srd: srd_usb.py: Cosmetics, white-space fixes.

diff --git a/decoders/srd_usb.py b/decoders/srd_usb.py
index 36fc9605712ba4b747a999f24455134e48f4b75e..128b337e50b83ee8c724ce5e3c9daa4ae0b0eeb5 100644 (file)
--- a/decoders/srd_usb.py
+++ b/decoders/srd_usb.py
@@ -18,21 +18,27 @@
 ## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 ##
 
+#
 # USB Full-speed protocol decoder
-
-# Full-speed usb singalling consists of two signal lines, both driven at 3.3V
-# logic levels.  The signals are DP and DM, and normally operate in 
-# differential mode.  
+#
+# Full-speed USB signalling consists of two signal lines, both driven at 3.3V
+# logic levels. The signals are DP (D+) and DM (D-), and normally operate in
+# differential mode.
 # The state where DP=1,DM=0 is J, the state DP=0,DM=1 is K.
-# A state SE0 is defined where DP=DM=0.  This common mode signal is used to
+# A state SE0 is defined where DP=DM=0. This common mode signal is used to
 # signal a reset or end of packet.
-
-# Data transmitted on the USB is encoded with NRZI.  A transision from J to K
-# or vice-versa indicates a logic 0, while no transision indicates a logic 1.
-# If 6 ones are transmitted consecutively, a zero is inserted to force a 
-# transition.  This is known as bit stuffing.  Data is transferred at a rate 
-# of 12Mbit/s.  The SE0 transmitted to signal an end-of-packet is two bit 
+#
+# Data transmitted on the USB is encoded with NRZI. A transition from J to K
+# or vice-versa indicates a logic 0, while no transition indicates a logic 1.
+# If 6 ones are transmitted consecutively, a zero is inserted to force a
+# transition. This is known as bit stuffing. Data is transferred at a rate
+# of 12Mbit/s. The SE0 transmitted to signal an end-of-packet is two bit
 # intervals long.
+#
+# Details:
+# https://en.wikipedia.org/wiki/USB
+# http://www.usb.org/developers/docs/
+#
 
 import sigrok
 
@@ -47,6 +53,7 @@ def sampleiter(data, unitsize):
     for i in range(0, len(data), unitsize):
         yield(Sample(data[i:i+unitsize]))
 
+# States
 SE0, J, K, SE1 = 0, 1, 2, 3
 syms = {
         (False, False): SE0,
@@ -62,13 +69,14 @@ def bitstr_to_num(bitstr):
     return int(''.join(l), 2)
 
 def packet_decode(packet):
-    pids = {'10000111':'OUT',  #Tokens
+    pids = {
+        '10000111':'OUT',      # Tokens
         '10010110':'IN',
         '10100101':'SOF',
         '10110100':'SETUP',
-        '11000011':'DATA0',    #Data
+        '11000011':'DATA0',    # Data
         '11010010':'DATA1',
-        '01001011':'ACK',      #Handshake
+        '01001011':'ACK',      # Handshake
         '01011010':'NAK',
         '01111000':'STALL',
         '01101001':'NYET',
@@ -77,7 +85,7 @@ def packet_decode(packet):
     sync = packet[:8]
     pid = packet[8:16]
     pid = pids.get(pid, pid)
-    #Remove CRC
+    # Remove CRC.
     if pid in ('OUT', 'IN', 'SOF', 'SETUP'):
         data = packet[16:-5]
         if pid == 'SOF':
@@ -99,7 +107,7 @@ def packet_decode(packet):
 
     if sync != "00000001":
         return "SYNC INVALID!"
-    
+
     return pid + ' ' + data
 
 class Decoder():
@@ -124,7 +132,7 @@ class Decoder():
         self.rate = metadata['samplerate']
         if self.rate < 48000000:
             raise Exception("Sample rate not sufficient for USB decoding")
-        # initialise decoder state
+        # Initialise decoder state.
         self.sym = J
         self.scount = 0
         self.packet = ''
@@ -134,19 +142,19 @@ class Decoder():
 
             self.scount += 1
 
-            sym = syms[sample.probe(self.probes['dp']), 
-                        sample.probe(self.probes['dm'])] 
+            sym = syms[sample.probe(self.probes['dp']),
+                       sample.probe(self.probes['dm'])]
             if sym == self.sym:
                 continue
 
             if self.scount == 1:
-                # We ignore single sample width pulses. 
-                # I sometimes get these with the OLS
+                # We ignore single sample width pulses.
+                # I sometimes get these with the OLS.
                 self.sym = sym
                 self.scount = 0
                 continue
 
-            # how many bits since the last transition?
+            # How many bits since the last transition?
             if self.packet or self.sym != J:
                 bitcount = (self.scount - 1) * 12000000 / self.rate
             else:
@@ -154,11 +162,11 @@ class Decoder():
 
             if self.sym == SE0:
                 if bitcount == 1:
-                    # End-Of-Packet
-                    sigrok.put({"type":"usb", "data":self.packet, 
+                    # End-Of-Packet (EOP)
+                    sigrok.put({"type":"usb", "data":self.packet,
                                 "display":packet_decode(self.packet)})
                 else:
-                     # Longer than EOP, assume reset
+                    # Longer than EOP, assume reset.
                     sigrok.put({"type":"usb", "display":"RESET"})
                 self.scount = 0
                 self.sym = sym
@@ -167,12 +175,12 @@ class Decoder():
 
             # Add bits to the packet string.
             self.packet += '1' * bitcount
-            # Handle bit stuffing
+            # Handle bit stuffing.
             if bitcount < 6 and sym != SE0:
                 self.packet += '0'
             elif bitcount > 6:
                 sigrok.put({"type":"usb", "display":"BIT STUFF ERROR"})
-            
+
             self.scount = 0
             self.sym = sym