srd: Performance improvements for various PDs.

Ignore/skip identical samples in most (low-level) PDs, as we're usually
(but not necessarily always) only interested in pin changes.

This yields a significant performance improvement for the PDs.

The mechanism was already used in the 'i2s', 'jtag', and 'lpc' PDs, but not
yet in all supported low-level decoders. The following PDs now also use
this mechanism: 'dcf77', 'i2c', 'spi', 'uart', and 'usb_signalling'.

Thanks Lars-Peter Clausen <lars@metafoo.de> for bringing this to our
attention.

5 files changed, 35 insertions, 5 deletions

diff --git a/decoders/dcf77/dcf77.py b/decoders/dcf77/dcf77.py
index 4da9bc4..c4132e9 100644
--- a/decoders/dcf77/dcf77.py
+++ b/decoders/dcf77/dcf77.py
@@ -50,6 +50,7 @@ class Decoder(srd.Decoder):
 
     def __init__(self, **kwargs):
         self.state = 'WAIT FOR RISING EDGE'
+        self.oldpins = None
         self.oldval = None
         self.oldpon = None
         self.samplenum = 0
@@ -197,7 +198,12 @@ class Decoder(srd.Decoder):
             raise Exception('Invalid DCF77 bit: %d' % c)
 
     def decode(self, ss, es, data):
-        for (self.samplenum, (val, pon)) in data:
+        for (self.samplenum, pins) in data:
+
+            # Ignore identical samples early on (for performance reasons).
+            if self.oldpins == pins:
+                continue
+            self.oldpins, (val, pon) = pins, pins
 
             # Always remember the old PON state.
             if self.oldpon != pon:
diff --git a/decoders/i2c/i2c.py b/decoders/i2c/i2c.py
index 0e79497..53321eb 100644
--- a/decoders/i2c/i2c.py
+++ b/decoders/i2c/i2c.py
@@ -88,6 +88,7 @@ class Decoder(srd.Decoder):
         self.state = 'FIND START'
         self.oldscl = None
         self.oldsda = None
+        self.oldpins = None
 
     def start(self, metadata):
         self.out_proto = self.add(srd.OUTPUT_PROTO, 'i2c')
@@ -198,7 +199,12 @@ class Decoder(srd.Decoder):
         super(Decoder, self).put(self.startsample, self.samplenum, output_id, data)
 
     def decode(self, ss, es, data):
-        for (self.samplenum, (scl, sda)) in data:
+        for (self.samplenum, pins) in data:
+
+            # Ignore identical samples early on (for performance reasons).
+            if self.oldpins == pins:
+                continue
+            self.oldpins, (scl, sda) = pins, pins
 
             # First sample: Save SCL/SDA value.
             if self.oldscl == None:
diff --git a/decoders/spi/spi.py b/decoders/spi/spi.py
index 2f10ef4..1085786 100644
--- a/decoders/spi/spi.py
+++ b/decoders/spi/spi.py
@@ -74,6 +74,7 @@ class Decoder(srd.Decoder):
         self.samplenum = -1
         self.cs_was_deasserted_during_data_word = 0
         self.oldcs = -1
+        self.oldpins = None
 
     def start(self, metadata):
         self.out_proto = self.add(srd.OUTPUT_PROTO, 'spi')
@@ -84,7 +85,12 @@ class Decoder(srd.Decoder):
 
     def decode(self, ss, es, data):
         # TODO: Either MISO or MOSI could be optional. CS# is optional.
-        for (self.samplenum, (miso, mosi, sck, cs)) in data:
+        for (self.samplenum, pins) in data:
+
+            # Ignore identical samples early on (for performance reasons).
+            if self.oldpins == pins:
+                continue
+            self.oldpins, (miso, mosi, sck, cs) = pins, pins
 
             if self.oldcs != cs:
                 # Send all CS# pin value changes.
diff --git a/decoders/uart/uart.py b/decoders/uart/uart.py
index bb4d9e6..92c105c 100644
--- a/decoders/uart/uart.py
+++ b/decoders/uart/uart.py
@@ -103,6 +103,7 @@ class Decoder(srd.Decoder):
         self.startsample = [-1, -1]
         self.state = ['WAIT FOR START BIT', 'WAIT FOR START BIT']
         self.oldbit = [None, None]
+        self.oldpins = None
 
     def start(self, metadata):
         self.samplerate = metadata['samplerate']
@@ -265,7 +266,12 @@ class Decoder(srd.Decoder):
 
     def decode(self, ss, es, data):
         # TODO: Either RX or TX could be omitted (optional probe).
-        for (self.samplenum, (rx, tx)) in data:
+        for (self.samplenum, pins) in data:
+
+            # Ignore identical samples early on (for performance reasons).
+            if self.oldpins == pins:
+                continue
+            self.oldpins, (rx, tx) = pins, pins
 
             # First sample: Save RX/TX value.
             if self.oldbit[RX] == None:
diff --git a/decoders/usb_signalling/usb_signalling.py b/decoders/usb_signalling/usb_signalling.py
index 512703d..3272cbf 100644
--- a/decoders/usb_signalling/usb_signalling.py
+++ b/decoders/usb_signalling/usb_signalling.py
@@ -67,6 +67,7 @@ class Decoder(srd.Decoder):
         self.scount = 0
         self.packet = ''
         self.syms = []
+        self.oldpins = None
 
     def start(self, metadata):
         self.samplerate = metadata['samplerate']
@@ -77,13 +78,18 @@ class Decoder(srd.Decoder):
         pass
 
     def decode(self, ss, es, data):
-        for (self.samplenum, (dp, dm)) in data:
+        for (self.samplenum, pins) 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
 
+            # Ignore identical samples early on (for performance reasons).
+            if self.oldpins == pins:
+                continue
+            self.oldpins, (dp, dm) = pins, pins
+
             if self.options['signalling'] == 'low-speed':
                 sym = symbols_ls[dp, dm]
             elif self.options['signalling'] == 'full-speed':