diff options
Diffstat (limited to 'glucometerutils/drivers/lifescan_common.py')
-rw-r--r-- | glucometerutils/drivers/lifescan_common.py | 70 |
1 files changed, 70 insertions, 0 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 |