parallel: unbreak and improve "word" de-multiplexing

The previous implementation prepared but never fully enabled the
accumulation of several multi-bit items into words that span multiple
bus cycles (think: address or data de-multiplexing on memory busses).

Complete the accumulation, and fixup the end samplenumber for word
annotations. Fixup the endianess logic (the condition was inverted).
Rephrase calculation to be more Python idiomatic.

Default to word size zero, and only emit word annotations for non-zero
word size specs. This keeps the implementation backwards compatible and
still passes the test suite. Default behaviour is most appropriate for
interactive use in GUI environments, while automated processing will
find consistent behaviour across all setups (non-multiplexed busses, and
multiplexed busses with "words" that span one or multiple cycles).

1 files changed, 28 insertions, 19 deletions

diff --git a/decoders/parallel/pd.py b/decoders/parallel/pd.py
index 1c3435c..364332a 100644
--- a/decoders/parallel/pd.py
+++ b/decoders/parallel/pd.py
@@ -79,7 +79,7 @@ class Decoder(srd.Decoder):
     options = (
         {'id': 'clock_edge', 'desc': 'Clock edge to sample on',
             'default': 'rising', 'values': ('rising', 'falling')},
-        {'id': 'wordsize', 'desc': 'Data wordsize', 'default': 1},
+        {'id': 'wordsize', 'desc': 'Data wordsize', 'default': 0},
         {'id': 'endianness', 'desc': 'Data endianness',
             'default': 'little', 'values': ('little', 'big')},
     )
@@ -87,6 +87,10 @@ class Decoder(srd.Decoder):
         ('items', 'Items'),
         ('words', 'Words'),
     )
+    annotation_rows = (
+        ('items', 'Items', (0,)),
+        ('words', 'Words', (1,)),
+    )
 
     def __init__(self):
         self.reset()
@@ -95,6 +99,8 @@ class Decoder(srd.Decoder):
         self.items = []
         self.saved_item = None
         self.ss_item = self.es_item = None
+        self.saved_word = None
+        self.ss_word = self.es_word = None
         self.first = True
 
     def start(self):
@@ -114,11 +120,19 @@ class Decoder(srd.Decoder):
         self.put(self.ss_word, self.es_word, self.out_ann, data)
 
     def handle_bits(self, item, used_pins):
-        # Save the item, and its sample number if it's the first part of a word.
-        if not self.items:
-            self.ss_word = self.samplenum
-        self.items.append(item)
 
+        # If a word was previously accumulated, then emit its annotation
+        # now after its end samplenumber became available.
+        if self.saved_word is not None:
+            if self.options['wordsize'] > 0:
+                self.es_word = self.samplenum
+                self.putw([1, ['%X' % self.saved_word]])
+                self.putpw(['WORD', self.saved_word])
+            self.saved_word = None
+
+        # Defer annotations for individual items until the next sample
+        # is taken, and the previous sample's end samplenumber has
+        # become available.
         if self.first:
             # Save the start sample and item for later (no output yet).
             self.ss_item = self.samplenum
@@ -132,26 +146,21 @@ class Decoder(srd.Decoder):
             self.ss_item = self.samplenum
             self.saved_item = item
 
-        # Get as many items as the configured wordsize says.
+        # Get as many items as the configured wordsize specifies.
+        if not self.items:
+            self.ss_word = self.samplenum
+        self.items.append(item)
         ws = self.options['wordsize']
         if len(self.items) < ws:
             return
 
-        # Output annotations/python for a word (a collection of items).
-        # NOTE that this feature is currently not effective. The emission
-        # of Python annotations is commented out.
+        # Collect words and prepare annotation details, but defer emission
+        # until the end samplenumber becomes available.
         endian = self.options['endianness']
-        if endian == 'little':
+        if endian == 'big':
             self.items.reverse()
-        word = 0
-        for i in range(ws):
-            word |= self.items[i] << (i * used_pins)
-
-        self.es_word = self.samplenum
-        # self.putpw(['WORD', word])
-        # self.putw([1, ['%X' % word]])
-        self.ss_word = self.samplenum
-
+        word = sum([self.items[i] << (i * used_pins) for i in range(ws)])
+        self.saved_word = word
         self.items = []
 
     def decode(self):