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Automatically fix the frame FCS in bellows dump #428

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Merged
Adminiuga merged 3 commits into from
Jul 25, 2021
Merged

Automatically fix the frame FCS in bellows dump #428

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d4849f2
Automatically fix the frame FCS in `bellows dump`
puddly Jul 22, 2021
74c5ce1
Decrease logging level and only fix FCS when it's 0x000F
puddly Jul 24, 2021
8cb873b
Update bellows/cli/dump.py
Adminiuga Jul 25, 2021
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25 changes: 25 additions & 0 deletions bellows/cli/dump.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import asyncio
import logging
import time

import click
Expand All @@ -7,6 +8,8 @@
from . import util
from .main import main

LOGGER = logging.getLogger(__name__)


@main.command()
@click.option(
Expand Down Expand Up @@ -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
Expand All @@ -60,6 +77,14 @@ async def _dump(ctx, channel, outfile):
def cb(frame_name, response):
if frame_name == "mfglibRxHandler":
data = response[2]

# Later releases of EmberZNet incorrectly use a static FCS
fcs = data[-2:]
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

ts = time.time()
ts_sec = int(ts)
ts_usec = int((ts - ts_sec) * 1000000)
Expand Down