| 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 |