Homing spike: accelerometer bump-detect proven on hardware

The head lis2hh12 (i2c-3 0x1e, direct-I2C at ~530 Hz - st_accel sysfs one-shots are ~6 Hz and the kernel has no IIO triggers) sees rail contact as a 20-40x jolt over the creep baseline within ~4 ms. bump_seek.py: 3/3 detected hits, zero false positives over ~180 mm of creep, jog-cancel stop and back-off. BRINGUP carries the full record and the driver integration design.

scripts/bench/accel_fast.py

@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+"""Fast direct-I2C sampler for the two LIS2HH12s on the head bus (i2c-3).
+
+Unbinds st_accel from both for the capture (rebinds after), programs
+800 Hz ODR, and polls OUT_X..OUT_Z as fast as the bus allows.
+
+Usage: accel_fast.py <seconds> [jog-gcode [jog2-gcode]]
+Jogs are sent to the local grblHAL at t=2 s (and t=2+4 s for jog2).
+CSV to /tmp/accel.csv: t,addr,x,y,z
+"""
+import fcntl
+import os
+import socket
+import struct
+import sys
+import time
+
+I2C_SLAVE = 0x0703
+BUS = '/dev/i2c-3'
+ADDRS = [0x1e, 0x1d]
+WHO_AM_I = 0x0F
+CTRL1 = 0x20
+OUT_X_L = 0x28
+
+DRIVER = '/sys/bus/i2c/drivers/st-accel-i2c'
+
+
+def bind_ctl(op, dev):
+    try:
+        with open(DRIVER + '/' + op, 'w') as f:
+            f.write(dev)
+    except OSError:
+        pass
+
+
+def main():
+    dur = float(sys.argv[1]) if len(sys.argv) > 1 else 5.0
+    jogs = sys.argv[2:4]
+
+    for a in ADDRS:
+        bind_ctl('unbind', '3-%04x' % a)
+
+    fd = os.open(BUS, os.O_RDWR)
+    for a in ADDRS:
+        fcntl.ioctl(fd, I2C_SLAVE, a)
+        os.write(fd, bytes([WHO_AM_I]))
+        who = os.read(fd, 1)[0]
+        os.write(fd, bytes([CTRL1, 0x6F]))   # 800 Hz, BDU, XYZ on
+        print('addr 0x%02x WHO_AM_I=0x%02x' % (a, who))
+    time.sleep(0.05)
+
+    sock = None
+    if jogs:
+        sock = socket.create_connection(('127.0.0.1', 23), timeout=3)
+        sock.settimeout(0.1)
+
+    out = open('/tmp/accel.csv', 'w')
+    t0 = time.monotonic()
+    sent = 0
+    n = 0
+    while True:
+        t = time.monotonic() - t0
+        if t > dur:
+            break
+        if sock and sent < len(jogs) and t > 2.0 + 4.0 * sent:
+            sock.sendall((jogs[sent] + '\n').encode())
+            sent += 1
+        for a in ADDRS:
+            fcntl.ioctl(fd, I2C_SLAVE, a)
+            os.write(fd, bytes([OUT_X_L]))
+            d = os.read(fd, 6)
+            x, y, z = struct.unpack('<hhh', d)
+            out.write('%.5f,%02x,%d,%d,%d\n' % (t, a, x, y, z))
+            n += 1
+    out.close()
+    if sock:
+        try:
+            sock.recv(4096)
+        except OSError:
+            pass
+        sock.close()
+    os.close(fd)
+
+    for a in ADDRS:
+        bind_ctl('bind', '3-%04x' % a)
+    print('samples:', n, 'rate: %.0f Hz per device' % (n / 2 / dur))
+
+
+if __name__ == '__main__':
+    main()