is used for simple transfer modes where transfers can be reconfigured and restarted after each
transfer is complete. In this case, the alternate control structures are not used and therefore only
the first half of the table must be allocated in memory; the second half of the control table is not
necessary, and that memory can be used for something else. If a more complex transfer mode is
used such as ping-pong or scatter-gather, then the alternate control structure is also used and
memory space should be allocated for the entire table.
Any unused memory in the control table may be used by the application. This includes the control
structures for any channels that are unused by the application as well as the unused control word
for each channel.
Table 8-3. Control Structure Memory Map
ChannelOffset
0, Primary0x0
1, Primary0x10
......
31, Primary0x1F0
0, Alternate0x200
1, Alternate0x210
......
31, Alternate0x3F0
Table 8-4 shows 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 end pointers point to the ending address of the
transfer and are inclusive. If the source or destination is non-incrementing (as for a peripheral
register), then the pointer should point to the transfer address.
Table 8-4. Channel Control Structure
DescriptionOffset
Source End Pointer0x000
Destination End Pointer0x004
Control Word0x008
Unused0x00C
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 word and each field are described in detail in “μDMA Channel Control
Structure” on page 371. The μDMA controller updates the transfer size and transfer mode fields as
353July 24, 2012
Texas Instruments-Production Data
Stellaris
®
LM3S6G65 Microcontroller
OBSOLETE: TI has discontinued production of this device.
