diff options
Diffstat (limited to 'glucometerutils/drivers')
-rw-r--r-- | glucometerutils/drivers/lifescan_common.py | 70 | ||||
-rw-r--r-- | glucometerutils/drivers/otultra2.py | 33 |
2 files changed, 86 insertions, 17 deletions
diff --git a/glucometerutils/drivers/lifescan_common.py b/glucometerutils/drivers/lifescan_common.py new file mode 100644 index 0000000..ac25d22 --- /dev/null +++ b/glucometerutils/drivers/lifescan_common.py @@ -0,0 +1,70 @@ +# -*- coding: utf-8 -*- +"""Common utility functions for LifeScan meters.""" + +__author__ = 'Diego Elio Pettenò' +__email__ = 'flameeyes@flameeyes.eu' +__copyright__ = 'Copyright © 2013, Diego Elio Pettenò' +__license__ = 'GPL v3 or later' + +import ctypes + +from glucometerutils import exceptions + + +class MissingChecksum(exceptions.InvalidResponse): + """The response misses the expected 4-digits checksum.""" + def __init__(self, response): + self.message = 'Response is missing checksum: %s' % response + + +class InvalidChecksum(exceptions.InvalidResponse): + def __init__(self, expected, gotten): + self.message = ( + 'Response checksum not matching: %04x expected, %04x gotten' % + (expected, gotten)) + + +class InvalidSerialNumber(exceptions.Error): + """The serial number is not as expected.""" + def __init__(self, serial_number): + self.message = 'Serial number %s is invalid.' % serial_number + + +def calculate_checksum(bytestring): + """Calculate the "CRC16 Sick" style checksum for LifeScan protocols. + + Args: + bytestring: the string of which the checksum has to be calculated. + + Returns: + A 16-bit integer that is the checksum for the input. + + Credits for this code go to Christian Navalici, who implemented it in his + library at https://github.com/cristianav/PyCRC/ . + """ + crcValue = 0x0000 + prev_c = 0x0000 + + for idx, c in enumerate(bytestring): + short_c = 0x00ff & c + + idx_previous = idx - 1 + short_p = ( 0x00ff & prev_c) << 8; + + if ( crcValue & 0x8000 ): + crcValue = ctypes.c_ushort(crcValue << 1).value ^ 0x8005 + else: + crcValue = ctypes.c_ushort(crcValue << 1).value + + crcValue &= 0xffff + crcValue ^= ( short_c | short_p ) + + prev_c = short_c + + # After processing, the one's complement of the CRC is calcluated and the + # two bytes of the CRC are swapped. + low_byte = (crcValue & 0xff00) >> 8 + high_byte = (crcValue & 0x00ff) << 8 + crcValue = low_byte | high_byte; + + return crcValue diff --git a/glucometerutils/drivers/otultra2.py b/glucometerutils/drivers/otultra2.py index f453dc9..ebfda8f 100644 --- a/glucometerutils/drivers/otultra2.py +++ b/glucometerutils/drivers/otultra2.py @@ -13,19 +13,7 @@ import serial from glucometerutils import common from glucometerutils import exceptions - - -class MissingChecksum(exceptions.InvalidResponse): - """The response misses the expected 4-digits checksum.""" - def __init__(self, response): - self.response = response - - def __str__(self): - return 'Response is missing the OT2 checksum: %s' % self.response - - -class InvalidSerialNumber(exceptions.Error): - """The serial number is not ending with Y as expected.""" +from glucometerutils.drivers import lifescan_common class Device(object): @@ -62,11 +50,22 @@ class Device(object): match = self._RESPONSE_MATCH.match(line) if not match: - raise MissingChecksum(line) + raise lifescan_common.MissingChecksum(line) + + response, checksum_string = match.groups() + + try: + checksum_given = int(checksum_string, 16) + checksum_calculated = lifescan_common.calculate_checksum( + bytes(response, 'ascii')) - response, checksum = match.groups() + if checksum_given != checksum_calculated: + raise lifescan_common.InvalidChecksum(checksum_given, + checksum_calculated) + except ValueError: + raise lifescan_common.InvalidChecksum(checksum_given, + None) - # TODO(flameeyes) check that the checksum is actually valid return response def _send_oneliner_command(self, cmd): @@ -122,7 +121,7 @@ class Device(object): # 'Y' at the far right of the serial number is the indication of a OneTouch # Ultra2 device, as per specs. if serial_number[-1] != 'Y': - raise InvalidSerialNumber('Serial number %s is invalid.' % serial_number) + raise lifescan_common.InvalidSerialNumber(serial_number) return serial_number |