0bac2efd0e
Currently RISC-V NuttX supports 32-bit MMU Flags inside a Page Table Entry. This PR extends the MMU Flags to 64-bit, to support T-Head C906 Core and the new RISC-V Svpbmt Extension. T-Head C906 uses Bits 59 to 63 in a Leaf Page Table Entry to configure the Memory Type: Cacheable / Bufferable / Strongly-Ordered. For the upcoming port of NuttX to PINE64 Ox64 BL808 SBC, we need to set the Memory Type to Strongly-Ordered for I/O Memory, which requires 64-bit MMU Flags. Details of C906 MMU: https://lupyuen.github.io/articles/plic3#t-head-errata Newer RISC-V Cores will use the Svpbmt Extension to configure the Memory Type (Cacheable / Strongly-Ordered). Svpbmt uses Bits 61 to 62 in a Leaf Page Table Entry to define the Memory Type. This also requires 64-bit MMU Flags. Details of Svpbmt: https://github.com/riscv/riscv-isa-manual/blob/main/src/supervisor.adoc#svpbmt
Apache NuttX is a real-time operating system (RTOS) with an emphasis on standards compliance and small footprint. Scalable from 8-bit to 64-bit microcontroller environments, the primary governing standards in NuttX are POSIX and ANSI standards. Additional standard APIs from Unix and other common RTOSs (such as VxWorks) are adopted for functionality not available under these standards, or for functionality that is not appropriate for deeply-embedded environments (such as fork()).
For brevity, many parts of the documentation will refer to Apache NuttX as simply NuttX.
Getting Started
First time on NuttX? Read the Getting Started guide! If you don't have a board available, NuttX has its own simulator that you can run on terminal.
Documentation
You can find the current NuttX documentation on the Documentation Page.
Alternatively, you can build the documentation yourself by following the Documentation Build Instructions.
The old NuttX documentation is still available in the Apache wiki.
Supported Boards
NuttX supports a wide variety of platforms. See the full list on the Supported Platforms page.
Contributing
If you wish to contribute to the NuttX project, read the Contributing guidelines for information on Git usage, coding standard, workflow and the NuttX principles.
License
The code in this repository is under either the Apache 2 license, or a license compatible with the Apache 2 license. See the License Page for more information.