meta-yocto-bsp, with the exception of the zImage, which is much
smaller and will not boot.

Perhaps I have an improper understanding of how layers build upon each
other? I had though that by including meta-yocto-bsp and meta-custom,
and specifying my custom machine in the local.conf file, it would
build the exact same image as my tweaked meta-yocto-bsp.

Your guidance as to my mistake or a pointer to an example of a
derivative bsp-layer would be most appreciated.