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Modern hardware all supports a TSC_DEADLINE mode for the APIC timer, where the same GHz-scale 64 bit TSC used for performance monitoring becomes the free-running counter used for cpu-local timer interrupts. Being a free running counter that does not need to be reset, it will not lose time in an interrupt. Being 64 bit, it needs no rollover or clamping logic in the driver when presented with a 32 bit tick count. Being a proper comparator, it will correctly trigger interrupts for times set "in the past" and thus needs no minimum/clamping logic. The counter is synchronized across the system architecturally (modulo one burp where firmware likes to change the adjustment value) so usage is SMP-safe by default. Access to the 64 bit counter and comparator value are single-instruction atomics even on 32 bit systems, so it beats even the RISC-V machine timer in complexity (which was our reigning champ for "simplest timer driver"). Really this is just ideal for Zephyr. So rather than try to add support for it to the existing APIC driver and increase complexity, make this a new standalone driver instead. All modern hardware has what it needs. The sole gotcha is that it's not easily emulatable (qemu supports it only under kvm where they can freeload on the host TSC) so it can be exercised only on hardware platforms right now. Signed-off-by: Andy Ross <andrew.j.ross@intel.com> |
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west.yml | ||
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zephyr-env.sh |
.. raw:: html <a href="https://www.zephyrproject.org"> <p align="center"> <img src="doc/images/Zephyr-Project.png"> </p> </a> <a href="https://bestpractices.coreinfrastructure.org/projects/74"><img src="https://bestpractices.coreinfrastructure.org/projects/74/badge"></a> <a href="https://buildkite.com/zephyr/zephyr"> <img src="https://badge.buildkite.com/f5bd0dc88306cee17c9b38e78d11bb74a6291e3f40e7d13f31.svg?branch=master"></a> The Zephyr Project is a scalable real-time operating system (RTOS) supporting multiple hardware architectures, optimized for resource constrained devices, and built with security in mind. The Zephyr OS is based on a small-footprint kernel designed for use on resource-constrained systems: from simple embedded environmental sensors and LED wearables to sophisticated smart watches and IoT wireless gateways. The Zephyr kernel supports multiple architectures, including ARM Cortex-M, Intel x86, ARC, Nios II, Tensilica Xtensa, and RISC-V, and a large number of `supported boards`_. .. below included in doc/introduction/introduction.rst .. start_include_here Getting Started *************** Welcome to Zephyr! See the `Introduction to Zephyr`_ for a high-level overview, and the documentation's `Getting Started Guide`_ to start developing. Community Support ***************** Community support is provided via mailing lists and Slack; see the Resources below for details. .. _project-resources: Resources ********* Here's a quick summary of resources to help you find your way around: * **Help**: `Asking for Help Tips`_ * **Documentation**: http://docs.zephyrproject.org (`Getting Started Guide`_) * **Source Code**: https://github.com/zephyrproject-rtos/zephyr is the main repository; https://elixir.bootlin.com/zephyr/latest/source contains a searchable index * **Releases**: https://github.com/zephyrproject-rtos/zephyr/releases * **Samples and example code**: see `Sample and Demo Code Examples`_ * **Mailing Lists**: users@lists.zephyrproject.org and devel@lists.zephyrproject.org are the main user and developer mailing lists, respectively. You can join the developer's list and search its archives at `Zephyr Development mailing list`_. The other `Zephyr mailing list subgroups`_ have their own archives and sign-up pages. * **Nightly CI Build Status**: https://lists.zephyrproject.org/g/builds The builds@lists.zephyrproject.org mailing list archives the CI (buildkite) nightly build results. * **Chat**: Zephyr's Slack workspace is https://zephyrproject.slack.com. Use this `Slack Invite`_ to register. * **Contributing**: see the `Contribution Guide`_ * **Wiki**: `Zephyr GitHub wiki`_ * **Issues**: https://github.com/zephyrproject-rtos/zephyr/issues * **Security Issues**: Email vulnerabilities@zephyrproject.org to report security issues; also see our `Security`_ documentation. Security issues are tracked separately at https://zephyrprojectsec.atlassian.net. * **Zephyr Project Website**: https://zephyrproject.org .. _Slack Invite: https://tinyurl.com/y5glwylp .. _supported boards: http://docs.zephyrproject.org/latest/boards/index.html .. _Zephyr Documentation: http://docs.zephyrproject.org .. _Introduction to Zephyr: http://docs.zephyrproject.org/latest/introduction/index.html .. _Getting Started Guide: http://docs.zephyrproject.org/latest/getting_started/index.html .. _Contribution Guide: http://docs.zephyrproject.org/latest/contribute/index.html .. _Zephyr GitHub wiki: https://github.com/zephyrproject-rtos/zephyr/wiki .. _Zephyr Development mailing list: https://lists.zephyrproject.org/g/devel .. _Zephyr mailing list subgroups: https://lists.zephyrproject.org/g/main/subgroups .. _Sample and Demo Code Examples: http://docs.zephyrproject.org/latest/samples/index.html .. _Security: http://docs.zephyrproject.org/latest/security/index.html .. _Asking for Help Tips: https://docs.zephyrproject.org/latest/guides/getting-help.html