RISC-V Open Source Supervisor Binary Interface (OpenSBI)
========================================================

The **RISC-V Supervisor Binary Interface (SBI)** is a recommended
interface between:

1. A platform specific firmware (M-mode) and a general purpose
   OS or hypervisor or bootloader (S-mode or HS-mode).
2. A hypervisor (HS-mode) and a general purpose OS or bootloader (VS-mode)

The *RISC-V SBI specification* is maintained as an independent project
by the RISC-V Foundation in [Github](https://github.com/riscv/riscv-sbi-doc)

OpenSBI aims to provides an open-source and extensible implementation of
the RISC-V SBI specification for case 1 mentioned above. OpenSBI
implementation can be easily extended by RISC-V platform or System-on-Chip
vendors to fit a particular hardware configuration.

OpenSBI provides three components:

1. *libsbi.a* - A generic OpenSBI static library
2. *libplatsbi.a* - Platform specific OpenSBI static library, that is,
                    libsbi.a plus platform specific hooks
3. *firmwares* - Platform specific bootable firmware binaries

Building and Installing generic *libsbi.a*
------------------------------------------

For cross-compiling, the environment variable *CROSS_COMPILE* must
be defined to specify the toolchain executable name prefix, e.g.
*riscv64-unknown-elf-* if the gcc executable used is
*riscv64-unknown-elf-gcc*.

To build the generic OpenSBI library *libsbi.a*, simply execute:
```
make
```

All compiled binaries will be placed in the *build* directory.
To specify an alternate build directory target, run:
```
make O=<build_directory>
```

To generate files to be installed for using *libsbi.a* in other projects,
run:
```
make install
```
This will create the *install* directory with all necessary include files
and binary files under it. To specify an alternate installation directory,
run:
```
make I=<install_directory> install
```

Building and Installing platform specific *libsbi.a* and firmwares
------------------------------------------------------------------

The libplatsbi.a and firmware files are only built if the
*`PLATFORM=<platform_subdir>`* argument is specified on make command lines.
*`<platform_subdir>`* must specify the path to one of the leaf directories
under the *`platform`* directory. For example, to compile the library and
firmware for QEMU RISC-V *virt* machine, *`<platform_subdir>`*
should be *`qemu/virt`*.

To build *libsbi, libplatsbi, and firmwares* for a specific platform, run:
```
make PLATFORM=<platform_subdir>
or
make PLATFORM=<platform_subdir> O=<build_directory>
```

To install *libsbi, headers, libplatsbi, and firmwares*, run:
```
make PLATFORM=<platform_subdir> install
or
make PLATFORM=<platform_subdir> I=<install_directory> install
```

In addition, platform specific make command-line options to top-level make
, such as *PLATFORM_<xyz>* or *FW_<abc>* can also be specified. These
options are described under *`docs/platform/<platform_name>.md`* and
*`docs/firmware/<firmware_name>.md`*.

License
-------------
The software is provided under a BSD-2-Clause license. Contributions to this
project are accepted under the same license with developer sign-off as
described in the [Contributing Guidelines](docs/contributing.md).

This project also contains code from other projects as listed below. The original
license text is included in those source files.

1. The libfdt source code is disjunctively dual licensed (GPL-2.0+ OR BSD-2-Clause). It is
   used by this project under the terms of the BSD-2-Clause license. Any contributions to
   this code must be made under the terms of both licenses.

Documentation
-------------

A more detailed documentation is under the *docs* directory and organized
as follows.

* *`docs/contributing.md`* - Guidelines for contributing to OpenSBI project
* *`docs/platform_guide.md`* - Guidelines for adding new platform support
* *`docs/library_usage.md`* - Guidelines for using the static library
* *`docs/platform/<platform_name>.md`* - Documentation for the platform *<platform_name>*
* *`docs/firmware/<firmware_name>.md`* - Documentation for the firmware *<firmware_name>*

The source code is also well documented. For source level documentation,
doxygen style is used. Please refer to [Doxygen manual] for details on this
format.

[Doxygen manual]: http://www.stack.nl/~dimitri/doxygen/manual.html

The Doxygen can be installed on your debian build system using following:
```
sudo apt-get install doxygen doxygen-latex doxygen-doc doxygen-gui graphviz
```

To build a consolidated `refman.pdf` of all documentation, run:
```
make docs
or
make O=<build_directory> docs
```

**NOTE:** `refman.pdf` will be available under `<build_directory>/docs/latex`.

To install a consolidated `refman.pdf` of all documentation, run:
```
make install_docs
or
make I=<install_directory> install_docs
```

**NOTE:** `refman.pdf` will be installed under `<install_directory>/docs`.