CRC Checksum Generation
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SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
CRC Module
15.3 CRC Checksum Generation
The CRC generator is first initialized by writing a 16-bit word (seed) to the CRC Initialization and Result
(CRCINIRES) register. Any data that should be included into the CRC calculation must be written to the
CRC Data Input (CRCDI or CRCDIRB) register in the same order that the original CRC signature was
calculated. The actual signature can be read from the CRCINIRES register to compare the computed
checksum with the expected checksum.
Signature generation describes a method of how the result of a signature operation can be calculated. The
calculated signature, which is computed by an external tool, is called checksum in the following text. The
checksum is stored in the product's memory and is used to check the correctness of the CRC operation
result.
15.3.1 CRC Implementation
To allow parallel processing of the CRC, the linear feedback shift register (LFSR) functionality is
implemented with an XOR tree. This implementation shows the identical behavior as the LFSR approach
after 8 bits of data are shifted in when the LSB is 'shifted' in first. The generation of a signature calculation
has to be started by writing a seed to the CRCINIRES register to initialize the register. Software or
hardware (for example, the DMA) can transfer data to the CRCDI or CRCDIRB register (for example, from
memory). The value in CRCDI or CRCDIRB is then included into the signature, and the result is available
in the signature result registers at the next read access (CRCINIRES and CRCRESR). The signature can
be generated using word or byte data.
If a word data is processed, the lower byte at the even address is used at the first clock (MCLK) cycle.
During the second clock cycle, the higher byte is processed. Thus, it takes two clock cycles to process
word data, while it takes only one clock (MCLK) cycle to process byte data.
Data bytes written to CRCDIRB in word mode or the data byte in byte mode are bit-wise reversed before
the CRC engine adds them to the signature. The bits among each byte are reversed. Data bytes written to
CRCDI in word mode or the data byte in byte mode are not bit reversed before use by the CRC engine.
If the checksum itself (with reversed bit order) is included into the CRC operation (as data written to
CRCDI or CRCDIRB), the result in the CRCINIRES and CRCRESR registers must be zero.