35
calculated CRC must be transmitted in order from
highest-order term to lowest-order term. UARTs
transmit characters in order from LSB to MSB. By
storing the CRC this way we hand it to the UART
in the order low-byte to high-byte; the UART
sends each low-bit to hight-bit; and the result is
transmission bit by bit from highest- to lowest-
order term without requiring any bit shuffling on
our part. Reception works similarly
The feedback terms table consists of 256, 32-bit
entries. Notes
The table can be generated at runtime if desired;
code to do so is shown later. It might not be
obvious, but the feedback terms simply represent
the results of eight shift/xor operations for all
combinations of data and CRC register values
The values must be right-shifted by eight bits by
the "updcrc logic; the shift must be unsigned (bring
in zeroes). On some hardware you could probably
optimize the shift in assembler by using byte-swap
instructions polynomial $edb88320
CRC32 code derived from work by Gary S. Brown.
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DRV-430_B5A-0959-01_EU_EN.indd 35 2017/12/21 12:13
