micheleandClaude Sonnet 5
0e73eb4726
Was a separate, untracked directory (DataSheet/) outside the repo. Renamed to lowercase and moved in as hardware/v2/docs/datasheet/, with its own .gitignore for LaTeX build byproducts (compiled PDFs stay tracked, .aux/.log/.toc/etc do not). Now versioned and shares this repo's own remote instead of living untracked on disk. Content: IT+EN LaTeX chapter sources, reference manufacturer PDFs, and compiled datasheet PDFs including the 2026-09-07 SDRAM upgrade addendum (AS4C32M16SB-7BIN part/pinout/timing) in the v2-en chapters. Note: hardware/v2/docs/DatasheetLatex/ (and the v1 sibling) is a separate, already-tracked, differently-structured LaTeX document that predates this move -- left untouched, not merged, since its chapter set and content differ and merging was not requested. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_013xXuuRUWZScuo1DeYJxs3v
67 lines
3.7 KiB
TeX
67 lines
3.7 KiB
TeX
\chapter{Dataflow scheduling}
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\label{ch:sched}
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\section{Node lifecycle}
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\begin{center}
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\begin{tikzpicture}[font=\scriptsize,node distance=16mm,>=Stealth]
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\node[fnstate](e){EMPTY};
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\node[fnstate,right=of e](w){WAITING};
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\node[fnstate,right=of w](r){READY};
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\node[fnstate,right=of r](d){DISPATCHED};
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\draw[fnarrow] (e) -- node[fnlbl,above]{register, deps$>$0} (w);
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\draw[fnarrow] (e) to[bend left=25] node[fnlbl,above]{register, deps$=$0} (r);
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\draw[fnarrow] (w) -- node[fnlbl,above]{all producers done} (r);
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\draw[fnarrow] (r) -- node[fnlbl,above]{Director accepts} (d);
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\end{tikzpicture}
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\end{center}
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\code{DISPATCHED} is terminal (\S\ref{ch:arch}): a real, honest
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consequence, not an oversight --- see the roadmap (ch.~\ref{ch:roadmap})
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for the deferred slot-reclamation work item.
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\section{Verified graph topologies}
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\begin{tabularx}{\textwidth}{L{3.4cm} Y}
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\toprule
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\rowh \thd{Topology} & \thd{What it proves} \\
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\midrule
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Shared producer, 2 consumers & One node's completion resolves the dependency count of \emph{two} different waiting nodes independently. \\
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\rowa Multiple producers, 1 consumer & A node with \code{required}$>$1 only becomes \code{READY} once \emph{every} listed producer has completed, tracked across separate wake-up events. \\
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2-hop transitive diamond ($A,B$ independent; $C$ dep-$A$; $D$ dep-$B$; $E$ dep-$C,D$) & Correct cascading wake-up two hops deep --- $E$ does not fire until $C$ and $D$ have \emph{themselves} genuinely completed, not merely been marked ready. \\
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\rowa Mixed-depth fan-in (node depending on both a root and a 1-hop descendant) & Dependency resolution does not assume a uniform graph depth. \\
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Multilayer (8 layer-1 neurons, random INT8 data, feeding 2 layer-2 neurons reading their real shared result bytes) & Real cross-node \emph{data} forwarding through real PSRAM --- layer-2's golden values are computed from the real bytes layer-1 actually wrote, not from an independent expectation. \\
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\bottomrule
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\end{tabularx}
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All topologies above were exercised with the real, full
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\code{neural\_multiprocessor.v} (real V1 PSRAM chain, real
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\code{slot\_mem\_arbiter.v}) and verified bit-exact against a software
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golden model.
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\section{First-free dispatch}
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The Neural Director's own scheduling policy is deliberately the simplest
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one that is provably correct: a fixed, lowest-index priority scan over
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currently-free slots. Round-robin, least-loaded, or any fairness-aware
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alternative was explicitly deferred until real measured data showed
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whether it mattered (\S\ref{sec:fairness}).
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\section{Measured scheduling behavior}
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\label{sec:fairness}
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Real per-slot data (\code{N\_SLOTS}=4, a 128-neuron dense-layer
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workload) shows a striking imbalance: slots~0 and~1 each deliver 1008
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real tiles, while slots~2 and~3 deliver only 16 each --- despite all four
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slots reporting near-100\% ``busy'' utilization. The cause is not
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unfairness in isolation: once the shared PSRAM port is saturated
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(ch.~\ref{ch:mem}), there is rarely a moment where the low-index slots
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are simultaneously busy \emph{and} the high-index slots have nothing to
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do, so the fixed low-index-first scan keeps re-selecting the same two
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slots. This is a real, measured limitation of the current scheduler,
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carried into ch.~\ref{ch:roadmap} as an open item rather than patched
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without first measuring whether it is worth the added complexity for
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real workloads.
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\section{Correctness guarantees (measured, not assumed)}
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Across the full final benchmark campaign (6 workloads $\times$ 4
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\code{N\_SLOTS} configurations, re-verified after both memory
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optimizations): \textbf{zero} lost jobs, \textbf{zero} duplicated jobs
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(\code{jobs\_allocated == jobs\_completed == neurons\_completed} exactly,
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every run), \textbf{zero} deadlocks, \textbf{zero} timeouts, correct
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multi-hop dependency wake-up in every topology tested.
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