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Table 12-4 describes an individual control-structure entry in the control table. Each entry is aligned on a
16-byte boundary. The entry contains four long words: the source end pointer, the destination end pointer,
the control word, and an unused entry. The inclusive end pointers point to the ending address of the
transfer. If the source or destination is nonincrementing (as for a peripheral register), then the pointer
should point to the transfer address.
Table 12-4. Channel Control Structure
Offset Description
0x000 Source end pointer
0x004 Destination end pointer
0x008 Control word
0x00C Unused entry
The control word contains the following fields:
• Source and destination data sizes
• Source and destination address increment size
• Number of transfers before bus arbitration
• Total number of items to transfer
• Useburst flag
• Transfer mode
The control parameters for a channel can be set using the driver library function void
uDMAChannelControlSet(); function. The μDMA controller updates the transfer size and transfer mode
fields as the transfer is performed. At the end of a transfer, the transfer size indicates 0, and the transfer
mode indicates stopped. Because the control word is modified by the μDMA controller, it must be
reconfigured before each new transfer. The source and destination end pointers are not modified, so they
can be left unchanged if the source or destination addresses remain the same.
Before starting a transfer, a μDMA channel must be enabled by setting the appropriate bit in the
[UDMA_SETCHANNELEN] register. A channel can be disabled by setting the channel bit in the
[UDMA_CLEARCHANNELEN] register. At the end of a complete μDMA transfer, the controller
automatically disables the channel.
12.3.6 Transfer Modes
The μDMA controller supports several transfer modes. Two of the modes support simple, one-time
transfers. Several complex modes support a continuous flow of data.
12.3.6.1 Stop Mode
While stop mode is not actually a transfer mode, stop is a valid value for the mode field of the control
word. When the mode field has the stop value, the μDMA controller does not perform any transfers and
disables the channel if enabled. The μDMA controller updates the control word to set the mode to stop at
the end of a transfer. This mode can be useful in scatter-gather.
12.3.6.2 Basic Mode
In basic mode, the μDMA controller performs transfers as long as there are more items to transfer, and a
transfer request is present. This mode is used with peripherals that assert a μDMA request signal
whenever the peripheral is ready for a data transfer. Basic mode should not be used in any situation
where the request is momentary, even though the entire transfer should be completed.
The μDMA controller sets the mode for that channel to stop when all of the items have been transferred
using basic mode.
1041
SWCU117A–February 2015–Revised March 2015 Micro Direct Memory Access (µDMA)
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