DSView/libsigrokdecode4DSL/decoders/sae_j1850_vpw/pd.py

##
## 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)

class Ann:
    ANN_RAW, ANN_SOF, ANN_IFS, ANN_DATA, \
    ANN_PACKET = range(5)

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', 'idn':'dec_sae_j1850_vpw_chan_data'},
    )
    annotations = (
        ('raw', 'Raw'),
        ('sof', 'SOF'),
        ('ifs', 'EOF/IFS'),
        ('data', 'Data'),
        ('packet', 'Packet'),
    )
    annotation_rows = (
        ('raws', 'Raws', (Ann.ANN_RAW, Ann.ANN_SOF, Ann.ANN_IFS,)),
        ('bytes', 'Bytes', (Ann.ANN_DATA,)),
        ('packets', 'Packets', (Ann.ANN_PACKET,)),
    )

    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, [Ann.ANN_RAW, ["%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, [Ann.ANN_DATA, ["%02X" % self.data]])
            # add protocol parsing here
            if self.byte == 0:
                self.put(self.datastart, self.samplenum, self.out_ann, [Ann.ANN_PACKET, ['Priority','Prio','P']])
            elif self.byte == 1:
                self.put(self.datastart, self.samplenum, self.out_ann, [Ann.ANN_PACKET, ['Destination','Dest','D']])
            elif self.byte == 2:
                self.put(self.datastart, self.samplenum, self.out_ann, [Ann.ANN_PACKET, ['Source','Src','S']])
            elif self.byte == 3:
                self.put(self.datastart, self.samplenum, self.out_ann, [Ann.ANN_PACKET, ['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, [Ann.ANN_PACKET, ['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
            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, [Ann.ANN_RAW, ['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, [Ann.ANN_RAW, ['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, [Ann.ANN_RAW, ["EOF/IFS", "E"]]) # EOF=239-280 IFS=281+
                    self.put(self.csa, self.csb, self.out_ann, [Ann.ANN_PACKET, ['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)