[AD] Supporting a new platform/device

[Mark Watkin <devhead@xxxxxxxxxxxx>]

Hello all,

  I put a thread up on allegro.cc, but it's locked, so I thought I'd
  reask here.

  I want to get an Allegro build running on the Odroid Go Advance.
  (https://www.hardkernel.com/shop/odroid-go-advance-black-edition-clear-white/)

  It's a Linux machine, but the reference image doesn't have X11; and
  the display uses KMS/DRM. I don't really understand all the
  different driver components in Linux, but OtherCrashOverride has a
  library for access the Go Advance hardware, and his "RetroRun2"
  shows usage of EGL and GLES2
  https://github.com/OtherCrashOverride/libgo2
  https://github.com/OtherCrashOverride/retrorun-go2/blob/master/src/video.cpp


  I created a "Toolchain-odroidgoadv.cmake" in the cmake directory,
  but, building on the OGA just uses the regular linux toolchain (the
  compilation only fails due to missing GL header files).

  So is creating a new Toolchain file the right way to add support to
  the device?

  I also then created a folder /src/odroidgoadv, and dropped in there
  a file called ogajoy.c, which contains my inital joystick code
  (based on the /src/sdl/sdl_joystick.c file), and I'll create
  "ogadisplay.c" for the display and "ogasystem.c" for configuring the
  system VTable, and just copy the majority from the linux base, but redirect
  joystick and graphics to my new functions.

  Again, is this the right way of doing it? And if so, what causes the
  selection of the ALLEGRO_SYSTEM_INTERFACE?

  Does this all sound like the correct approach?

  Regards,
    Mark