Apache NuttX is a mature, real-time embedded operating system (RTOS) https://nuttx.apache.org/
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Marco Casaroli e8f2c2eba3 arch/x86_64: make ARCH_INTEL64_HPET_ALARM buildable.
ARCH_INTEL64_HPET_ALARM is one of the three members of the "System Timer
Source" choice, but selecting it does not build.  Taking qemu-intel64:nsh on
master and moving the choice off ARCH_INTEL64_TSC_DEADLINE onto it:

  intel64/intel64_hpet_alarm.c:41:24: error:
      'CONFIG_ARCH_INTEL64_HPET_ALARM_CHAN' undeclared

ARCH_INTEL64_HPET_ALARM_CHAN lives inside "if INTEL64_HPET" and nothing
selects INTEL64_HPET.  Enabling that by hand moves the failure to link time,
because intel64_oneshot_lower.c is built only when INTEL64_ONESHOT is set:

  undefined reference to `oneshot_initialize'

Enabling INTEL64_ONESHOT as well finally reaches the real problem.
intel64_oneshot_lower.c implements the counter flavour of struct
oneshot_operations_s, which exists only with ONESHOT_COUNT:

  intel64_oneshot_lower.c: error: 'const struct oneshot_operations_s' has no
      member named 'start_absolute'
  intel64_oneshot_lower.c: error: implicit declaration of function
      'oneshot_count_init'
  intel64_oneshot_lower.c: error: initialization of
      'int (*)(struct oneshot_lowerhalf_s *, const struct timespec *)' from
      incompatible pointer type ... (four more of these)

ONESHOT, ONESHOT_COUNT and ONESHOT_FAST_DIVISION were selected by
ARCH_INTEL64_TSC_DEADLINE and by nothing else, so the other members of the
same choice could never be built.

Select the four from ARCH_INTEL64_HPET_ALARM as well.  INTEL64_ONESHOT
selects INTEL64_HPET in turn, which is what brings
ARCH_INTEL64_HPET_ALARM_CHAN into existence, so one added select closes all
three stages.

Impact: build only, and only for a configuration that could not be built
before.  No existing defconfig selects ARCH_INTEL64_HPET_ALARM.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
2026-08-04 01:43:41 +08:00
.github !arch/stm32: move stm32l1 and finalize the directory split 2026-07-03 10:27:27 +08:00
arch arch/x86_64: make ARCH_INTEL64_HPET_ALARM buildable. 2026-08-04 01:43:41 +08:00
audio tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
binfmt tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
boards tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
cmake cmake: Sanitize NAME for _main symbol generation 2026-08-03 20:59:22 +08:00
crypto tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
Documentation docs/raspberrypi-4b: Documentation about the SD card updated 2026-08-03 20:57:47 +08:00
drivers drivers/ioexpander/iso1i813t.c: fix error startup condition 2026-08-04 00:36:38 +08:00
dummy build: add initial cmake build system 2023-07-08 13:50:48 +08:00
fs tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
graphics tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
include lib/math32: Avoid __uint128_t casts for LDC ImportC 2026-08-03 22:20:43 +08:00
libs tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
mm tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
net tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
openamp tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
pass1 tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
sched tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
syscall tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
tools tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
video tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
wireless tools: fix stale archive members surviving a Kconfig-driven CSRCS change 2026-08-04 00:36:32 +08:00
.asf.yaml github: master branch protection tune. 2025-05-07 18:37:13 -05:00
.codespell-ignore-lines !boards: Remove NSH_ARCHINIT and board_app_initialize 2026-05-02 18:36:46 +08:00
.codespellrc arch/sim: replace macOS C++ constructor runtime hack with post-link patch 2026-05-19 07:08:55 -03:00
.editorconfig .editorconfig: fix character encoding property specification 2025-11-28 19:12:13 +08:00
.gitignore git: Specify multiple build directories in .gitignore. 2026-05-20 03:06:58 +08:00
.gitmessage docs/contributing: Add a commit message template 2025-06-03 17:33:24 +08:00
.pre-commit-config.yaml pre-commit: enable codespell checks 2025-05-05 12:34:39 +08:00
.yamllint feat: add a GitHub action to lint the YAML files 2020-12-15 09:52:04 -06:00
AUTHORS AUTHORS: add Eren Terzioglu 2026-05-20 15:17:00 +08:00
CMakeLists.txt cmake: Do not link an executable to detect the compiler. 2026-08-03 22:21:10 +08:00
CONTRIBUTING.md docs: Fix typos, formatting, and numbering in README.md and CONTRIBUTING.md. 2026-03-23 12:05:24 +01:00
INVIOLABLES.md
Kconfig sched/misc/assert: Add CONFIG_SCHED_DUMP_TASKS and CONFIG_SCHED_DUMP_STACK 2026-07-04 13:29:32 -04:00
LICENSE !arch/stm32: move stm32l1 and finalize the directory split 2026-07-03 10:27:27 +08:00
Makefile !boards: enforce secure ROMFS passwd and TEA key setup 2026-07-06 12:04:07 -03:00
NOTICE Remove the double blank line from source files 2022-02-20 20:10:14 +01:00
README.md docs: Fix typos, formatting, and numbering in README.md and CONTRIBUTING.md. 2026-03-23 12:05:24 +01:00
ReleaseNotes Documentation: move ReleaseNotes 2023-09-26 20:41:00 +08:00

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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.