Atmel Evaluation Kit AT91SAM9G25-EK AT91SAM9G25-EK Data Sheet
Product codes
AT91SAM9G25-EK
481
SAM9G25 [DATASHEET]
11032C–ATARM–25-Jan-13
31.5
DMAC Software Requirements
z
There must not be any write operation to Channel registers in an active channel after the channel enable is made
HIGH. If any channel parameters must be reprogrammed, this can only be done after disabling the DMAC
channel.
HIGH. If any channel parameters must be reprogrammed, this can only be done after disabling the DMAC
channel.
z
When the destination peripheral has been defined as the flow controller, source single transfer requests are not
serviced until the destination peripheral has asserted its Last Transfer Flag.
serviced until the destination peripheral has asserted its Last Transfer Flag.
z
When the source peripheral has been defined as the flow controller, destination single transfer requests are not
serviced until the source peripheral has asserted its Last Transfer Flag.
serviced until the source peripheral has asserted its Last Transfer Flag.
z
When the destination peripheral has been defined as the flow controller, if the destination width is smaller than the
source width, then a data loss may occur, and the loss is equal to the Source Single Transfer size in bytes-
destination Single Transfer size in bytes.
source width, then a data loss may occur, and the loss is equal to the Source Single Transfer size in bytes-
destination Single Transfer size in bytes.
z
When a Memory to Peripheral transfer occurs, if the destination peripheral has been defined as the flow controller,
then a prefetch operation is performed. It means that data is extracted from the memory before any request from
the peripheral is generated.
then a prefetch operation is performed. It means that data is extracted from the memory before any request from
the peripheral is generated.
z
You must program the DMAC_SADDRx and DMAC_DADDRx channel registers with a byte, half-word and word
aligned address depending on the source width and destination width.
aligned address depending on the source width and destination width.
z
After the software disables a channel by writing into the channel disable register, it must re-enable the channel
only after it has polled a 0 in the corresponding channel enable status register. This is because the current AHB
Burst must terminate properly.
only after it has polled a 0 in the corresponding channel enable status register. This is because the current AHB
Burst must terminate properly.
z
If you program the BTSIZE field in the DMAC_CTRLA as zero, and the DMAC has been defined as the flow
controller, then the channel is automatically disabled.
controller, then the channel is automatically disabled.
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When hardware handshaking interface protocol is fully implemented, a peripheral is expected to deassert any sreq
or breq signals on receiving the ack signal irrespective of the request the ack was asserted in response to.
or breq signals on receiving the ack signal irrespective of the request the ack was asserted in response to.
z
Multiple Transfers involving the same peripheral must not be programmed and enabled on different channels,
unless this peripheral integrates several hardware handshaking interfaces.
unless this peripheral integrates several hardware handshaking interfaces.
z
When a Peripheral has been defined as the flow controller, the targeted DMAC Channel must be enabled before
the Peripheral. If you do not ensure this and the First DMAC request is also the last transfer, the DMAC Channel
might miss a Last Transfer Flag.
the Peripheral. If you do not ensure this and the First DMAC request is also the last transfer, the DMAC Channel
might miss a Last Transfer Flag.
z
When the AUTO Field is set to TRUE, then the BTSIZE Field is automatically reloaded from its previous value.
BTSIZE must be initialized to a non zero value if the first transfer is initiated with the AUTO field set to TRUE, even
if LLI mode is enabled, because the LLI fetch operation will not update this field.
BTSIZE must be initialized to a non zero value if the first transfer is initiated with the AUTO field set to TRUE, even
if LLI mode is enabled, because the LLI fetch operation will not update this field.