Add exception handling, remove possible infinite loops, add license and comments in spi module.

common/spi.py

 #!/usr/bin/python
 
+# Copyright CERN, 2011
+# Author: Matthieu Cattin (CERN)
+# Licence: GPL v2 or later.
+# Website: http://www.ohwr.org
+# Last modifications: 27/4/2012
+
+# Import standard modules
 import sys
-import rr
 import time
 
+# Import specific modules
+import rr
+
+# Class to access the wishbone to SPI master module from OpenCores
+# http://opencores.org/project,spi
+
+class SPIDeviceOperationError(Exception):
+    def __init__(self, msg):
+        self.msg = msg
+    def __str__(self):
+        return ("SPI Device produced the error: %s" %(msg))
+
 class COpenCoresSPI:
 
+        # OpenCores SPI registers description
 	R_RX = [0x00, 0x04, 0x08, 0x0C]
 	R_TX = [0x00, 0x04, 0x08, 0x0C]
 	R_CTRL = 0x10
@@ -23,10 +42,13 @@ class COpenCoresSPI:
 
         DIV_MASK = (0xFFFF)
 
-        SS_SEL = [0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40]
-
+        # Static variable
 	conf = 0x0
 
+        # Constant declaration
+        SS_SEL = [0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40]
+        WAIT_TIME_OUT = 2
+
 	def wr_reg(self, addr, val):
 		self.bus.iwrite(0, self.base_addr +  addr, 4, val)
 
@@ -37,12 +59,16 @@ class COpenCoresSPI:
 		self.bus = bus;
 		self.base_addr = base_addr;
 		self.wr_reg(self.R_DIV, (divider & self.DIV_MASK));
-		# default configuration
+		# Default configuration:
+                # ASS = Automatic Slave Select
+                # TXNEG = MOSI changes on SCLK falling edge
 		self.conf = self.CTRL_ASS | self.CTRL_TXNEG
 
 	def wait_busy(self):
-		while(self.rd_reg(self.R_CTRL) & self.CTRL_BSY):
-			pass
+                init_time=time.time()
+                while(self.rd_reg(self.R_CTRL) & self.CTRL_BSY):
+                        if (time.time()-init_time) > self.WAIT_TIME_OUT:
+                                raise I2CDeviceOperationError("Wait timeout")
 
 	def config(self, ass, rx_neg, tx_neg, lsb, ie):
 		self.conf = 0
@@ -58,26 +84,24 @@ class COpenCoresSPI:
 			self.conf |= self.CTRL_IE
 
 	# slave = slave number (0 to 7)
-	# data = byte data array to send, in case if read fill with dummy data of the right size
+	# data = byte data array to send,
+        #        in case of read, filled with dummy data of the right size
 	def transaction(self, slave, data):
 		txrx = [0x00000000, 0x00000000, 0x00000000, 0x00000000]
 		for i in range(0,len(data)):
 			txrx[i/4] += (data[i]<<((i%4)*8))
-			#print("tx[%d]=%.8X data[%d]=%.2X") %(i/4,txrx[i/4],i,data[i])
-
+			#print '[SPI] tx[%d]=%.8X data[%d]=%.2X' % (i/4,txrx[i/4],i,data[i])
 		for i in range(0, len(txrx)):
 			self.wr_reg(self.R_TX[i], txrx[i])
-
-		#print('data length: 0x%X')%len(data)
+		#print '[SPI] data length: 0x%X' % len(data)
 		self.wr_reg(self.R_SS, self.SS_SEL[slave])
 		self.wr_reg(self.R_CTRL, (self.LGH_MASK & (len(data)<<3)) | self.CTRL_GO | self.conf)
 		self.wait_busy()
-
 		for i in range(0, len(txrx)):
 			txrx[i] = self.rd_reg(self.R_RX[i])
-			#print("rx[%d]=%.8X") %(i,txrx[i])
-
+			#print '[SPI] rx[%d]=%.8X' % (i,txrx[i])
 		return txrx
 
+# Usage example
 #gennum = rr.Gennum();
 #spi = COpenCoresSPI(gennum, 0x80000, 500);