# Gauge / display cadence — why the cockpit instruments update slowly (2026-08-04)

Operator report: "the rendering of the displays — many seconds between
updates" on BTL4REC vs "the original."  This file is the evidence chain.
All measurements on the dev rig, `pod_render_bgprobe.conf` (no per-frame
logs), DOSBox-X `cycles=max`, arena1 self-drive (BT_FORCE_THROTTLE=0.6).

## The mechanism (all verified in source AND the shipped binary)

1. **The manager runs flat-out by design.**  `main` passes
   `GetTicksPerSecond()` to `ApplicationManager(Scalar frame_rate)`, so
   `frameDuration = 1/ticksPerSecond` — a microscopic frame budget.
   Verified in the shipped exe: the ctor constant `_DAT_0044f2d8` at
   file offset 0x4f0d8 of BTL4OPT.EXE is exactly `1.0f` (0x3f800000),
   i.e. the shipped 4.10 does the same.  Consequence: `RunMissions`
   (@0044f344, structurally identical to the RP donor) finds
   `Now() >= end_of_frame` after every single background pass —
   **exactly one background slot per loop frame**, ours and shipped.
   Measured: `bg=` grows 1001 per 1001-frame period, every period.

2. **The background slot feeds a 7-task round-robin**
   (`BackgroundTasks::Execute` runs ONE task per call): RoutePacket,
   ProcessEvent, AudioRenderer, GaugeRenderer, NetworkManager,
   CompleteCycles, FryDeathRow.  The gauge renderer gets 1/7th of slots.

3. **The gauge wheel repaints once per pass.**  Each gauge-task slot =
   `ProcessOneActiveGauge()` = ONE active gauge.  When the active list
   is exhausted the renderer enters its `copy` phase (the changed-line
   blit to the display — ~10 extra slots) and only then restarts.
   So per-instrument latency ≈ `7 × (wheel + copy) / loop_fps`.

4. **The wheel is 136 gauges and that is AUTHENTIC.**  BT_GAUGE_LOG
   roster dump: 26 ColorMapperArmor, 12 VertTwoPartBar, 10 LeakGauge,
   8 TwoState/PowerSource/HorizTwoPartBar/CoolingLoop, weapon clusters,
   generator clusters, myomer cluster, pilot list, message board … all
   real cockpit instruments.  A Tesla pod shows every instrument at
   once; nothing pages out.  Do NOT "fix" the roster.

So at our measured ~25–33 loop fps: 7 × 146 / 30 ≈ **34 s** worst-case
per-instrument latency.  That is the operator's symptom, exactly.

## The real defect found: build flags

`build410.sh` compiled with `-O2` alone.  The authentic release tier
(`CODE/BT/OPT.MAK`) is:

    -O2 -Ot -Oc -Og -O -Ol -Z -Ob -Oe -Oi -Om -Op -Ov

(global CSE + global register allocation, invariant code motion, copy
propagation, inline intrinsics, redundant-load suppression, loop opts).
Adopting the full set (all 234 TUs compile clean, no BC4.52 optimizer
ICEs) took the loop from **16.7 → ~30 loop fps wall** on the rig — a
~2× display-cadence improvement for free.  `-w` was kept as `-w-`.
Note: RP-era MAKE.CFG uses `bcc32i` (BC5 toolchain, RP 4.11+); BT 4.10's
OPT.MAK says `BCC = bcc32` — we match 4.10.

## Measurement traps recorded (they cost hours tonight)

- **Incremental-build staging:** the link consumes `build410/lib/*.lib`;
  rebuilding `engine` without `libs` ships STALE members.  Also a
  same-minute mtime tie made the engine step skip freshly patched TUs.
  When probing: `rm` the target objs, then `engine`, `libs`, `link`.
  (l4grend's obj dir is `obj/mungal4` — no underscore.)
- **Guest tick-delta profiling is unreliable in the emulator.**  The SOS
  clock advances in bursts at trap points, so per-stage
  `Now()`-bracket sums measure where the burst LANDS, not cost:
  five timed foreground stages summed 8.7 "ticks/frame" while the whole
  function measured 17.0, with provably empty code between them.
  Wall-clock rates (log-line arrival, fifodump growth) are the only
  trustworthy measure.  The tick probes are compile-gated behind
  `BT_TICK_PROBES` (default OFF); the pure counters (`bg= g= p= c=` on
  the `[stack]` line, BT_STACK_LOG) stay, they never touch the clock.
- **`draw_scene` rate ≠ loop rate.**  The board renderer is
  rate-governed by the RendererManager: 2.9 board-fps while the loop ran
  33 fps.  `fifofps.py` counts true board frames (action 9 records).

## Where the ours-vs-shipped gap stands

fifodump growth mid-mission: shipped ≈ 11.8 KB/s, ours ≈ 4.1 KB/s before
the flag fix, ≈ 6.4 KB/s after.  Byte rate conflates the render governor
with loop rate, so treat as indicative only.  Under `cycles=max` wall
time is trap-dominated; both exes drive the same VPX/serial/AWE devices.

**OPEN QUESTION for the operator:** on THIS RIG, do BTL4OPT's cockpit
instruments visibly update faster than BTL4REC's (post-flag-fix)?  If
yes, the residual is ours-specific guest work and the next tool is a
DOSBox-side sampling profiler (we own the fork) — not more guest
probes.  If no — the rig was always like this and the "original"
baseline was the real pod, whose identical architecture ran at real-
hardware loop rates.

## Probe inventory (all in source410, cheap, env/compile gated)

- `MUNGA/APP.CPP`: counters `bgSlots/bgTaskRuns/gaugeSlices/gaugePasses/
  gaugeCopySlices` + `[stack]` print (env BT_STACK_LOG); tick-delta
  stage/slot timers behind `BT_TICK_PROBES`.
- `MUNGA/APPTASK.CPP` (new shadow, from CODE/RP donor): per-ring-task
  timers behind `BT_TICK_PROBES`.
- `MUNGA/GAUGREND.CPP`: wheel slice/pass counters; one-shot `[roster]`
  dump (env BT_GAUGE_LOG).
- `emulator/render-bridge/fifofps.py`: true board-fps from a fifodump.
- `emulator/render-bridge/pod_render_bgprobe.conf`: clean probe conf
  (BT_STACK_LOG + BT_GAUGE_LOG, no per-frame logs).