Real digital storage scopes have a trigger that pins the visible window
around a detected edge — without it, sparse activity (UART bytes once
per loop, an interrupt firing every few seconds) scrolls off the screen
faster than the eye can catch. Velxio's scope was free-running only,
which made the recent UART TX waveform work effectively invisible at
fine time/div settings: the byte burst was 87 µs but the window only
showed the most recent 1 ms.
Three trigger modes, matching what you'd find on a Rigol / Tektronix:
* Auto — current free-running behaviour, window's right edge
tracks the most recent sample. Default.
* Normal — window pins around each triggering edge so the event
lands at `triggerPosition * windowMs` from the left
(default centred at 0.5). Keeps re-pinning on every
new triggering edge.
* Single — arms once, freezes the trace on the first triggering
edge by flipping `running = false`. User clicks
"Re-arm" to capture again.
Three knobs configurable per mode:
- source: which channel produces the trigger event
- edge: rising (↑) / falling (↓) / either (⇅)
- position: trigger lands at this fraction of the window
(UI hard-codes centre 0.5 for now; the store field
accepts any value if we want a draggable handle later)
UI additions in the scope header (only shown when mode != auto):
- source / edge dropdowns
- status badge (Armed / Triggered / Captured) with pulse animation
on Armed so the user knows the scope is waiting for an event
- Re-arm button in Single mode after capture
Canvas changes:
- Dashed orange "T" marker drawn at the trigger position when an
edge is latched and within the visible window.
Store changes:
- pushSample peeks at the trigger channel's previous state, detects
a matching edge, sets triggeredAtMs (and stops `running` for
Single mode). matchesTriggerEdge() exported for unit testing.
- clearSamples / setTriggerMode / setTriggerChannel / setTriggerEdge
all re-arm the trigger; rearmTrigger() explicitly resets and resumes
capture (used by the Re-arm button after a single-shot).
Covered by 11 new vitest cases (oscilloscope-trigger.test.ts) plus the
existing 1892 tests still pass.
Closes the "I set 0.1 ms/div on a Serial.print sketch and see a flat
line" UX trap reported on the Discord follow-up — at 0.1 ms/div the
window is 1 ms but bytes fire every 2 s, so without a trigger the
chance of catching the burst is < 0.05 %. With Normal trigger on
rising D1 the burst pins in the middle of the window and the user can
zoom down to bit level (8.68 µs each) without losing it.
David Montero