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Issue created by <a href="https://gitlab.rtems.org/wmthornton-dev">Wayne Thornton</a>: <a href="https://gitlab.rtems.org/rtems/docs/rtems-docs/-/work_items/149">#149</a>
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<h2 id="user-content-description" dir="auto" style="margin-top: 0px; margin-bottom: 10px;" align="initial">Description:<a href="#description" aria-label="Link to heading 'Description:'" data-heading-content="Description:" class="anchor" style="margin-top: 0px;"></a>
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<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">We have introduced a new Super Core architecture hook, <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">_CPU_Spin_wait()</code>, to mitigate aggressive speculative execution penalties, reduce thermal load, and lower bus contention during SMP spin-wait polling loops. The reference template is currently documented in <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">cpukit/score/cpu/no_cpu/include/rtems/score/cpu.h</code> and natively implemented for <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">x86_64</code> upon merging of <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1256" title="cpukit/score/.../cpu.h: Implement _CPU_Spin_wait()" class="gfm gfm-merge_request" data-original="rtems/rtos/rtems!1256" data-link="false" data-link-reference="false" data-merge-request="2627" data-project="26" data-project-path="rtems/rtos/rtems" data-iid="1256" data-container="body" data-placement="top" data-reference-type="merge_request">rtems/rtos/rtems!1256</a> and closing of <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5648" title="[x86_64] Implement _CPU_Spin_wait() in cpu.h for SMP spin-loop throttling" class="gfm gfm-issue" data-original="rtems/rtos/rtems#5648" data-link="false" data-link-reference="false" data-issue="29830" data-project="26" data-iid="5648" data-namespace-path="rtems/rtos/rtems" data-project-path="rtems/rtos/rtems" data-issue-type="issue" data-container="body" data-placement="top" data-reference-type="issue">rtems/rtos/rtems#5648</a></p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">The RTEMS CPU Architecture Supplement (<code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">rtems-docs/cpu-supplement</code>) needs to be updated to formalize this interface for future architecture and BSP maintainers.</p>
<h2 id="user-content-suggested-implementation" dir="auto" style="margin-top: 20px; margin-bottom: 10px;" align="initial">Suggested Implementation:<a href="#suggested-implementation" aria-label="Link to heading 'Suggested Implementation:'" data-heading-content="Suggested Implementation:" class="anchor" style="margin-top: 0px;"></a>
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<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">CPU Porting Guide Chapter: Add a new documentation entry under the CPU architecture support functions/macros section (alongside interfaces such as <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">_CPU_Context_switch</code> and <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">_CPU_Thread_Idle_body</code>). The documentation should detail:</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">The purpose of the hook: throttling the processor instruction pipeline during tight polling loops to prevent speculative execution floods and memory controller saturation.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">The default fallback behavior: utilizing <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">RTEMS_COMPILER_MEMORY_BARRIER()</code> when no native hardware instruction is available, guaranteeing compliance with the C memory model during busy-loops.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">The guidelines for architecture maintainers: overriding the default implementation with an optimal inline assembly pause/yield instruction (e.g., <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">pause</code> on x86_64/RISC-V or <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">yield</code> on ARM/AArch64).</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">x86_64 Architecture Chapter: Add a brief note under the target-specific or SMP features section documenting that <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">_CPU_Spin_wait()</code> is natively implemented for <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">x86_64</code> using the <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">pause</code> instruction.</p>
<p dir="auto" style="color: #3a383f; margin: 0px;" align="initial">Verification:
Validate that the Sphinx documentation builds cleanly without syntax or cross-referencing errors using <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">make html</code> (or the equivalent <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">Waf</code> doc build command) within the <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">rtems-docs</code> repository, and verify that the new section renders correctly in the generated HTML output.</p>
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