From b6975c680c337bce650eb785d3dad96c282726b6 Mon Sep 17 00:00:00 2001
From: Gerhard Sittig <gerhard.sittig@gmx.net>
Date: Wed, 12 Aug 2020 18:47:37 +0200
Subject: sdq: simplify decode routine, no state machine required

Move the initial synchronization to the input data out of the main loop,
and handle the BREAK symbol when it was seen. Turns out that no state
machine is required to decode the SDQ protocol.

[ best viewed as a whitespace ignoring diff ]
---
 decoders/sdq/pd.py | 42 +++++++++++++++++-------------------------
 1 file changed, 17 insertions(+), 25 deletions(-)

(limited to 'decoders/sdq')

diff --git a/decoders/sdq/pd.py b/decoders/sdq/pd.py
index d8df89f..c65faa8 100644
--- a/decoders/sdq/pd.py
+++ b/decoders/sdq/pd.py
@@ -64,7 +64,6 @@ class Decoder(srd.Decoder):
 
     def reset(self):
         self.samplerate = None
-        self.state = 'INIT'
         self.startsample = 0
         self.bits = []
         self.bytepos = 0
@@ -98,30 +97,23 @@ class Decoder(srd.Decoder):
         self.bit_width = float(self.samplerate) / float(self.options['bitrate'])
         self.half_bit_width = self.bit_width / 2.0
         # BREAK if the line is low for longer than this.
-        self.break_threshold = self.bit_width * 1.2
+        break_threshold = self.bit_width * 1.2
 
+        # Wait until the line is high before inspecting input data.
+        sdq, = self.wait({0: 'h'})
         while True:
-            if self.state == 'INIT':
-                sdq, = self.wait({0: 'h'}) # Wait until the line is high before starting
-                self.state = 'DATA'
-
-            elif self.state == 'DATA':
-                sdq, = self.wait({0: 'f'}) # Falling edge
-
-                self.startsample = self.samplenum
-                if self.bytepos == 0:
-                    self.bytepos = self.samplenum
-
-                sdq, = self.wait({0: 'r'}) # Rising edge
-
-                delta = self.samplenum - self.startsample
-                if delta > self.break_threshold:
-                    self.state = 'BREAK'
-                elif delta > self.half_bit_width:
-                    self.handle_bit(0)
-                else:
-                    self.handle_bit(1)
-
-            elif self.state == 'BREAK':
+            # Get the length of a low pulse (falling to rising edge).
+            sdq, = self.wait({0: 'f'})
+            self.startsample = self.samplenum
+            if self.bytepos == 0:
+                self.bytepos = self.samplenum
+            sdq, = self.wait({0: 'r'})
+
+            # Check for 0 or 1 data bits, or the BREAK symbol.
+            delta = self.samplenum - self.startsample
+            if delta > break_threshold:
                 self.handle_break()
-                self.state = 'DATA'
+            elif delta > self.half_bit_width:
+                self.handle_bit(0)
+            else:
+                self.handle_bit(1)
-- 
cgit v1.2.3-70-g09d2