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The NXP PCF8563 is a battery backed I2C clock at the fixed address 0x51, common on RISC-V and ARM boards, and NuttX had no driver for it. The nearest part in the tree, the PCF85263, has a different register map. The driver follows the shape of the external I2C clocks already here, ds3231 and pcf85263: board logic calls pcf8563_rtc_initialize() once the bus exists, and the chip then answers up_rtc_getdatetime() and up_rtc_settime() for the system clock. Three behaviours are deliberate. The top bit of the seconds register means the oscillator has stopped since the time was last set, so every register after it holds whatever it stopped on. A read in that state returns -ENODATA rather than the contents: a caller told the time is unknown can act on that, one told a wrong time cannot. A flat backup cell and a clock that has never been set both arrive here. The top bit of the month register marks a century rollover, but which value means which century is a convention that parts disagree on, so no century is read from it. The chip is treated as a clock for 2000 to 2099, the bit is written back as it was read, and a date outside those years is refused rather than stored as one that would read back different. This is what the mainline Linux driver does. The counters are stopped across a write so a carry cannot land between the seconds and the minutes, and restarted even when the write failed, since the alternative is leaving the clock stopped. The alarm and countdown timer are not implemented; their registers are defined. Assisted-by: Claude:claude-opus-5 Signed-off-by: Justin Hammond <justin@dynam.ac> |
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| arch | ||
| audio | ||
| binfmt | ||
| boards | ||
| cmake | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| dummy | ||
| fs | ||
| graphics | ||
| include | ||
| libs | ||
| mm | ||
| net | ||
| openamp | ||
| pass1 | ||
| sched | ||
| syscall | ||
| tools | ||
| video | ||
| wireless | ||
| .asf.yaml | ||
| .codespell-ignore-lines | ||
| .codespellrc | ||
| .editorconfig | ||
| .gitignore | ||
| .gitmessage | ||
| .pre-commit-config.yaml | ||
| .yamllint | ||
| AUTHORS | ||
| CMakeLists.txt | ||
| CONTRIBUTING.md | ||
| INVIOLABLES.md | ||
| Kconfig | ||
| LICENSE | ||
| Makefile | ||
| NOTICE | ||
| README.md | ||
| ReleaseNotes | ||
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.