LASER_PWM waveform gate PASSED - scope-verified on the physical pin

Direct PWMSAR duty steps with the machine in the locked state (controller stopped, cnc disabled so steppers are unpowered, laser latch locked, lid closed; laser_on_sampled stayed 0 throughout). Measured on the pin: 25.0 us period / 40 kHz stable across the full duty range; 50/25/75 percent confirmed visually; low end cursor-measured 6.4 vs 6.3 percent commanded (PWMSAR=8), clean pulse. Matches the register-level audit numbers (divider 13 x 127 counts). Adds pwm_sweep.py / pwm_hold.py to the bench kit and records the two remaining pre-live-fire gates (1-tick laser drop at underrun via the stream path with FIRE observable under a locked latch; interlock readback semantics) in BRINGUP.
2026-09-27 16:51:12 -07:00 · 2026-08-02 16:08:34 -04:00
parent c7e419ff6b
commit fb956971b7
4 changed files with 118 additions and 3 deletions
@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+"""LASER_PWM scope test - runs ON the board.
+
+check: read-only - safety-chain readbacks + PWM2 register dump.
+sweep: step the PWM duty register through known values with pauses so
+       the scope can capture each, then restore the original sample.
+
+The duty register (PWMSAR) is the laser power SETPOINT only. No motion
+subsystem is touched (steppers are disabled before this runs), no
+stream runs, the laser latch is locked, FIRE is never asserted.
+"""
+import mmap, struct, sys, time
+
+PWM2_BASE = 0x02084000
+PERCLK_HZ = 66_000_000
+SAR_OFF = 0x0C
+
+
+def rd(name):
+    try:
+        with open('/sys/glowforge/' + name) as f:
+            return f.read().strip()
+    except OSError as e:
+        return '<%s>' % e
+
+
+def dump_regs(m):
+    cr, sr, ir, sar, pr = struct.unpack('<5I', m[:20])
+    divider = ((cr >> 4) & 0xFFF) + 1
+    counts = pr + 2
+    freq = PERCLK_HZ / (divider * counts) if counts else 0
+    print('PWMCR=0x%08x PWMSAR=%d PWMPR=%d enabled=%s divider=%d counts=%d carrier=%.2f kHz'
+          % (cr, sar, pr, bool(cr & 1), divider, counts, freq / 1000))
+    return sar, pr
+
+
+def safety_readback():
+    print('cnc/state          =', rd('cnc/state'))
+    print('cnc/laser_on       =', rd('cnc/laser_on'))
+    print('cnc/laser_enable   =', rd('cnc/laser_enable'))
+    print('cnc/laser_pgood    =', rd('cnc/laser_pgood'))
+    print('cnc/interlock_circuit =', rd('cnc/interlock_circuit'),
+          '(b0 LASER_ON b1 LASER_ENABLE b2 BUTTON_LATCH b3 LASER_LATCH b4 ILK_RESET)')
+    print('cnc/laser_on_sampled  =', rd('cnc/laser_on_sampled'))
+
+
+mode = sys.argv[1] if len(sys.argv) > 1 else 'check'
+
+with open('/dev/mem', 'r+b') as f:
+    m = mmap.mmap(f.fileno(), 4096, mmap.MAP_SHARED,
+                  mmap.PROT_READ | mmap.PROT_WRITE, offset=PWM2_BASE)
+
+    print('--- safety readback (before)')
+    safety_readback()
+    print('--- PWM2 registers')
+    sar0, pr = dump_regs(m)
+
+    if mode == 'sweep':
+        period = pr + 2
+        steps = [(64, '50%'), (32, '25%'), (96, '75%'), (8, '6%'), (127, '100%')]
+        print('--- duty sweep: 4 s per step, watch the scope')
+        for sar, label in steps:
+            m[SAR_OFF:SAR_OFF + 4] = struct.pack('<I', sar)
+            time.sleep(0.1)
+            cur = struct.unpack('<I', m[SAR_OFF:SAR_OFF + 4])[0]
+            print('  PWMSAR=%-3d (%s of %d counts)  readback=%d' % (sar, label, period, cur))
+            time.sleep(4)
+        m[SAR_OFF:SAR_OFF + 4] = struct.pack('<I', sar0)
+        print('--- restored PWMSAR=%d' % sar0)
+        print('--- safety readback (after)')
+        safety_readback()
+        dump_regs(m)
+
+    m.close()