srd: Split USB decoder in two PDs (which stack).

The 'usb_signalling' decoder just decodes symbols from D+/D- levels,
handles bit stuffing and outputs the symbols and (potential) packets.

The 'usb_protocol' decoder takes that output and tried to parse USB
packets from it (SOF, SETUP, IN, OUT, DATA0, and so on).
This is the base decoder on top of which various others will stack
later on.

The two new PDs are work in progress, so we still keep the old 'usb' PD
around for a little while, until the two new ones are fully working and
well-tested.

1 files changed, 146 insertions, 0 deletions

diff --git a/decoders/usb_signalling/usb_signalling.py b/decoders/usb_signalling/usb_signalling.py
new file mode 100644
index 0000000..512703d
--- /dev/null
+++ b/decoders/usb_signalling/usb_signalling.py
@@ -0,0 +1,146 @@
+##
+## This file is part of the sigrok project.
+##
+## Copyright (C) 2011 Gareth McMullin <gareth@blacksphere.co.nz>
+## Copyright (C) 2012 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
+##
+
+# USB signalling (low-speed and full-speed) protocol decoder
+
+import sigrokdecode as srd
+
+# Low-/full-speed symbols (used as states of our state machine, too).
+# Note: Low-speed J and K are inverted compared to the full-speed J and K!
+symbols_ls = {
+        # (<dp>, <dm>): <symbol/state>
+        (0, 0): 'SE0',
+        (1, 0): 'K',
+        (0, 1): 'J',
+        (1, 1): 'SE1',
+}
+symbols_fs = {
+        # (<dp>, <dm>): <symbol/state>
+        (0, 0): 'SE0',
+        (1, 0): 'J',
+        (0, 1): 'K',
+        (1, 1): 'SE1',
+}
+
+class Decoder(srd.Decoder):
+    api_version = 1
+    id = 'usb_signalling'
+    name = 'USB signalling'
+    longname = 'Universal Serial Bus (LS/FS) signalling'
+    desc = 'USB 1.x (low-speed and full-speed) signalling protocol.'
+    license = 'gplv2+'
+    inputs = ['logic']
+    outputs = ['usb_signalling']
+    probes = [
+        {'id': 'dp', 'name': 'D+', 'desc': 'USB D+ signal'},
+        {'id': 'dm', 'name': 'D-', 'desc': 'USB D- signal'},
+    ]
+    optional_probes = []
+    options = {
+        'signalling': ['Signalling', 'full-speed'],
+    }
+    annotations = [
+        ['Text', 'Human-readable text']
+    ]
+
+    def __init__(self):
+        self.sym = 'J' # The "idle" state is J.
+        self.samplenum = 0
+        self.scount = 0
+        self.packet = ''
+        self.syms = []
+
+    def start(self, metadata):
+        self.samplerate = metadata['samplerate']
+        self.out_proto = self.add(srd.OUTPUT_PROTO, 'usb_signalling')
+        self.out_ann = self.add(srd.OUTPUT_ANN, 'usb_signalling')
+
+    def report(self):
+        pass
+
+    def decode(self, ss, es, data):
+        for (self.samplenum, (dp, dm)) in data:
+
+            # Note: self.samplenum is the absolute sample number, whereas
+            # self.scount only counts the number of samples since the
+            # last change in the D+/D- lines.
+            self.scount += 1
+
+            if self.options['signalling'] == 'low-speed':
+                sym = symbols_ls[dp, dm]
+            elif self.options['signalling'] == 'full-speed':
+                sym = symbols_fs[dp, dm]
+
+            self.put(0, 0, self.out_ann, [0, [sym]])
+            self.put(0, 0, self.out_proto, ['SYM', sym])
+
+            # Wait for a symbol change (i.e., change in D+/D- lines).
+            if sym == self.sym:
+                continue
+
+            ## # Debug code:
+            ## self.syms.append(sym + ' ')
+            ## if len(self.syms) == 16:
+            ##     self.put(0, 0, self.out_ann, [0, [''.join(self.syms)]])
+            ##     self.syms = []
+            # continue
+
+            # How many bits since the last transition?
+            if self.packet != '' or self.sym != 'J':
+                if self.options['signalling'] == 'low-speed':
+                    bitrate = 1500000 # 1.5Mb/s (+/- 1.5%)
+                elif self.options['signalling'] == 'full-speed':
+                    bitrate = 12000000 # 12Mb/s (+/- 0.25%)
+                bitcount = int((self.scount - 1) * bitrate / self.samplerate)
+            else:
+                bitcount = 0
+
+            if self.sym == 'SE0':
+                if bitcount == 1:
+                    # End-Of-Packet (EOP)
+                    # self.put(0, 0, self.out_ann,
+                    #          [0, [packet_decode(self.packet), self.packet]])
+                    if self.packet != '': # FIXME?
+                        self.put(0, 0, self.out_ann, [0, ['PACKET: %s' % self.packet]])
+                        self.put(0, 0, self.out_proto, ['PACKET', self.packet])
+                else:
+                    # Longer than EOP, assume reset.
+                    self.put(0, 0, self.out_ann, [0, ['RESET']])
+                    self.put(0, 0, self.out_proto, ['RESET', None])
+                # self.put(0, 0, self.out_ann, [0, [self.packet]])
+                self.scount = 0
+                self.sym = sym
+                self.packet = ''
+                continue
+
+            # Add bits to the packet string.
+            self.packet += '1' * bitcount
+
+            # Handle bit stuffing.
+            if bitcount < 6 and sym != 'SE0':
+                self.packet += '0'
+            elif bitcount > 6:
+                self.put(0, 0, self.out_ann, [0, ['BIT STUFF ERROR']])
+                self.put(0, 0, self.out_proto, ['BIT STUFF ERROR', None])
+
+            self.scount = 0
+            self.sym = sym
+