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
@@ -30,25 +25,42 @@ class SSS7Bus(object):
 		print "[SSS7Bus] %s" % msg
 
 
-	def _read_frame(self, clear_channel=False):
-		if clear_channel :
+	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()
+
 		self._serial.timeout = self._bit_time * CLEARCHANNEL
 		self._debug("Checking if bus is idle for %f seconds" % (self._bit_time * CLEARCHANNEL))
-		else:
+
+		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:
-			if clear_channel:
-				self._debug("Bus was idle")
-			else:	
 			self._debug("Timeout reading frame length")
-			return self.ERR_TIMEOUT_ON_LENGTH
+			return False
 
-		if clear_channel:
-			self._debug("Bus was not idle, trying to read frame")
+		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
@@ -59,7 +71,7 @@ class SSS7Bus(object):
 		# 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
+			return False
 
 		crc = data[-2:]
 		payload = data[:-2]
@@ -70,23 +82,14 @@ class SSS7Bus(object):
 
 		if real_crc != crc:
 			self._debug("Wrong crc for frame payload")
-			return self.ERR_CRC_ERRROR
+			return True
 
 		self._debug("Sucessfully read rest of frame")
 		self._buffer.insert(0,data)
 
-		return self.ERR_SUCCESS
+		return True
 
 
-	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
-
 
 	def _send_byte(self, byte):
 		self._serial.write(byte)
@@ -108,6 +111,9 @@ class SSS7Bus(object):
 
 
 	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()