diff --git a/scripts/gdb.py b/scripts/gdb.py
index 286627c..6c6e02d 100644
--- a/scripts/gdb.py
+++ b/scripts/gdb.py
@@ -3,7 +3,7 @@
 # gdb.py: Python module for low level GDB protocol implementation
 # Copyright (C) 2009  Black Sphere Technologies
 # Written by Gareth McMullin <gareth@blacksphere.co.nz>
-# 
+#
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation, either version 3 of the License, or
@@ -24,24 +24,18 @@ import struct
 import time
 
 def hexify(s):
-	"""Convert a binary string into hex representation"""
-	ret = ''
-	for c in s:
-		ret += "%02X" % ord(c)
-	return ret
+	"""Convert a bytes object into hex bytes representation"""
+	return s.hex().encode()
 
 def unhexify(s):
-	"""Convert a hex string into binary representation"""
-	ret = ''
-	for i in range(0, len(s), 2):
-		ret += chr(int(s[i:i+2], 16))
-	return ret
+	"""Convert a hex-encoded bytes into bytes object"""
+	return bytes.fromhex(s.decode())
 
 class FakeSocket:
 	"""Emulate socket functions send and recv on a file object"""
 	def __init__(self, file):
 		self.file = file
-	
+
 	def send(self, data):
 		self.file.write(data)
 
@@ -52,148 +46,186 @@ class Target:
 	def __init__(self, sock):
 		if "send" in dir(sock):
 			self.sock = sock
-		else:	
+		else:
 			self.sock = FakeSocket(sock)
 
+		self.PacketSize=0x100 # default
+
 	def getpacket(self):
 		"""Return the first correctly received packet from GDB target"""
 		while True:
-			while self.sock.recv(1) != '$': pass
+			while self.sock.recv(1) != b'$':
+				pass
+
 			csum = 0
-			packet = ''
+			packet = [] # list-of-small-int
 
 			while True:
-				c = self.sock.recv(1)
-				if c == '#': break
+				c, = self.sock.recv(1)
+				if c == ord('#'):
+					break
 
-				if c == '$':
-					packet = ''
+				if c == ord('$'):
+					packet = []
 					csum = 0
 					continue
 
-				if c == '}':
-					c = self.sock.recv(1)
-					csum += ord(c) + ord('}')
-					packet += chr(ord(c) ^ 0x20)
-					continue	
+				if c == ord('}'):
+					c, = self.sock.recv(1)
+					csum += c + ord('}')
+					packet.append(c ^ 0x20)
+					continue
 
-				packet += c
-				csum += ord(c)
+				packet.append(c)
+				csum += c
 
-			if (csum & 0xFF) == int(self.sock.recv(2),16): break
+			if (csum & 0xFF) == int(self.sock.recv(2),16):
+				break
 
-			self.sock.send('-')
-		
-		self.sock.send('+')
-		return packet
+			self.sock.send(b'-')
 
+		self.sock.send(b'+')
+		return bytes(packet)
 
 	def putpacket(self, packet):
-		"""Send packet to GDB target and wait for acknowledge"""
+		"""Send packet to GDB target and wait for acknowledge
+		packet is bytes or string"""
+
+		if type(packet) == str:
+			packet = packet.encode()
+
 		while True:
-			self.sock.send('$')
-			csum = 0
+			out = []
+
 			for c in packet:
-				if (c == '$') or (c == '#') or (c == '}'):
-					self.sock.send('}')
-					self.sock.send(chr(ord(c) ^ 0x20))
-					csum += (ord(c) ^ 0x20) + ord('}')
+				if (c in b'$#}'):
+					out.append(ord('}'))
+					out.append(c ^ 0x20)
 				else:
-					self.sock.send(c)
-					csum += ord(c)
-			self.sock.send('#')
-			self.sock.send("%02X" % (csum & 0xFF))
-			if self.sock.recv(1) == '+': break
+					out.append(c)
+
+			csum = sum(out)
+			outb = b'$'+bytes(out)+b'#%02X' % (csum & 0xff)
+
+			self.sock.send(outb)
+			if self.sock.recv(1) == b'+':
+				break
 
 	def monitor(self, cmd):
 		"""Send gdb "monitor" command to target"""
+		if type(cmd) == str:
+			cmd = cmd.encode()
+
 		ret = []
-		self.putpacket("qRcmd," + hexify(cmd))
+		self.putpacket(b"qRcmd," + hexify(cmd))
 
 		while True:
 			s = self.getpacket()
-			if s == '': return None
-			if s == 'OK': return ret
-			if s.startswith('O'): ret.append(unhexify(s[1:]))
+
+			if s == b'':
+				return None
+			if s == b'OK':
+				return ret
+			if s.startswith(b'O'):
+				ret.append(unhexify(s[1:]))
 			else:
-				raise Exception('Invalid GDB stub response')
+				raise Exception('Invalid GDB stub response %r'%s.decode())
 
 	def attach(self, pid):
 		"""Attach to target process (gdb "attach" command)"""
-		self.putpacket("vAttach;%08X" % pid)
+		self.putpacket(b"vAttach;%08X" % pid)
 		reply = self.getpacket()
-		if (len(reply) == 0) or (reply[0] == 'E'): 
+		if (reply == b'') or (reply[:1] == b'E'):
 			raise Exception('Failed to attach to remote pid %d' % pid)
 
 	def detach(self):
 		"""Detach from target process (gdb "detach" command)"""
-		self.putpacket("D")
-		if self.getpacket() != 'OK': 
+		self.putpacket(b"D")
+		if self.getpacket() != b'OK':
 			raise Exception("Failed to detach from remote process")
 
 	def reset(self):
 		"""Reset the target system"""
-		self.putpacket("r")
+		self.putpacket(b"r")
 
 	def read_mem(self, addr, length):
 		"""Read length bytes from target at address addr"""
-		self.putpacket("m%08X,%08X" % (addr, length))
-		reply = self.getpacket()
-		if (len(reply) == 0) or (reply[0] == 'E'): 
-			raise Exception('Error reading memory at 0x%08X' % addr)
-		try:
-			data = unhexify(reply)
-		except Excpetion:
-			raise Exception('Invalid response to memory read packet: %r' % reply)
-		return data
-		
+		ret = b''
+		while length:
+			# print "Read"
+			packlen = min(length,self.PacketSize//2)
+			self.putpacket(b"m%08X,%08X" % (addr, packlen))
+			reply = self.getpacket()
+			if (reply == b'') or (reply[:1] == b'E'):
+				raise Exception('Error reading memory at 0x%08X' % addr)
+			try:
+				data = unhexify(reply)
+			except Exception:
+				raise Exception('Invalid response to memory read packet: %r' % reply)
+			ret += data
+			length -= packlen
+			addr += packlen
+
+		return ret
+
 	def write_mem(self, addr, data):
 		"""Write data to target at address addr"""
-		self.putpacket("X%08X,%08X:%s" % (addr, len(data), data))
-		if self.getpacket() != 'OK': 
-			raise Exception('Error writing to memory at 0x%08X' % addr)
+		data = bytes(data)
+
+		while data:
+			d = data[:self.PacketSize-44]
+			data = data[len(d):]
+			#print("Writing %d bytes at 0x%X" % (len(d), addr))
+			pack = b"X%08X,%08X:%s" % (addr, len(d), d)
+			self.putpacket(pack)
+
+			if self.getpacket() != b'OK':
+				raise Exception('Error writing to memory at 0x%08X' % addr)
+			addr += len(d)
 
 	def read_regs(self):
 		"""Read target core registers"""
-		self.putpacket("g")
+		self.putpacket(b"g")
 		reply = self.getpacket()
-		if (len(reply) == 0) or (reply[0] == 'E'): 
+		if (reply == b'') or (reply[:1] == b'E'):
 			raise Exception('Error reading memory at 0x%08X' % addr)
 		try:
 			data = unhexify(reply)
-		except Excpetion:
+		except Exception:
 			raise Exception('Invalid response to memory read packet: %r' % reply)
-		return struct.unpack("=20L", data)
+		ret = array.array('I',data)
+		return ret
 
 	def write_regs(self, *regs):
 		"""Write target core registers"""
 		data = struct.pack("=%dL" % len(regs), *regs)
-		self.putpacket("G" + hexify(data))
-		if self.getpacket() != 'OK': 
+		self.putpacket(b"G" + hexify(data))
+		if self.getpacket() != b'OK':
 			raise Exception('Error writing to target core registers')
 
 	def memmap_read(self):
 		"""Read the XML memory map from target"""
 		offset = 0
-		ret = ''
+		ret = b''
 		while True:
-			self.putpacket("qXfer:memory-map:read::%08X,%08X" % (offset, 512))
+			self.putpacket(b"qXfer:memory-map:read::%08X,%08X" % (offset, 512))
 			reply = self.getpacket()
-			if (reply[0] == 'm') or (reply[0] == 'l'):
+			if (reply[0] in b'ml'):
 				offset += len(reply) - 1
 				ret += reply[1:]
 			else:
-				raise Exception("Invalid GDB stub response")
+				raise Exception('Invalid GDB stub response %r'%reply)
+
+			if reply[:1] == b'l':
+				return ret
 
-			if reply[0] == 'l': return ret
-			
 	def resume(self):
 		"""Resume target execution"""
-		self.putpacket("c")
+		self.putpacket(b'c')
 
 	def interrupt(self):
 		"""Interrupt target execution"""
-		self.sock.send("\x03")
+		self.sock.send(b'\x03')
 
 	def run_stub(self, stub, address, *args):
 		"""Execute a binary stub at address, passing args in core registers."""
@@ -205,11 +237,19 @@ class Target:
 		regs[15] = address
 		self.write_regs(*regs)
 		self.resume()
-		reply = self.getpacket()
+		reply = None
 		while not reply:
 			reply = self.getpacket()
-		if not reply.startswith("T05"):
-			raise Exception("Invalid stop response: %r" % reply)
+		if not reply.startswith(b"T05"):
+			message = "Invalid stop response: %r" % reply
+			try:
+				message += {'T02':' (SIGINT)',
+							'T05':' (SIGTRAP)',
+							'T0B':' (SIGSEGV)',
+							'T1D':' (SIGLOST)'}[reply]
+			except KeyError:
+				pass
+			raise Exception(message)
 
 	class FlashMemory:
 		def __init__(self, target, offset, length, blocksize):
@@ -217,27 +257,30 @@ class Target:
 			self.offset = offset
 			self.length = length
 			self.blocksize = blocksize
-			self.blocks = list(None for i in range(length / blocksize))
+			self.blocks = list(None for i in range(length // blocksize))
 
 		def prog(self, offset, data):
-			assert ((offset >= self.offset) and 
+			assert type(data)==bytes
+
+			assert ((offset >= self.offset) and
 				(offset + len(data) <= self.offset + self.length))
 
 			while data:
-				index = (offset - self.offset) / self.blocksize
+				index = (offset - self.offset) // self.blocksize
 				bloffset = (offset - self.offset) % self.blocksize
 				bldata = data[:self.blocksize-bloffset]
 				data = data[len(bldata):]; offset += len(bldata)
 				if self.blocks[index] is None: # Initialize a clear block
-					self.blocks[index] = "".join(chr(0xff) for i in range(self.blocksize))
-				self.blocks[index] = (self.blocks[index][:bloffset] + bldata + 
+					self.blocks[index] = bytes(0xff for i in range(self.blocksize))
+				self.blocks[index] = (self.blocks[index][:bloffset] + bldata +
 						self.blocks[index][bloffset+len(bldata):])
 
 		def commit(self, progress_cb=None):
 			totalblocks = 0
 			for b in self.blocks:
-				if b is not None: totalblocks += 1
-				
+				if b is not None:
+					totalblocks += 1
+
 			block = 0
 			for i in range(len(self.blocks)):
 				block += 1
@@ -247,35 +290,37 @@ class Target:
 				# Erase the block
 				data = self.blocks[i]
 				addr = self.offset + self.blocksize * i
-				if data is None: continue
+				if data is None:
+					continue
 				#print "Erasing flash at 0x%X" % (self.offset + self.blocksize*i)
-				self.target.putpacket("vFlashErase:%08X,%08X" % 
+				self.target.putpacket(b"vFlashErase:%08X,%08X" %
 					(self.offset + self.blocksize*i, self.blocksize))
-				if self.target.getpacket() != 'OK': 
+				if self.target.getpacket() != b'OK':
 					raise Exception("Failed to erase flash")
 
 				while data:
 					d = data[0:980]
 					data = data[len(d):]
 					#print "Writing %d bytes at 0x%X" % (len(d), addr)
-					self.target.putpacket("vFlashWrite:%08X:%s" % (addr, d))
+					self.target.putpacket(b"vFlashWrite:%08X:%s" % (addr, d))
 					addr += len(d)
-					if self.target.getpacket() != 'OK': 
+					if self.target.getpacket() != b'OK':
 						raise Exception("Failed to write flash")
-					
-				self.target.putpacket("vFlashDone")
-				if self.target.getpacket() != 'OK': 
+
+				self.target.putpacket(b"vFlashDone")
+				if self.target.getpacket() != b'OK':
 					raise Exception("Failed to commit")
-			
-			self.blocks = list(None for i in range(self.length / self.blocksize))
-			
+
+			self.blocks = list(None for i in range(self.length // self.blocksize))
+
 
 	def flash_probe(self):
 		self.mem = []
 		xmldom = parseString(self.memmap_read())
-		
+
 		for memrange in xmldom.getElementsByTagName("memory"):
-			if memrange.getAttribute("type") != "flash": continue
+			if memrange.getAttribute("type") != "flash":
+				continue
 			offset = eval(memrange.getAttribute("start"))
 			length = eval(memrange.getAttribute("length"))
 			for property in memrange.getElementsByTagName("property"):
@@ -297,5 +342,3 @@ class Target:
 	def flash_commit(self, progress_cb=None):
 		for m in self.mem:
 			m.commit(progress_cb)
-
-
diff --git a/scripts/hexprog.py b/scripts/hexprog.py
index ccfb43c..43f9693 100755
--- a/scripts/hexprog.py
+++ b/scripts/hexprog.py
@@ -3,7 +3,7 @@
 # hexprog.py: Python application to flash a target with an Intel hex file
 # Copyright (C) 2011  Black Sphere Technologies
 # Written by Gareth McMullin <gareth@blacksphere.co.nz>
-# 
+#
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation, either version 3 of the License, or
@@ -31,15 +31,16 @@ def flash_write_hex(target, hexfile, progress_cb=None):
 	f = open(hexfile)
 	addrhi = 0
 	for line in f:
-		if line[0] != ':': raise Exception("Error in hex file")
+		if line[0] != ':':
+			raise Exception("Error in hex file")
 		reclen = int(line[1:3], 16)
 		addrlo = int(line[3:7], 16)
 		rectype = int(line[7:9], 16);
-		if sum(ord(x) for x in gdb.unhexify(line[1:11+reclen*2])) & 0xff != 0:
-			raise Exception("Checksum error in hex file") 
+		if sum(x for x in bytes.fromhex(line[1:11+reclen*2])) & 0xff != 0:
+			raise Exception("Checksum error in hex file")
 		if rectype == 0: # Data record
 			addr = (addrhi << 16) + addrlo
-			data = gdb.unhexify(line[9:9+reclen*2])
+			data = bytes.fromhex(line[9:9+reclen*2])
 			target.flash_write_prepare(addr, data)
 			pass
 		elif rectype == 4: # High address record
@@ -48,16 +49,16 @@ def flash_write_hex(target, hexfile, progress_cb=None):
 		elif rectype == 5: # Entry record
 			pass
 		elif rectype == 1: # End of file record
-			break 
+			break
 		else:
 			raise Exception("Invalid record in hex file")
 
 	try:
 		target.flash_commit(progress_cb)
 	except:
-		print "Flash write failed! Is device protected?\n"
+		print("Flash write failed! Is device protected?\n")
 		exit(-1)
-	
+
 
 if __name__ == "__main__":
 	from serial import Serial, SerialException
@@ -67,8 +68,8 @@ if __name__ == "__main__":
 	if platform == "linux2":
 		print ("\x1b\x5b\x48\x1b\x5b\x32\x4a") # clear terminal screen
 	print("Black Magic Probe -- Target Production Programming Tool -- version 1.0")
-	print "Copyright (C) 2011  Black Sphere Technologies"
-	print "License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>"
+	print("Copyright (C) 2011  Black Sphere Technologies")
+	print("License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>")
 	print("")
 
 	dev = "COM1" if platform == "win32" else "/dev/ttyACM0"
@@ -80,13 +81,20 @@ if __name__ == "__main__":
 	try:
 		opts, args = getopt(argv[1:], "sd:b:t:rR")
 		for opt in opts:
-			if opt[0] == "-s": scan = "swdp_scan"
-			elif opt[0] == "-b": baud = int(opt[1])
-			elif opt[0] == "-d": dev = opt[1]
-			elif opt[0] == "-t": targetno = int(opt[1])
-			elif opt[0] == "-r": unprot = True
-			elif opt[0] == "-R": prot = True
-			else: raise Exception()
+			if opt[0] == "-s":
+				scan = "swdp_scan"
+			elif opt[0] == "-b":
+				baud = int(opt[1])
+			elif opt[0] == "-d":
+				dev = opt[1]
+			elif opt[0] == "-t":
+				targetno = int(opt[1])
+			elif opt[0] == "-r":
+				unprot = True
+			elif opt[0] == "-R":
+				prot = True
+			else:
+				raise Exception()
 
 		hexfile = args[0]
 	except:
@@ -101,39 +109,44 @@ if __name__ == "__main__":
 		exit(-1)
 
 	try:
-		s = Serial(dev, baud, timeout=3)
-		s.setDTR(1)
-		while s.read(1024):
-			pass
+		s = Serial(dev) #, baud, timeout=0.1)
+		#s.setDTR(1)
+		#s.flushInput()
+
+		#while s.read(1024):
+	        #		pass
 
 		target = gdb.Target(s)
-		
-	except SerialException, e:
+
+	except SerialException as e:
 		print("FATAL: Failed to open serial device!\n%s\n" % e[0])
 		exit(-1)
 
 	try:
 		r = target.monitor("version")
-		for s in r: print s,
-	except SerialException, e:
+		for s in r:
+			print(s.decode(), end=' ')
+	except SerialException as e:
 		print("FATAL: Serial communication failure!\n%s\n" % e[0])
 		exit(-1)
-	except: pass
+	#except: pass
 
-	print "Target device scan:"
+	print("Target device scan:")
 	targetlist = None
 	r = target.monitor(scan)
-	for s in r: 
-		print s,
-	print
+	for s in r:
+		print(s.decode(), end=' ')
+	print()
 
 	r = target.monitor("targets")
-	for s in r: 
-		if s.startswith("No. Att Driver"): targetlist = []
+	for s in r:
+		if s.startswith(b"No. Att Driver"):
+			targetlist = []
 		try:
-			if type(targetlist) is list: 
+			if type(targetlist) is list:
 				targetlist.append(int(s[:2]))
-		except: pass
+		except:
+			pass
 
 	#if not targetlist:
 	#	print("FATAL: No usable targets found!\n")
@@ -161,7 +174,7 @@ if __name__ == "__main__":
 		print("FLASH memory -- Offset: 0x%X  BlockSize:0x%X\n" % (m.offset, m.blocksize))
 
 	def progress(percent):
-		print ("Progress: %d%%\r" % percent),
+		print("Progress: %d%%\r" % percent, end=' ')
 		stdout.flush()
 
 	print("Programming target")
@@ -179,4 +192,3 @@ if __name__ == "__main__":
 	target.detach()
 
 	print("\nAll operations complete!\n")
-