xref: /openbmc/u-boot/api/README (revision f4abbee3)
1U-Boot machine/arch independent API for external apps
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41.  Main assumptions
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6  - there is a single entry point (syscall) to the API
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8  - per current design the syscall is a C-callable function in the U-Boot
9    text, which might evolve into a real syscall using machine exception trap
10    once this initial version proves functional
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12  - the consumer app is responsible for producing appropriate context (call
13    number and arguments)
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15  - upon entry, the syscall dispatches the call to other (existing) U-Boot
16    functional areas like networking or storage operations
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18  - consumer application will recognize the API is available by searching
19    a specified (assumed by convention) range of address space for the
20    signature
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22  - the U-Boot integral part of the API is meant to be thin and non-intrusive,
23    leaving as much processing as possible on the consumer application side,
24    for example it doesn't keep states, but relies on hints from the app and
25    so on
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27  - optional (CONFIG_API)
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302. Calls
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32  - console related (getc, putc, tstc etc.)
33  - system (reset, platform info)
34  - time (delay, current)
35  - env vars (enumerate all, get, set)
36  - devices (enumerate all, open, close, read, write); currently two classes
37    of devices are recognized and supported: network and storage (ide, scsi,
38    usb etc.)
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413. Structure overview
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43  - core API, integral part of U-Boot, mandatory
44    - implements the single entry point (mimics UNIX syscall)
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46  - glue
47    - entry point at the consumer side, allows to make syscall, mandatory
48      part
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50    - helper conveniency wrappers so that consumer app does not have to use
51      the syscall directly, but in a more friendly manner (a la libc calls),
52      optional part
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54  - consumer application
55    - calls directly, or leverages the provided glue mid-layer
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