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XMEGA B [DATASHEET]
8291B–AVR–01/2013
24.3
Operation
The data source for the CRC module must be selected in software as either flash memory, the DMA channels, or the I/O
interface. The CRC module then takes data input from the selected source and generates a checksum based on these
data. The checksum is available in the CHECKSUM registers in the CRC module. When CRC-32 polynomial is used, the
final checksum read is bit reversed and complemented (see
).
For the I/O interface or DMA controller, which CRC polynomial is used is software selectable, but the default setting is
CRC-16. CRC-32 is automatically used if Flash Memory is selected as the source. The CRC module operates on bytes
only.
Figure 24-1.
CRC generator block diagram.
24.4
CRC on Flash memory
A CRC-32 calculation can be performed on the entire flash memory, on only the application section, on only the boot
section, or on a software selectable range of the flash memory. Other than selecting the flash as the source, all further
control and setup are done from the NVM controller. This means that the NVM controller configures the memory range to
perform the CRC on, and the CRC is started using NVM commands. Once completed, the result is available in the
checksum registers in the CRC module. For further details on setting up and performing CRC on flash memory, refer to
“Memory Programming” on page 377
24.5
CRC on DMA Data
CRC-16 or CRC-32 calculations can be performed on data passing through any DMA channel. Once a DMA channel is
selected as the source, the CRC module will continuously generate the CRC on the data passing through the DMA
channel. The checksum is available for readout once the DMA transaction is completed or aborted. A CRC can be
DATAIN
CTRL
Flash
Memory
DMA
Controller
CRC-16
CRC-32
CHECKSUM
bit-r
complement
16
8
8
32
Checksum read
crc32
Содержание XMEGA B
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