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##
## This file is part of the libsigrokdecode project.
##
## Copyright (C) 2016 Anthony Symons <antus@pcmhacking.net>
##
## 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, see <http://www.gnu.org/licenses/>.
##
import sigrokdecode as srd
class SamplerateError(Exception):
pass
def timeuf(t):
return int (t * 1000.0 * 1000.0)
def normalize_time(t):
if t >= 1.0:
return '%d s' % t
elif t >= 0.001:
return '%d ms' % (t * 1000.0)
elif t >= 0.000001:
return '%d μs' % (t * 1000.0 * 1000.0)
elif t >= 0.000000001:
return '%d ns' % (t * 1000.0 * 1000.0 * 1000.0)
else:
return '%f' % t
class Decoder(srd.Decoder):
api_version = 3
id = 'sae_j1850_vpw'
name = 'SAE J1850 VPW'
longname = 'SAE J1850 VPW.'
desc = 'SAE J1850 Variable Pulse Width 1x and 4x.'
license = 'gplv2+'
inputs = ['logic']
outputs = []
tags = ['Automotive']
channels = (
{'id': 'data', 'name': 'Data', 'desc': 'Data line'},
)
annotations = (
('time', 'Time'),
('raw', 'Raw'),
('sof', 'SOF'),
('ifs', 'EOF/IFS'),
('data', 'Data'),
('packet', 'Packet'),
)
annotation_rows = (
('packets', 'Packets', (5,)),
('bytes', 'Bytes', (4,)),
('raws', 'Raws', (1,2,3,)),
('times', 'Times', (0,)),
)
def __init__(self):
self.reset()
def reset(self):
self.state = 'IDLE'
self.samplerate = None
self.byte = 0 # the byte offset in the packet
self.mode = 0 # for by packet decode
self.data = 0 # the current byte
self.datastart = 0 # sample number this byte started at
self.csa = 0 # track the last byte seperately to retrospectively add the CS marker
self.csb = 0
self.count = 0 # which bit number we are up to
self.active = 0 # which logic level is considered active
# vpw timings. ideal, min and max tollerances.
# From SAE J1850 1995 rev section 23.406
self.sof = 200
self.sofl = 164
self.sofh = 245 # 240 by the spec, 245 so a 60us 4x sample will pass
self.long = 128
self.longl = 97
self.longh = 170 # 164 by the spec but 170 for low sample rate tolerance.
self.short = 64
self.shortl = 24 # 35 by the spec, 24 to allow down to 6us as measured in practice for 4x @ 1mhz sampling
self.shorth = 97
self.ifs = 240
self.spd = 1 # set to 4 when a 4x SOF is detected (VPW high speed frame)
def handle_bit(self, ss, es, b):
self.data |= (b << 7-self.count) # MSB-first
self.put(ss, es, self.out_ann, [1, ["%d" % b]])
if self.count == 0:
self.datastart = ss
if self.count == 7:
self.csa = self.datastart # for CS
self.csb = self.samplenum # for CS
self.put(self.datastart, self.samplenum, self.out_ann, [4, ["%02X" % self.data]])
# add protocol parsing here
if self.byte == 0:
self.put(self.datastart, self.samplenum, self.out_ann, [5, ['Priority','Prio','P']])
elif self.byte == 1:
self.put(self.datastart, self.samplenum, self.out_ann, [5, ['Destination','Dest','D']])
elif self.byte == 2:
self.put(self.datastart, self.samplenum, self.out_ann, [5, ['Source','Src','S']])
elif self.byte == 3:
self.put(self.datastart, self.samplenum, self.out_ann, [5, ['Mode','M']])
self.mode = self.data
elif self.mode == 1 and self.byte == 4: # mode 1 payload
self.put(self.datastart, self.samplenum, self.out_ann, [5, ['Pid','P']])
# prepare for next byte
self.count = -1
self.data = 0
self.byte = self.byte + 1 # track packet offset
self.count = self.count + 1
def metadata(self, key, value):
if key == srd.SRD_CONF_SAMPLERATE:
self.samplerate = value
def start(self):
self.out_ann = self.register(srd.OUTPUT_ANN)
def decode(self):
if not self.samplerate:
raise SamplerateError('Cannot decode without samplerate.')
self.wait({0: 'e'})
es = self.samplenum
while True:
ss = es
pin, = self.wait({0: 'e'})
es = self.samplenum
samples = es - ss
txt = normalize_time(samples / self.samplerate)
self.put(ss, es, self.out_ann, [0, [txt]])
t = timeuf(samples / self.samplerate)
if self.state == 'IDLE': # detect and set speed from the size of sof
if pin == self.active and t in range(self.sofl , self.sofh):
self.put(ss, es, self.out_ann, [1, ['1X SOF', 'S1', 'S']])
self.spd = 1
self.data = 0
self.count = 0
self.state = 'DATA'
elif pin == self.active and t in range(int(self.sofl / 4) , int(self.sofh / 4)):
self.put(ss, es, self.out_ann, [1, ['4X SOF', 'S4', '4']])
self.spd = 4
self.data = 0
self.count = 0
self.state = 'DATA'
elif self.state == 'DATA':
if t >= int(self.ifs / self.spd):
self.state = 'IDLE'
self.put(ss, es, self.out_ann, [1, ["EOF/IFS", "E"]]) # EOF=239-280 IFS=281+
self.put(self.csa, self.csb, self.out_ann, [5, ['Checksum','CS','C']]) # retrospective print of CS
self.byte = 0 # reset packet offset
elif t in range(int(self.shortl / self.spd), int(self.shorth / self.spd)):
if pin == self.active:
self.handle_bit(ss, es, 1)
else:
self.handle_bit(ss, es, 0)
elif t in range(int(self.longl / self.spd), int(self.longh / self.spd)):
if pin == self.active:
self.handle_bit(ss, es, 0)
else:
self.handle_bit(ss, es, 1)
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