94 lines
2.9 KiB
Python
94 lines
2.9 KiB
Python
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# Usage: AHT20 crc8 checker.
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# A total of 6 * 8 bits data need to check. G(x) = x8 + x5 + x4 + 1 -> 0x131(0x31), Initial value = 0xFF. No XOROUT.
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# Author: XU Zifeng.
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# Email: zifeng.xu@foxmail.com
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N_DATA = 6
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# 1 * 8 bits CRC
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N_CRC = 1
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# Initial value. Equal to bit negation the first data (status of AHT20)
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INIT = 0xFF
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# Useful value to help calculate
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LAST_8_bit = 0xFF
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# Devide number retrieve from CRC-8 MAXIM G(x) = x8 + x5 + x4 + 1
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CRC_DEVIDE_NUMBER = 0x131
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# Data and CRC taken from AHT20, use this for testing?
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TEST_DATA = [[28, 184, 245, 165, 156, 208, 163], [28, 185, 16, 149, 156, 83, 112], [
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28, 184, 249, 85, 156, 114, 213], [28, 185, 9, 53, 156, 54, 45], [28, 185, 70, 117, 156, 189, 33], [28, 185, 64, 165, 156, 61, 209]]
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def mod2_division_8bits(a, b, number_of_bytes, init_value):
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"calculate mod2 division in 8 bits. a mod b. init_value is for crc8 init value."
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head_of_a = 0x80
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# Processiong a
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a = a << 8
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# Preprocessing head_of_a
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for i in range(0, number_of_bytes):
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head_of_a = head_of_a << 8
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b = b << 8
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init_value = init_value << 8
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a = a ^ init_value
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while (head_of_a > 0x80):
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# Find a 1
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if (head_of_a & a):
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head_of_a = head_of_a >> 1
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b = b >> 1
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a = a ^ b
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else:
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head_of_a = head_of_a >> 1
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b = b >> 1
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# This will show calculate the remainder
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# print("a:{0}\thead of a:{1}\tb:{2}".format(
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# bin(a), bin(head_of_a), bin(b)))
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return a
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def AHT20_crc8_calculate(all_data_int):
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init_value = INIT
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# Preprocess all the data and CRCCode from AHT20
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data_from_AHT20 = 0x00
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# Preprocessing the first data (status)
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# print(bin(data_from_AHT20))
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for i_data in range(0, len(all_data_int)):
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data_from_AHT20 = (data_from_AHT20 << 8) | all_data_int[i_data]
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# print(bin(data_from_AHT20))
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mod_value = mod2_division_8bits(
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data_from_AHT20, CRC_DEVIDE_NUMBER, len(all_data_int), init_value)
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# print(mod_value)
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return mod_value
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def AHT20_crc8_check(all_data_int):
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"""
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The input data shoule be:
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Status Humidity0 Humidity1 Humidity2|Temperature0 Temperature1 Temperature2 CRCCode.
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In python's int64.
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"""
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mod_value = AHT20_crc8_calculate(all_data_int[:-1])
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if (mod_value == all_data_int[-1]):
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return True
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else:
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return False
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def CRC8_check(all_data_int, init_value=0x00):
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divider = 0x107
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DATA_FOR_CHECK = all_data_int[0]
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for data in all_data_int[1:-1]:
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DATA_FOR_CHECK = (DATA_FOR_CHECK << 8) | data
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remainder = mod2_division_8bits(
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DATA_FOR_CHECK, divider, len(all_data_int) - 1, init_value)
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if (remainder == all_data_int[-1]):
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return True
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else:
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return False
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if __name__ == "__main__":
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print(CRC8_check([0x66, 0x44, 0x33, 0x22, 0x24], 0))
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for data in TEST_DATA:
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print(AHT20_crc8_check(data))
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