From 4c6cca15112c5b70e0686dc68a5751920bd7cf8f Mon Sep 17 00:00:00 2001 From: ScottW514 Date: Sun, 2 Aug 2026 17:20:57 -0400 Subject: [PATCH] BRINGUP: homing design decided - accel bump-detect, soft-bump fallback No factory X/Y home switches (unpopulated IO header only). Current sensing is a dead end (PIC attrs are setpoints; stalled steppers do not draw more current). Primary: head lis2hh12 accelerometer contact detection (needs IIO bring-up). Fallback: low-current soft-bump against the hard stops. Camera homing stays a future option. --- docs/BRINGUP.md | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/docs/BRINGUP.md b/docs/BRINGUP.md index fb8923f..8a794bb 100644 --- a/docs/BRINGUP.md +++ b/docs/BRINGUP.md @@ -234,9 +234,24 @@ hardware I/O — host testing). `_config_from_pulse` scheme. - **Interlock readback semantics cross-check: OPEN** (see factory-laser-safety-readbacks notes). -3. **Homing**: X/Y home switch GPIOs exist in the cnc pin map (unused so - far); wire as grblHAL limits or keep StallGuard-less factory scheme; - Z homes against the hall sensor (top). +3. **Homing (design decided 2026-08-02)**: the factory machine has NO + X/Y home switches (only an unpopulated IO header — hardware project + for another day). Current-spike stall sensing is a dead end (the PIC + current attrs are setpoints, not measurements, and chopper-driven + steppers don't draw more current when stalled). Plan, simple first: + 1. **Primary: accelerometer bump-detect** — the head lis2hh12 (in + the DT, `head/accel_irq` readback) senses the contact jolt while + creeping toward the corner; stop, back off, zero. Needs IIO + bring-up on the dev image. + 2. **Fallback: soft-bump** — PIC current dropped to a weak value, + slow constant-velocity stream past full travel, harmless step + skipping against the hard stop, back off, zero counters, restore + run current. Zero new sensing; ~±1 full step (0.15 mm) + repeatability; brief grind during the skip. Y "weak" value needs + empirical tuning (factory run is already only 22). + Camera homing (the factory's actual method) is a future option once + the camera service exists. Z homes against the hall sensor (top), + hall-supervised only. 4. **6.5 safety mapping**: door/estop evdev → feed-hold/halt in the backend; underrun → grblHAL alarm; interlock-trip recovery check. 5. **6.6 camera service**: persistent MJPEG (ulfius, forgectrl) — also the