Cleaned up control flow

software/python/sss7bus.py

@@ -12,11 +12,6 @@ CLEARCHANNEL = 48
 
 
 class SSS7Bus(object):
-	ERR_SUCCESS = 0
-	ERR_TIMEOUT_ON_LENGTH = -1
-	ERR_TIMEOUT_ON_PAYLOAD = -2
-	ERR_CRC_ERRROR = -3
-
 
 	def __init__(self, port, baudrate=9600):
 		self._bit_time = 1.0 / baudrate
@@ -25,74 +20,82 @@ class SSS7Bus(object):
 
 		self._buffer = []
 
-	
+
 	def _debug(self, msg):
 		print "[SSS7Bus] %s" % msg
 
 
-	def _read_frame(self, clear_channel=False):
-		if clear_channel :
-			self._serial.timeout = self._bit_time * CLEARCHANNEL
-			self._debug("Checking if bus is idle for %f seconds" % (self._bit_time * CLEARCHANNEL))
-		else:
-			self._debug("Trying to read a frame from the bus")
-			self._serial.timeout = timeout=self._bit_time * TIMEOUT
-		
-		length_byte = self._serial.read(1)
-		if len(length_byte) == 0:
-			if clear_channel:
-				self._debug("Bus was idle")
-			else:	
-				self._debug("Timeout reading frame length")
-			return self.ERR_TIMEOUT_ON_LENGTH
-
-		if clear_channel:
-			self._debug("Bus was not idle, trying to read frame")
-
-		length = ord(length_byte) - 1 # we read the size length byte already
-		
-		self._serial.timeout = timeout=self._bit_time * TIMEOUT
-	
-		self._debug("Trying to read remaing %d bytes of frame" % length)
-		data = self._serial.read(length)
-		
-		# if read returns less then length, no new byte has been received for timeout seconds
-		if len(data) != length:
-			self._debug("Timeout reading frame payload")
-			return self.ERR_TIMEOUT_ON_PAYLOAD
-
-		crc = data[-2:]
-		payload = data[:-2]
-		
-		crc16 = PredefinedCrc('crc16')
-		crc16.update(payload)
-		real_crc = crc16.digest()
-
-		if real_crc != crc:
-			self._debug("Wrong crc for frame payload")
-			return self.ERR_CRC_ERRROR
-
-		self._debug("Sucessfully read rest of frame")
-		self._buffer.insert(0,data)
-	
-		return self.ERR_SUCCESS
-
-
 	def _flush_input_buffer(self):
 		while self._serial.inWaiting() > 0:
 			self._debug("Flushing input buffer")
 			self._read_frame()
 
+
 	def _can_send(self):
 		self._flush_input_buffer()
-		return self._read_frame(True) == self.ERR_TIMEOUT_ON_LENGTH
 
-	
+		self._serial.timeout = self._bit_time * CLEARCHANNEL
+		self._debug("Checking if bus is idle for %f seconds" % (self._bit_time * CLEARCHANNEL))
+
+		length_byte = self._serial.read(1)
+		if len(length_byte) == 0:
+			self._debug("Bus seems idle")
+			return True
+
+		self._debug("Bus is not idle, reading frames")
+		self._read_frame_rest(length_byte)
+
+		return False
+
+
+	def _read_frame(self):
+		self._debug("Trying to read a frame from the bus")
+		self._serial.timeout = timeout=self._bit_time * TIMEOUT
+
+		length_byte = self._serial.read(1)
+		if len(length_byte) == 0:
+			self._debug("Timeout reading frame length")
+			return False
+
+		return self._read_frame_rest(length_byte)
+
+
+	def _read_frame_rest(self, length_byte):
+		length = ord(length_byte) - 1 # we read the size length byte already
+
+		self._serial.timeout = timeout=self._bit_time * TIMEOUT
+
+		self._debug("Trying to read remaing %d bytes of frame" % length)
+		data = self._serial.read(length)
+
+		# if read returns less then length, no new byte has been received for timeout seconds
+		if len(data) != length:
+			self._debug("Timeout reading frame payload")
+			return False
+
+		crc = data[-2:]
+		payload = data[:-2]
+
+		crc16 = PredefinedCrc('crc16')
+		crc16.update(payload)
+		real_crc = crc16.digest()
+
+		if real_crc != crc:
+			self._debug("Wrong crc for frame payload")
+			return True
+
+		self._debug("Sucessfully read rest of frame")
+		self._buffer.insert(0,data)
+
+		return True
+
+
+
 	def _send_byte(self, byte):
 		self._serial.write(byte)
 		return byte == self._serial.read(1)
 
-	
+
 	def _send_frame(self, frame):
 		while not self._can_send():
 			pass
@@ -102,12 +105,15 @@ class SSS7Bus(object):
 			if not result:
 				self._debug("Sending frame failed with collision")
 				return False
-		
+
 		self._debug("Successfully send frame")
 		return True
 
 
 	def send_message(self, msg, priority=5):
+		if len(msg) > 253:
+			raise ValueError("Message length can not exceed 253 byte")
+
 		crc16 = PredefinedCrc('crc16')
 		crc16.update(msg)
 		msg_crc = crc16.digest()