U-Boot machine/arch independent API for external apps
  =====================================================
  
  1.  Main assumptions
  
    - there is a single entry point (syscall) to the API
  
    - per current design the syscall is a C-callable function in the U-Boot
      text, which might evolve into a real syscall using machine exception trap
      once this initial version proves functional
  
    - the consumer app is responsible for producing appropriate context (call
      number and arguments)
  
    - upon entry, the syscall dispatches the call to other (existing) U-Boot
      functional areas like networking or storage operations
  
    - consumer application will recognize the API is available by searching
      a specified (assumed by convention) range of address space for the
      signature
  
    - the U-Boot integral part of the API is meant to be thin and non-intrusive,
      leaving as much processing as possible on the consumer application side,
      for example it doesn't keep states, but relies on hints from the app and

      so on

  
    - optional (CONFIG_API)
  
  
  2. Calls
  
    - console related (getc, putc, tstc etc.)
    - system (reset, platform info)
    - time (delay, current)
    - env vars (enumerate all, get, set)
    - devices (enumerate all, open, close, read, write); currently two classes
      of devices are recognized and supported: network and storage (ide, scsi,
      usb etc.)
  
  
  3. Structure overview
  
    - core API, integral part of U-Boot, mandatory
      - implements the single entry point (mimics UNIX syscall)
  
    - glue
      - entry point at the consumer side, allows to make syscall, mandatory
        part
  
      - helper conveniency wrappers so that consumer app does not have to use
        the syscall directly, but in a more friendly manner (a la libc calls),
        optional part
  
    - consumer application
      - calls directly, or leverages the provided glue mid-layer