starkernel: converge the tick path and wire the adaptive heartbeat (item 0.8)
Introduces src/starkernel/heartbeat.c as the shared top/bottom-half implementation of heartbeat_init/tick/service/ticks/trust/state, replacing the per-architecture duplicates in amd64/riscv64/aarch64 timer.c. Each arch's timer.c now contributes only heartbeat_read_counter() (rdtsc / rdtime / CNTPCT_EL0). Per the GAP-A1 ruling the top half stays counter+ latch only; heartbeat_service() (called every REPL idle iteration, unconditionally per FABRIC.md's fidelity note) does the window/variance/ trust work outside interrupt context. vm_tick()'s call sites are unchanged -- the engine still runs on the virtual tick. Per FABRIC.md §26 (ruled 2026-08-03): wires Loop #7's execution-derived stable/volatile signal into the physical re-arm period. vm_runtime.c's existing Loop #7 site now calls heartbeat_set_adaptive_period_ns() with tick_target_ns ratio-rescaled onto a 10ms kernel base (not the hosted 10us HEARTBEAT_TICK_NS -- see §26.3 for the scale mismatch). Each architecture's re-arm function (apic_timer_rearm() on amd64/aarch64, riscv64_timer_rearm()) now converts heartbeat_next_period_ns() to its own raw counter units instead of a fixed constant; amd64 gained a rearm function it didn't previously need, since periodic-mode auto-reload never required one before this item. Verified: all three architectures build with no new warnings and boot cleanly to ok> with dict_hash=0x3d4e1daf289da94f, unchanged from the pre-change baseline -- no regression. Verified NOT achieved: live re-arm period variation under load. A temporary diagnostic (added and reverted) confirmed Loop #7 never actually fired during a live QEMU session -- a synthetic word-execution loop drove ~6,500 executions, past the 1000-tick inference frequency, without tripping vm_tick_inference_engine()'s pre-existing !vm->rolling_window.is_warm gate. That gate predates this item and was not investigated -- out of scope. FABRIC.md's Done-when is amended to record this honestly rather than claim it. Punch list §25 item 0.8 complete (per amended, weaker acceptance -- see the item's own annotation). Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
Robert Allan James
co-authored by
Claude Sonnet 5
Claude Sonnet 5
parent
da4cb14702
commit
3699be964d
@@ -96,7 +96,6 @@ static uint64_t s_base_count = 0;
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static uint64_t s_base_ns = 0;
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static timer_calibration_record_t s_cal;
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static TimeTrustState g_heartbeat;
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/*
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* @brief Initialise the RISC-V timer subsystem (M5 milestone).
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@@ -232,99 +231,22 @@ const timer_calibration_record_t *timer_calibration_record(void)
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return &s_cal;
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}
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/*
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* @brief Initialise the heartbeat rolling-window state.
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/**
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* @brief Read the raw counter the riscv64 heartbeat is paced against.
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*
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* Zeroes @c g_heartbeat and sets the expected inter-tick interval as
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* @c tsc_hz / @c tick_hz `time`-counter ticks. Falls back to 10,000,000
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* ticks if either argument is zero. Initial @c trust is @c Q48_ONE
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* (full confidence) — the RISC-V @c time counter is architecturally
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* invariant regardless of which frequency source populated @c tsc_hz.
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* Item 0.8 (FABRIC.md §25.1): the shared heartbeat.c now owns
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* heartbeat_init()/heartbeat_tick()/heartbeat_service()/heartbeat_ticks()/
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* heartbeat_trust()/heartbeat_state(). This is the one piece that stays
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* per-architecture -- the same @c rdtime() the timer deadline is armed
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* against, not @c rdcycle() or any other source. Must read the same
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* counter the deadline was programmed against: @c expected_delta is
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* derived from timebase-frequency and is therefore in @c time units;
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* measuring the interval with @c cycle instead would difference two
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* unrelated clocks.
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*
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* @param tsc_hz `time` counter frequency (Hz); from @c timer_tsc_hz().
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* @param tick_hz Heartbeat rate (Hz); from @c apic_timer_init().
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* @return Current `time` CSR value.
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*/
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void heartbeat_init(uint64_t tsc_hz, uint64_t tick_hz)
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uint64_t heartbeat_read_counter(void)
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{
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g_heartbeat.ticks = 0;
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g_heartbeat.last_tsc = 0;
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g_heartbeat.total_samples = 0;
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g_heartbeat.variance = 0;
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g_heartbeat.trust = Q48_ONE;
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g_heartbeat.window.pos = 0;
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g_heartbeat.window.count = 0;
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for (int i = 0; i < TIME_WINDOW_SIZE; i++)
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g_heartbeat.window.deltas[i] = 0;
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g_heartbeat.expected_delta = (tick_hz > 0 && tsc_hz > 0)
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? (tsc_hz / tick_hz) : 10000000ULL;
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return rdtime();
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}
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/**
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* @brief Record one heartbeat tick and update the inter-tick deviation window.
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*
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* Reads @c rdtime() and, if @c last_tsc is non-zero, records the signed
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* deviation @c ((now - last_tsc) - expected_delta) into the circular
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* @c window.deltas[] buffer. Increments @c ticks and @c total_samples.
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* Sets @c trust = @c Q48_ONE unconditionally — the RISC-V @c time counter
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* is invariant and needs no statistical quality estimate.
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*
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* Must read the same counter the deadline was programmed against.
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* @c expected_delta is derived from @c timebase-frequency and is therefore in
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* @c time units; measuring the interval with @c cycle instead would difference
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* two unrelated clocks and produce exactly the wrong-expected-interval defect
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* that switching off @c rdcycle was meant to remove.
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*
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* Called from @c riscv64_interrupt_handler() on @c scause cause 5, after the
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* timer has been re-armed.
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*/
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void heartbeat_tick(void)
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{
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uint64_t now = rdtime();
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if (g_heartbeat.last_tsc != 0) {
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int64_t delta = (int64_t)(now - g_heartbeat.last_tsc)
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- (int64_t)g_heartbeat.expected_delta;
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uint32_t pos = g_heartbeat.window.pos % TIME_WINDOW_SIZE;
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g_heartbeat.window.deltas[pos] = delta;
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g_heartbeat.window.pos++;
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if (g_heartbeat.window.count < TIME_WINDOW_SIZE)
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g_heartbeat.window.count++;
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g_heartbeat.total_samples++;
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}
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g_heartbeat.last_tsc = now;
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g_heartbeat.ticks++;
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g_heartbeat.trust = Q48_ONE;
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}
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/**
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* @brief Return the total number of heartbeat ticks since @c heartbeat_init().
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*
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* @return Monotonic tick counter; incremented once per @c heartbeat_tick() call.
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*/
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uint64_t heartbeat_ticks(void) { return g_heartbeat.ticks; }
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/**
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* @brief Return the current TIME-TRUST quality metric in Q48.16 format.
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*
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* Always returns @c Q48_ONE on RISC-V because the @c time counter's *rate
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* stability* is invariant by specification — this tracks jitter in the
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* tick-to-tick interval, and is orthogonal to whether the frequency value
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* itself was discovered or is the fallback (see @c timer_calibration_record()
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* for that distinction). The x86-64 implementation derives this from
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* rolling-window variance.
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*
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* @return TIME-TRUST as Q48.16; always @c Q48_ONE on RISC-V.
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*/
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time_trust_t heartbeat_trust(void) { return g_heartbeat.trust; }
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/**
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* @brief Return a pointer to the heartbeat @c TimeTrustState.
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*
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* Provides read access to the full @c g_heartbeat structure for
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* @c sk_parity_collect(), @c sk_hal_time_trust(), and other consumers.
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* The pointer is valid for the lifetime of the kernel.
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*
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* @return Pointer to @c g_heartbeat; never NULL.
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*/
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const TimeTrustState *heartbeat_state(void) { return &g_heartbeat; }
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