31.3.1 CRC initialization/reinitialization
To enable the CRC calculation, the user must program CRC_CTRL[WAS],
CRC_GPOLY,necessary parameters for transposition and CRC result inversion in the
applicable registers. Asserting CRC_CTRL[WAS] enables the programming of the seed
value into the CRC_DATA register.
After a completed CRC calculation, the module can be reinitialized for a new CRC
computation by reasserting CRC_CTRL[WAS] and programming a new, or previously
used, seed value. All other parameters must be set before programming the seed value
and subsequent data values.
31.3.2 CRC calculations
In 16-bit and 32-bit CRC modes, data values can be programmed 8 bits, 16 bits, or 32 bits
at a time, provided all bytes are contiguous. Noncontiguous bytes can lead to an incorrect
CRC computation.
31.3.2.1 16-bit CRC
To compute a 16-bit CRC:
1. Clear CRC_CTRL[TCRC] to enable 16-bit CRC mode.
2. Program the transpose and complement options in the CTRL register as required for
for details.
3. Write a 16-bit polynomial to the CRC_GPOLY[LOW] field. The
CRC_GPOLY[HIGH] field is not usable in 16-bit CRC mode.
4. Set CRC_CTRL[WAS] to program the seed value.
5. Write a 16-bit seed to CRC_DATA[LU:LL]. CRC_DATA[HU:HL] are not used.
6. Clear CRC_CTRL[WAS] to start writing data values.
7. Write data values into CRC_DATA[HU:HL:LU:LL]. A CRC is computed on every
data value write, and the intermediate CRC result is stored back into
CRC_DATA[LU:LL].
8. When all values have been written, read the final CRC result from
CRC_DATA[LU:LL].
Transpose and complement operations are performed on the fly while reading or writing
values. See
for details.
Functional description
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676
Freescale Semiconductor, Inc.
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