README 1.8 KB

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  1. U-Boot machine/arch independent API for external apps
  2. =====================================================
  3. 1. Main assumptions
  4. - there is a single entry point (syscall) to the API
  5. - per current design the syscall is a C-callable function in the U-Boot
  6. text, which might evolve into a real syscall using machine exception trap
  7. once this initial version proves functional
  8. - the consumer app is responsible for producing appropriate context (call
  9. number and arguments)
  10. - upon entry, the syscall dispatches the call to other (existing) U-Boot
  11. functional areas like networking or storage operations
  12. - consumer application will recognize the API is available by searching
  13. a specified (assumed by convention) range of address space for the
  14. signature
  15. - the U-Boot integral part of the API is meant to be thin and non-intrusive,
  16. leaving as much processing as possible on the consumer application side,
  17. for example it doesn't keep states, but relies on hints from the app and
  18. so on
  19. - optional (CONFIG_API)
  20. 2. Calls
  21. - console related (getc, putc, tstc etc.)
  22. - system (reset, platform info)
  23. - time (delay, current)
  24. - env vars (enumerate all, get, set)
  25. - devices (enumerate all, open, close, read, write); currently two classes
  26. of devices are recognized and supported: network and storage (ide, scsi,
  27. usb etc.)
  28. 3. Structure overview
  29. - core API, integral part of U-Boot, mandatory
  30. - implements the single entry point (mimics UNIX syscall)
  31. - glue
  32. - entry point at the consumer side, allows to make syscall, mandatory
  33. part
  34. - helper conveniency wrappers so that consumer app does not have to use
  35. the syscall directly, but in a more friendly manner (a la libc calls),
  36. optional part
  37. - consumer application
  38. - calls directly, or leverages the provided glue mid-layer