cart_firmware_added

device_firmware/cart_firmware/tools/decode.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+"""Decode a captured frame as SBUS: UART 100 kbit/s 8E2, 25-byte frame,
+16 channels x 11 bits.
+
+Usage: .venv/bin/python tools/decode.py captures/<name>.npz
+"""
+import sys
+
+import numpy as np
+
+BIT_US = 10.0
+
+path = sys.argv[1]
+d = np.load(path)
+volts = d["volts"]
+srate = float(d["srate"])
+dt_us = 1e6 / srate
+
+# idle level dominates the record; UART logic 1 == idle regardless of
+# physical polarity (this line is standard inverted SBUS: idle low)
+idle = np.median(volts)
+p10, p90 = np.percentile(volts, [10, 90])
+active = p10 if abs(p10 - idle) > abs(p90 - idle) else p90
+thr = (idle + active) / 2
+if active > idle:
+    sig = (volts < thr).astype(np.int8)  # pulses up -> logic 0
+else:
+    sig = (volts > thr).astype(np.int8)
+
+edges = np.flatnonzero(np.diff(sig)) + 1
+starts = np.concatenate(([0], edges))
+ends = np.concatenate((edges, [len(sig)]))
+levels = sig[starts]
+dur_us = (ends - starts) * dt_us
+
+stream = []
+for lv, du in zip(levels[1:-1], dur_us[1:-1]):
+    stream.extend([int(lv)] * max(1, round(du / BIT_US)))
+# trailing idle of last stop bits is trimmed by run cut; pad with idle-high
+stream.extend([1] * 24)
+
+# deframe 8E2: start=0, 8 data LSB-first, even parity, 2 stop=1
+i = 0
+frames = []
+errors = []
+while i + 12 <= len(stream):
+    if stream[i] == 1:
+        i += 1
+        continue
+    data = stream[i + 1 : i + 9]
+    par = stream[i + 9]
+    stops = stream[i + 10 : i + 12]
+    byte = sum(b << k for k, b in enumerate(data))
+    if par != (sum(data) & 1):
+        errors.append((len(frames), "parity"))
+    if stops != [1, 1]:
+        errors.append((len(frames), f"stop={stops}"))
+    frames.append(byte)
+    i += 12
+
+print(f"decoded {len(frames)} bytes, errors: {errors if errors else 'none'}")
+print("hex:", " ".join(f"{b:02X}" for b in frames))
+
+if len(frames) >= 25 and frames[0] == 0x0F:
+    payload = frames[1:23]
+    flags = frames[23]
+    footer = frames[24]
+    bits = 0
+    for k, b in enumerate(payload):
+        bits |= b << (8 * k)
+    ch = [(bits >> (11 * n)) & 0x7FF for n in range(16)]
+    print("\nSBUS frame OK" if footer == 0x00 else f"\nfooter unexpected: {footer:02X}")
+    print("channels:", ch)
+    print(f"flags: 0x{flags:02X} (bit0=ch17 bit1=ch18 bit2=frame_lost bit3=failsafe)")
+else:
+    print("not a valid SBUS frame (no 0x0F header)")