From d4849f213fa3e9330fb967c87e597c24524d0e95 Mon Sep 17 00:00:00 2001
From: puddly <32534428+puddly@users.noreply.github.com>
Date: Thu, 22 Jul 2021 16:22:42 -0400
Subject: [PATCH 1/3] Automatically fix the frame FCS in `bellows dump`

---
 bellows/cli/dump.py | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/bellows/cli/dump.py b/bellows/cli/dump.py
index 5dcf8702..a6ec4f6e 100644
--- a/bellows/cli/dump.py
+++ b/bellows/cli/dump.py
@@ -1,4 +1,5 @@
 import asyncio
+import logging
 import time
 
 import click
@@ -7,6 +8,8 @@
 from . import util
 from .main import main
 
+LOGGER = logging.getLogger(__name__)
+
 
 @main.command()
 @click.option(
@@ -39,6 +42,20 @@ def dump(ctx, channel, outfile):
             ctx.obj["ezsp"].close()
 
 
+def ieee_15_4_fcs(data: bytes) -> bytes:
+    # Modified from the implementation in `scapy.layers.dot15d4:Dot15d4FCS.compute_fcs`
+    crc = 0x0000
+
+    for c in data:
+        q = (crc ^ c) & 15  # Do low-order 4 bits
+        crc = (crc // 16) ^ (q * 0x1081)
+
+        q = (crc ^ (c // 16)) & 15  # And high 4 bits
+        crc = (crc // 16) ^ (q * 0x1081)
+
+    return crc.to_bytes(2, "little")
+
+
 async def _dump(ctx, channel, outfile):
     s = await util.setup(ctx.obj["device"], ctx.obj["baudrate"])
     ctx.obj["ezsp"] = s
@@ -60,6 +77,12 @@ async def _dump(ctx, channel, outfile):
     def cb(frame_name, response):
         if frame_name == "mfglibRxHandler":
             data = response[2]
+            fcs = ieee_15_4_fcs(data[0:-2])
+
+            if data[-2:] != fcs:
+                LOGGER.warning("Fixing frame FCS (expected %s, got %s)", fcs, data[-2:])
+                data = data[0:-2] + fcs
+
             ts = time.time()
             ts_sec = int(ts)
             ts_usec = int((ts - ts_sec) * 1000000)

From 74c5ce1004b0912ec15ca3dd29d7760083b5e2b2 Mon Sep 17 00:00:00 2001
From: puddly <32534428+puddly@users.noreply.github.com>
Date: Sat, 24 Jul 2021 14:22:10 -0400
Subject: [PATCH 2/3] Decrease logging level and only fix FCS when it's 0x000F

---
 bellows/cli/dump.py | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/bellows/cli/dump.py b/bellows/cli/dump.py
index a6ec4f6e..f55d45ec 100644
--- a/bellows/cli/dump.py
+++ b/bellows/cli/dump.py
@@ -77,11 +77,14 @@ async def _dump(ctx, channel, outfile):
     def cb(frame_name, response):
         if frame_name == "mfglibRxHandler":
             data = response[2]
-            fcs = ieee_15_4_fcs(data[0:-2])
 
-            if data[-2:] != fcs:
-                LOGGER.warning("Fixing frame FCS (expected %s, got %s)", fcs, data[-2:])
-                data = data[0:-2] + fcs
+            # Later releases of EmberZNet incorrectly use a static FCS
+            fcs = data[-2:]
+            computed_fcs = ieee_15_4_fcs(data[0:-2])
+
+            if s.ezsp_version == 8 and fcs == b"\x0F\x00" and fcs != computed_fcs:
+                LOGGER.debug("Fixing FCS (expected %s, got %s)", computed_fcs, fcs)
+                data = data[0:-2] + computed_fcs
 
             ts = time.time()
             ts_sec = int(ts)

From 8cb873bc8ed267b8187ac4d89b562b90c19cb2ba Mon Sep 17 00:00:00 2001
From: Alexei Chetroi <lexoid@gmail.com>
Date: Sat, 24 Jul 2021 22:04:03 -0400
Subject: [PATCH 3/3] Update bellows/cli/dump.py

---
 bellows/cli/dump.py | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/bellows/cli/dump.py b/bellows/cli/dump.py
index f55d45ec..a9415e70 100644
--- a/bellows/cli/dump.py
+++ b/bellows/cli/dump.py
@@ -80,9 +80,8 @@ def cb(frame_name, response):
 
             # Later releases of EmberZNet incorrectly use a static FCS
             fcs = data[-2:]
-            computed_fcs = ieee_15_4_fcs(data[0:-2])
-
-            if s.ezsp_version == 8 and fcs == b"\x0F\x00" and fcs != computed_fcs:
+            if s.ezsp_version == 8 and fcs == b"\x0F\x00":
+                computed_fcs = ieee_15_4_fcs(data[0:-2])
                 LOGGER.debug("Fixing FCS (expected %s, got %s)", computed_fcs, fcs)
                 data = data[0:-2] + computed_fcs