vpw: introduce SAE J1850 (VPW) decoder

Introduce a protocol decoder for the GM VPW 1x and 4x Vehicle Bus
(SAE J1850, or VPW for variable pulse width).

2 files changed, 209 insertions, 0 deletions

diff --git a/decoders/vpw/__init__.py b/decoders/vpw/__init__.py
new file mode 100644
index 0000000..4667efa
--- /dev/null
+++ b/decoders/vpw/__init__.py
@@ -0,0 +1,25 @@
+##
+## 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, write to the Free Software
+## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+##
+
+'''
+VPW decoder, Decode GM VPW 1X and 4X Vehicle Bus
+'''
+
+from .pd import Decoder
diff --git a/decoders/vpw/pd.py b/decoders/vpw/pd.py
new file mode 100644
index 0000000..a1dd8ec
--- /dev/null
+++ b/decoders/vpw/pd.py
@@ -0,0 +1,184 @@
+##
+## 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, write to the Free Software
+## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+##
+
+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 = 2
+    id = 'vpw'
+    name = 'VPW'
+    longname = 'J1850 VPW Decoder'
+    desc = 'Decode J1850 VPW 1x and 4x'
+    license = 'gplv2+'
+    inputs = ['logic']
+    outputs = ['timing']
+    channels = (
+        {'id': 'data', 'name': 'Data', 'desc': 'Data line'},
+    )
+    annotations = (
+        ('time', 'Time'),
+        ('raw', 'Raw'),
+        ('sof', 'SOF'),
+        ('ifs', 'EOF/IFS'),
+        ('data', 'Data'),
+        ('packet', 'Packet'),
+    )
+    annotation_rows = (
+        ('packet', 'Packet', (5,)),
+        ('byte', 'Byte', (4,)),
+        ('raw', 'Raw', (1,2,3,)),
+        ('time', 'Time', (0,)),
+    )
+
+    def __init__(self, **kwargs):
+        self.state = 'IDLE'
+        self.samplerate = None
+        self.oldpin = None
+        self.last_samplenum = 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, b):
+        self.data |= (b << 7-self.count) # MSB-first
+        self.put(self.last_samplenum, self.samplenum, self.out_ann, [1, ["%d" % b]])
+        if self.count == 0:
+            self.datastart = self.last_samplenum
+        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, ss, es, data):
+        if not self.samplerate:
+            raise SamplerateError('Cannot decode without samplerate.')
+
+        for (self.samplenum, (pin,)) in data:
+            # Ignore identical samples early on (for performance reasons).
+            if self.oldpin == pin:
+                continue
+
+            if self.oldpin is None:
+                self.oldpin = pin
+                self.last_samplenum = self.samplenum
+                continue
+
+            if self.oldpin != pin:
+                samples = self.samplenum - self.last_samplenum
+                txt=normalize_time(samples / self.samplerate)
+                self.put(self.last_samplenum, self.samplenum, 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(self.last_samplenum, self.samplenum, 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(self.last_samplenum, self.samplenum, 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(self.last_samplenum, self.samplenum, 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(1)
+                        else:
+                            self.handle_bit(0)
+                    elif t in range(int(self.longl/self.spd), int(self.longh/self.spd)):
+                        if pin==self.active:
+                            self.handle_bit(0)
+                        else:
+                            self.handle_bit(1)
+
+                # Store data for next round.
+                self.last_samplenum = self.samplenum
+                self.oldpin = pin