Scroll speeds are solved against display.hardware.limit_refresh_rate_hz,
which is only a ceiling. A panel that cannot reach it still moves whole
pixels per frame, but every scroll runs slow by the shortfall and the
"smooth" ladder is the cap's, not the panel's. A user rig (Pi 4, 2x128x64,
adafruit-hat-pwm, pwm_bits 9, gpio_slowdown 5) measured 107.6-113.1 Hz under
a 120 Hz cap: 60 px/s ran at 55, and nothing said why.
- scroll_config: refresh_shortfall() (more than 3% under the planned rate),
holdable_cap() (a multiple of 10, 5% under the measurement, since the
measurement is the fast end of an uncapped panel's drift), and
describe_refresh_shortfall().
- FrameTimingRecorder.plan_refresh(): once the measured period has held for
three trusted windows, a shortfall is logged once as a warning naming the
cap to use. DisplayManager calls it only for a real panel, not the
emulator or the fallback canvas. The stats file records
planned_refresh_hz (additive).
- GET /api/v3/config/refresh-rate, plus a hint under the Display tab's
Limit Refresh Rate field with a button that fills in the suggested cap.
- _panel_refresh_hz (behind the Vegas slider's advice) ignores a measurement
written under a different cap, so a changed cap stops being advised from
the old rate before the display restarts.
Verified on ledpi with a temporary 200 Hz cap: the warning logged about a
minute after the restart ("about 132 Hz ... Set Limit Refresh Rate to
120 Hz"), the endpoint returned the same shortfall, and the Display tab
showed the hint; its button filled in 120. ledpi was restored afterwards.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A collection during interpreter shutdown called GcMonitor after the
module's `time` global was torn down, printing "Exception ignored while
calling GC callback ... 'NoneType' object has no attribute
'perf_counter'" at the end of service and test runs.
- GcMonitor binds its clock and sys.is_finalizing at construction and
does nothing once the interpreter is finalizing.
- install_gc_monitor() unregisters it with atexit; new
uninstall_gc_monitor().
- DisplayManager.cleanup() (reached from SIGTERM via run()'s finally)
unregisters it alongside the frame recorder.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
A GcMonitor in src/common/frame_timing.py, installed once per process from gc.callbacks by the display manager (and render_bench), counts collections and seconds per generation, the longest, and those of 20 ms or more. A long one tags the next presented frame 'gc' in record(), so frame_soak shows its late rate under 'after work'; the stats file gains an additive 'gc' block printed as a 'Garbage collection' line; and a Render stall dump says when a long collection ran inside the stall. Diagnostic only: nothing tunes, freezes or disables the collector.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A static plugin screen that follows a scroller no longer starts with the ticker's lagging rows on scan-compensated panels, and the 1 Hz loop's second frame is no longer recorded as a ~1 s mid-scroll freeze / Render stall. The display controller calls DisplayManager.end_scroll_for_static_screen() before a static screen's first display() (clears the scan history; _scan_segments passes its frames through in one swap) and set_scrolling_state(False) after it; the scroller's hold stays until then, so late-frame counts are unchanged. A screen's first frame is tagged 'handover': gaps of 250 ms or more before it go to the additive handover_freezes (frame_soak prints 'Handover gaps'), not freezes. The display thread is named display-<plugin id>. The WiFi notice and the schedule-off blank are not covered yet (docs list them as a follow-up).
ledpi A B B A soak (20 min each, --preview): main 0.118% / 0.113% late with 6 / 3 freezes; with this and #717 0.107% / 0.104% late, 0 freezes.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
src/common/frame_timing.py times every frame the display presents, whoever drew it, and writes cumulative counters to /dev/shm. scripts/frame_soak.py grades a running service (late frames, freezes, where the time goes) and scripts/render_bench.py the hardware and render path alone. A stall watchdog logs the stacks behind any scroll held up for 250 ms or more (LEDMATRIX_STALL_WATCHDOG_MS lowers that). See docs/SCROLL_PERFORMANCE.md, "Soaking a rig".
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
