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Fixed UID to be four bytes long #50

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Fixed UID to be four bytes long #50

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22 changes: 13 additions & 9 deletions pirc522/rfid.py
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,14 @@ def __init__(self, bus=0, device=0, speed=1000000, pin_rst=def_pin_rst,
GPIO.output(pin_ce, 1)
self.init()

@staticmethod
def __uid_checksum(uid):
"""Computes the checksum (XOR) of the UID"""
serial_number_check = 0
for i in range(4):
serial_number_check = serial_number_check ^ uid[i]
return serial_number_check

def init(self):
self.reset()
self.dev_write(0x2A, 0x8D)
Expand Down Expand Up @@ -225,24 +233,19 @@ def anticoll(self):
back_data = []
serial_number = []

serial_number_check = 0

self.dev_write(0x0D, 0x00)
serial_number.append(self.act_anticl)
serial_number.append(0x20)

(error, back_data, back_bits) = self.card_write(self.mode_transrec, serial_number)
if not error:
if len(back_data) == 5:
for i in range(4):
serial_number_check = serial_number_check ^ back_data[i]

if serial_number_check != back_data[4]:
if self.__uid_checksum(back_data) != back_data[4]:
error = True
else:
error = True

return (error, back_data)
return (error, back_data[:4])

def calculate_crc(self, data):
self.clear_bitmask(0x05, 0x04)
Expand Down Expand Up @@ -277,8 +280,9 @@ def select_tag(self, uid):
buf.append(self.act_select)
buf.append(0x70)

for i in range(5):
buf.append(uid[i])
assert len(uid) == 4
buf.extend(uid)
buf.append(self.__uid_checksum(uid))

crc = self.calculate_crc(buf)
buf.append(crc[0])
Expand Down