PXS20RM Datasheet, PDF (292/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Cyclic Redundancy Checker (CRC) Unit
Context = CRC_CNTX_NUM
Context = 1
START
CRC configuration
(polynomial, swap, inversion)
setting the CRC_CFG register
CRC seed initialization
(CRC_CSTAT register)
Data is written in the
CRC_INP register (byte/hword/word)
by CPU or DMA
No
All the
data has been passed
to the CRC unit
?
Yes
CRC signature available in the
CRC_OUTP register
Figure 14-8. CRC computation flow
14.7 Use cases and limitations
The number of contexts is dependent on the application. The overall number of contexts for the CRC
peripheral depends on the number of the peripherals that require concurrently the intervention of the CRC
module. 2 main use cases shall be considered:
— calculation of the CRC of the configuration registers during the process safety time
— calculation of the CRC on the incoming/outcoming frames for the communication protocols
(not protected with CRC by definition of the protocol itself) used as a safety-relevant
peripheral.
The signature of the configuration registers is computed in a correct way only if these registers do not
contain any status bit. Assuming that the DMA engine has N channels (greater or equal to the number of
contexts) configurable for the following type of data transfer: mem2mem, periph2mem, mem2periph, the
following sequence, as given in Figure 14-9, shall be applied to manage the transmission data flow:
14-8
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor