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##
## This file is part of the libsigrokdecode project.
##
## Copyright (C) 2012-2013 Uwe Hermann <uwe@hermann-uwe.de>
##
## This program is free software; you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation; either version 2 of the License, or
## (at your option) any later version.
##
## This program is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with this program; if not, write to the Free Software
## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
##
# CAN protocol decoder
import sigrokdecode as srd
class Decoder(srd.Decoder):
api_version = 1
id = 'can'
name = 'CAN'
longname = 'Controller Area Network'
desc = 'Field bus protocol for distributed realtime control.'
license = 'gplv2+'
inputs = ['logic']
outputs = ['can']
probes = [
{'id': 'can_rx', 'name': 'CAN RX', 'desc': 'CAN bus line'},
]
optional_probes = []
options = {
'bitrate': ['Bitrate', 1000000], # 1Mbit/s
'sample_point': ['Sample point', 70], # 70%
}
annotations = [
['Text', 'Human-readable text'],
['Warnings', 'Human-readable warnings'],
]
def __init__(self, **kwargs):
self.reset_variables()
def start(self, metadata):
# self.out_proto = self.add(srd.OUTPUT_PROTO, 'can')
self.out_ann = self.add(srd.OUTPUT_ANN, 'can')
self.samplerate = metadata['samplerate']
self.bit_width = float(self.samplerate) / float(self.options['bitrate'])
self.bitpos = (self.bit_width / 100.0) * self.options['sample_point']
def report(self):
pass
def putx(self, data):
self.put(self.samplenum, self.samplenum, self.out_ann, data)
def reset_variables(self):
self.state = 'IDLE'
self.sof = self.frame_type = self.dlc = None
self.rawbits = [] # All bits, including stuff bits
self.bits = [] # Only actual CAN frame bits (no stuff bits)
self.curbit = 0 # Current bit of CAN frame (bit 0 == SOF)
self.last_databit = 999 # Positive value that bitnum+x will never match
# Return True if we reached the desired bit position, False otherwise.
def reached_bit(self, bitnum):
bitpos = int(self.sof + (self.bit_width * bitnum) + self.bitpos)
if self.samplenum >= bitpos:
return True
return False
def is_stuff_bit(self):
# CAN uses NRZ encoding and bit stuffing.
# After 5 identical bits, a stuff bit of opposite value is added.
last_6_bits = self.rawbits[-6:]
if last_6_bits not in ([0, 0, 0, 0, 0, 1], [1, 1, 1, 1, 1, 0]):
return False
# Stuff bit. Keep it in self.rawbits, but drop it from self.bits.
self.putx([0, ['Stuff bit: %d' % self.rawbits[-1]]])
self.bits.pop() # Drop last bit.
return True
def is_valid_crc(self, crc_bits):
return True # TODO
def decode_error_frame(self, bits):
pass # TODO
def decode_overload_frame(self, bits):
pass # TODO
# Both standard and extended frames end with CRC, CRC delimiter, ACK,
# ACK delimiter, and EOF fields. Handle them in a common function.
# Returns True if the frame ended (EOF), False otherwise.
def decode_frame_end(self, can_rx, bitnum):
# CRC sequence (15 bits)
if bitnum == (self.last_databit + 15):
x = self.last_databit + 1
crc_bits = self.bits[x:x + 15 + 1]
self.crc = int(''.join(str(d) for d in crc_bits), 2)
self.putx([0, ['CRC: 0x%04x' % self.crc]])
if not self.is_valid_crc(crc_bits):
self.putx([0, ['CRC is invalid']])
# CRC delimiter bit (recessive)
elif bitnum == (self.last_databit + 16):
self.putx([0, ['CRC delimiter: %d' % can_rx]])
# ACK slot bit (dominant: ACK, recessive: NACK)
elif bitnum == (self.last_databit + 17):
ack = 'ACK' if can_rx == 0 else 'NACK'
self.putx([0, ['ACK slot: %s' % ack]])
# ACK delimiter bit (recessive)
elif bitnum == (self.last_databit + 18):
self.putx([0, ['ACK delimiter: %d' % can_rx]])
# End of frame (EOF), 7 recessive bits
elif bitnum == (self.last_databit + 25):
self.putx([0, ['End of frame', 'EOF']])
self.reset_variables()
return True
return False
# Returns True if the frame ended (EOF), False otherwise.
def decode_standard_frame(self, can_rx, bitnum):
# Bit 14: RB0 (reserved bit)
# Has to be sent dominant, but receivers should accept recessive too.
if bitnum == 14:
self.putx([0, ['RB0: %d' % can_rx]])
# Bit 12: Remote transmission request (RTR) bit
# Data frame: dominant, remote frame: recessive
# Remote frames do not contain a data field.
rtr = 'remote' if self.bits[12] == 1 else 'data'
self.putx([0, ['RTR: %s frame' % rtr]])
# Bits 15-18: Data length code (DLC), in number of bytes (0-8).
elif bitnum == 18:
self.dlc = int(''.join(str(d) for d in self.bits[15:18 + 1]), 2)
self.putx([0, ['DLC: %d' % self.dlc]])
self.last_databit = 18 + (self.dlc * 8)
# Bits 19-X: Data field (0-8 bytes, depending on DLC)
# The bits within a data byte are transferred MSB-first.
elif bitnum == self.last_databit:
for i in range(self.dlc):
x = 18 + (8 * i) + 1
b = int(''.join(str(d) for d in self.bits[x:x + 8]), 2)
self.putx([0, ['Data byte %d: 0x%02x' % (i, b)]])
elif bitnum > self.last_databit:
return self.decode_frame_end(can_rx, bitnum)
return False
# Returns True if the frame ended (EOF), False otherwise.
def decode_extended_frame(self, can_rx, bitnum):
# Bits 14-31: Extended identifier (EID[17..0])
if bitnum == 31:
self.eid = int(''.join(str(d) for d in self.bits[14:]), 2)
self.putx([0, ['Extended ID: %d (0x%x)' % (self.eid, self.eid)]])
self.fullid = self.id << 18 | self.eid
self.putx([0, ['Full ID: %d (0x%x)' % (self.fullid, self.fullid)]])
# Bit 12: Substitute remote request (SRR) bit
self.putx([0, ['SRR: %d' % self.bits[12]]])
# Bit 32: Remote transmission request (RTR) bit
# Data frame: dominant, remote frame: recessive
# Remote frames do not contain a data field.
if bitnum == 32:
rtr = 'remote' if can_rx == 1 else 'data'
self.putx([0, ['RTR: %s frame' % rtr]])
# Bit 33: RB1 (reserved bit)
elif bitnum == 33:
self.putx([0, ['RB1: %d' % can_rx]])
# Bit 34: RB0 (reserved bit)
elif bitnum == 34:
self.putx([0, ['RB0: %d' % can_rx]])
# Bits 35-38: Data length code (DLC), in number of bytes (0-8).
elif bitnum == 38:
self.dlc = int(''.join(str(d) for d in self.bits[35:38 + 1]), 2)
self.putx([0, ['DLC: %d' % self.dlc]])
self.last_databit = 38 + (self.dlc * 8)
# Bits 39-X: Data field (0-8 bytes, depending on DLC)
# The bits within a data byte are transferred MSB-first.
elif bitnum == self.last_databit:
for i in range(self.dlc):
x = 38 + (8 * i) + 1
b = int(''.join(str(d) for d in self.bits[x:x + 8]), 2)
self.putx([0, ['Data byte %d: 0x%02x' % (i, b)]])
elif bitnum > self.last_databit:
return self.decode_frame_end(can_rx, bitnum)
return False
def handle_bit(self, can_rx):
self.rawbits.append(can_rx)
self.bits.append(can_rx)
# Get the index of the current CAN frame bit (without stuff bits).
bitnum = len(self.bits) - 1
# For debugging.
# self.putx([0, ['Bit %d (CAN bit %d): %d' % \
# (self.curbit, bitnum, can_rx)]])
# If this is a stuff bit, remove it from self.bits and ignore it.
if self.is_stuff_bit():
self.curbit += 1 # Increase self.curbit (bitnum is not affected).
return
# Bit 0: Start of frame (SOF) bit
if bitnum == 0:
if can_rx == 0:
self.putx([0, ['Start of frame', 'SOF']])
else:
self.putx([1, ['Start of frame (SOF) must be a dominant bit']])
# Bits 1-11: Identifier (ID[10..0])
# The bits ID[10..4] must NOT be all recessive.
elif bitnum == 11:
self.id = int(''.join(str(d) for d in self.bits[1:]), 2)
self.putx([0, ['ID: %d (0x%x)' % (self.id, self.id)]])
# RTR or SRR bit, depending on frame type (gets handled later).
elif bitnum == 12:
# self.putx([0, ['RTR/SRR: %d' % can_rx]])
pass
# Bit 13: Identifier extension (IDE) bit
# Standard frame: dominant, extended frame: recessive
elif bitnum == 13:
ide = self.frame_type = 'standard' if can_rx == 0 else 'extended'
self.putx([0, ['IDE: %s frame' % ide]])
# Bits 14-X: Frame-type dependent, passed to the resp. handlers.
elif bitnum >= 14:
if self.frame_type == 'standard':
done = self.decode_standard_frame(can_rx, bitnum)
else:
done = self.decode_extended_frame(can_rx, bitnum)
# The handlers return True if a frame ended (EOF).
if done:
return
# After a frame there are 3 intermission bits (recessive).
# After these bits, the bus is considered free.
self.curbit += 1
def decode(self, ss, es, data):
for (self.samplenum, pins) in data:
(can_rx,) = pins
# State machine.
if self.state == 'IDLE':
# Wait for a dominant state (logic 0) on the bus.
if can_rx == 1:
continue
self.sof = self.samplenum
# self.putx([0, ['SOF']])
self.state = 'GET BITS'
elif self.state == 'GET BITS':
# Wait until we're in the correct bit/sampling position.
if not self.reached_bit(self.curbit):
continue
self.handle_bit(can_rx)
else:
raise Exception("Invalid state: %s" % self.state)
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