Crc Registers - ST STM32L4x6 Reference Manual

RM0351
The CRC calculator can be initialized to a programmable value using the RESET control bit
in the CRC_CR register (the default value is 0xFFFFFFFF).
The initial CRC value can be programmed with the CRC_INIT register. The CRC_DR
register is automatically initialized upon CRC_INIT register write access.
The CRC_IDR register can be used to hold a temporary value related to CRC calculation. It
is not affected by the RESET bit in the CRC_CR register.
Polynomial programmability
The polynomial coefficients are fully programmable through the CRC_POL register, and the
polynomial size can be configured to be 7, 8, 16 or 32 bits by programming the
POLYSIZE[1:0] bits in the CRC_CR register. Even polynomials are not supported.
If the CRC data is less than 32-bit, its value can be read from the least significant bits of the
CRC_DR register.
To obtain a reliable CRC calculation, the change on-fly of the polynomial value or size can
not be performed during a CRC calculation. As a result, if a CRC calculation is ongoing, the
application must either reset it or perform a CRC_DR read before changing the polynomial.
The default polynomial value is the CRC-32 (Ethernet) polynomial: 0x4C11DB7.
13.4

CRC registers

13.4.1 Data register (CRC_DR)
Address offset: 0x00
Reset value: 0xFFFF FFFF
31 30 29
15 14 13
Bits 31:0 DR[31:0]: Data register bits
28 27 26 25
12 11 10 9
This register is used to write new data to the CRC calculator.
It holds the previous CRC calculation result when it is read.
If the data size is less than 32 bits, the least significant bits are used to write/read the
correct value.
DocID024597 Rev 3
Cyclic redundancy check calculation unit (CRC)
24 23 22 21
DR[31:16]
rw
8 7 6 5
DR[15:0]
rw
20 19 18 17
4 3 2 1
16
0
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