Figure 26-15. Event Output Generation
Beat Event Output
Data Transfer
Event Output
Data Transfer
Event Output
Block Transfer
BEAT
Block Event Output
Block Transfer
Block Transfer
Block Transfer
BEAT
BEAT
BEAT
BEAT
BEAT
BEAT
BEAT
26.6.3.6. Aborting Transfers
Transfers on any channel can be aborted gracefully by software by disabling the corresponding DMA
channel. It is also possible to abort all ongoing or pending transfers by disabling the DMAC.
When a DMA channel disable request or DMAC disable request is detected:
•
Ongoing transfers of the active channel will be disabled when the ongoing beat transfer is
completed and the write-back memory section is updated. This prevents transfer corruption before
the channel is disabled.
•
All other enabled channels will be disabled in the next clock cycle.
The corresponding Channel Enable bit in the Channel Control A register is cleared
(
.ENABLE=0) when the channel is disabled.
The corresponding DMAC Enable bit in the Control register is cleared (
.DMAENABLE=0) when the
entire DMAC module is disabled.
26.6.3.7. CRC Operation
A cyclic redundancy check (CRC) is an error detection technique used to find errors in data. It is
commonly used to determine whether the data during a transmission, or data present in data and
program memories has been corrupted or not. A CRC takes a data stream or a block of data as input and
generates a 16- or 32-bit output that can be appended to the data and used as a checksum.
When the data is received, the device or application repeats the calculation: If the new CRC result does
not match the one calculated earlier, the block contains a data error. The application will then detect this
and may take a corrective action, such as requesting the data to be sent again or simply not using the
incorrect data.
The CRC engine in DMAC supports two commonly used CRC polynomials: CRC-16 (CRC-CCITT) and
CRC-32 (IEEE 802.3). Typically, applying CRC-n (CRC-16 or CRC-32) to a data block of arbitrary length
will detect any single alteration that is ≤n bits in length, and will detect the fraction 1-2-n of all longer error
bursts.
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
451